Hyperplasia in a Gland With Hormone Excess

Abstract

Five syndromes share predominantly hyperplastic glands with primary excess of hormone. 1) NEONATAL SEVERE PRIMARY HYPERPARATHYROIDISM, from homozygous mutated CASR, begins severely in utero. 2) CONGENITAL NON-AUTOIMMUNE THYROTOXICOSIS, from mutated TSHR, varies from severe with fetal onset to mild with adult onset. 3) FAMILIAL MALE-LIMITED PRECOCIOUS PUBERTY, from mutated LHR, expresses testosterone over-secretion in young boys. 4) HEREDITARY OVARIAN HYPERSTIMULATION SYNDROME, from mutated FSHR, expresses symptomatic vascular permeabilities during pregnancy. 5) FAMILIAL HYPERALDOSTERONISM TYPE IIIA, from mutated KCNJ5, presents in young children with hypertension and hypokalemia.

Grouping of these 5 syndromes highlights predominant hyperplasia as a stable tissue endpoint, and as their tissue stage for all the hormone excess. Comparisons were made among this and 2 other groups of syndromes, forming a continuum of tissue staging [A-B-C]. A) Predominant oversecretions express little or no hyperplasia. B) Predominant hyperplasias express little or no neoplasia. C) Predominant neoplasias express nodules, adenomas, or cancers. Hyperplasias may progress (5 of 5) to neoplastic stages while predominant oversecrertions rarely do (1 of 6; frequencies differ P<0.02). Hyperplasias do not show tumor multiplicity (0 of 5) unlike neoplasias that do (14 of 20; P<.02). Hyperplasias express mutation of a plasma membrane-bound sensor (5 of 5) while neoplasias rarely do (RET) (1 of 18; P<.0002).

In conclusion, the multiple distinguishing themes within the hyperplasias establish a robust pathophysiology. It has the shared and novel feature of mutant sensors in the plasma membrane, suggesting that these are a major contributor to hyperplasia.

INTRODUCTION

Hyperplasia was identified long ago in pathologic tissues, including the thyroid and parathyroid, and long before the secreted hormone of each tissue had become identified (Hirsch A 1885; De Crecchio, L 1865; Erdheim J 1907). Hyperplasia is frequently a secondary state, a response to extracellular stimuli, such as in a goiter caused by thyroid stimulating antibodies or by TSH.

Alternately, and whether accompanied by oversecretion, hyperplasia can be a primary state, originating from an intrinsic process of the same cells (Derwahl M, Studer H 2002; Arnold A 2011; Snow AL, Xiao W, et al 2012). Primary hyperplasia usually accompanies a pathologic over-secretion of a hormone from the same cells. For this, it can be divided into two broad formats. The first is subtle hyperplasia as a precursor or an accompaniment to predominating adenomas or cancers (Mete O, Asa SL 2013; Marx SJ 2013). The second format is predominating hyperplasia but with little or no progression to adenomas or cancer. This second format is the main subject here.

METHODS

The main foci for review were histologic staging in hormone-secretory glands, secretion processes in the glands, germline mutation, and molecular functions around the mutant protein. I analyzed reports and reviews about: (a) primary over-secretion of hormone(s), (b) descriptions of light microscopy for the over-secreting glands, (c) predominating hyperplasia in the hormone-secretory gland, and (d) origin of the syndrome from a known mutation.

The main criterion for hyperplasia of a tissue is an increase in the number of relatively normal-appearing cells (Kumar V, Abbas AK, 2010). Hyperplasia is distinct from hypertrophy; hypertyrophy is an increase in cell size, and it can accompany hyperplasia. Hyperplastic cells may be of uniform or of mixed types. When of mixed types, there is a variable decrease in the fraction with adipocytes and other stroma. The parenchymal pattern is diffuse throughout a hyperplastic tissue, in contrast to neoplasia which is focal or multifocal. Differential immunostaining for reticulin has been used only occasionally to distinguish hyperplasia from neoplasia, but mainly for hepatic or pituitary tissues (Hong H, Patonay B, et al 2011; Mete O, Asa SL 2013).

Exclusion criteria (Supplementary Table S-1) included insufficient information about gland histology, predominantly normal or near-normal tissue grade (Marx 2014), or higher grades of neoplasia (small nodules, large nodules, adenoma, or cancer). Some of the excluded syndromes were later grouped for comparisons to the reviewed group.

We used Fisher’s exact test to compare frequencies of features among syndrome groups.

RESULTS

Neonatal severe primary hyperparathyroidism

Clinical.

Neonatal severe primary hyperparathyroidism (NSHPT) is very rare (Thompson NW, Carpenter LC, et al 1978; Cooper L, Wertheimer J, et al 1986; Key L, Thorne M, et al 1990; Arnold A, Marx SJ 2013). It includes an under-mineralized skeleton, sub-periosteal resorption, bell-shaped thorax, and extremely high blood levels of calcium (20–30 mg/dl) and of PTH (500% or more of the upper normal limit). Biallelic inactivation of the CaS-R in bone cells may contribute to the severe skeletal features (Goltzman D, Hendy GN 2015). These severely ill neonates suffer respiratory distress, worsened by multiple rib fractures and hypotonia. They need complex support. After subtotal parathyroidectomy, hyperparathyroidism in severe form recurred rapidly, at 2 and 5 months for two cases (Thompson NW, Carpenter LC, et al 1978; Key L, Thorne M, et al 1990) (Supplement). The preferred treatment includes urgent total parathyroidectomy.

Parathyroids in NSHPT.

The severe skeletal expressions at birth in NSHPT indicate that harmful over-secretion of PTH had begun from the parathyroid glands of the fetus. In fact, the murine fetus with homozygous CASR knockout, has serum PTH about 20-fold the maternal level at day 18 of gestation (Simmonds CS, Karsenty G, et al 2010). Surgery for NSHPT at 2–12 weeks postpartum has shown parathyroid size 4–10 times normal (Supplementary Table S-2). The histologic pattern is diffuse chief cell hyperplasia, mainly large clear cells and some small chief cells. Parathyroid nodularity or cancer have not been reported, and monoclonality has not been analyzed. However, double adenoma was identified in a variant, i.e. one case with germline biallelic inactivation of the CASR and much milder onset in adulthood (Hannan FM, Nesbit MA, et al 2010).

Molecules and genes.

The normal CASR encodes the extracellular calcium sensing receptor (CaS-R). It is expressed mainly on the parathyroid cell surface, but also on the renal tubular cell, the thyroidal C-cell, and elsewhere. It is central in sensing levels of extracellular calcium and in regulating PTH secretion (Brown EM 2013). A role in proliferation of the parathyroid has been supported indirectly by CaS-R deficiencies in the large parathyroids of primary or secondary hyperparathyroidism and also by calcimimetic drug actions against hyperparathyroidism (Kifor O, Moore FD, et al 1996; Farnebo P, Enberg U, et al 1997; Miller G, Davis J, et al 2011).

Cases of NSHPT have biallelic inactivation of the CASR (Marx SJ, Fraser D, et al 1985; Pollak MR, Brown EM, et al 1993; Hannan FM, Nesbit MA, et al 2012). The same mutation in heterozygous form expresses as familial hypocalciuric hypercalcemia (FHH) (Arnold A, Marx SJ 2013). GNA11 and AP2S1, two other genes less frequently mutated in FHH heterozygotes (Nesbit MA, Hannan F, et al 2013a; Nesbit MA, Hannan FM, et al 2013b), have not yet been implicated in NSHPT. 30% of the CASR mutations causing NSHPT predict truncation of the CaS-R vs 3% from the CASR mutations causing FHH; most of the missense CASR mutations are clustered in a limited extracellular domain (cleft of its “Venus fly-trap” domain) (Hannan FM, Nesbit MA, et al 2012). In vitro, most shift the suppression curve between extracellular Ca++ and PTH secretion towards higher Ca++ values (Pearce SHS, Bai M, et al 1996).

Sporadic tumor from somatic mutation of CASR.

The parathyroids from common primary hyperparathyroidism show decreased sensitivity to extracellular calcium (Brown EM, Gardner DG, et al 1979). Both primary and secondary tumors of the parathyroids show lowered concentrations of CaS-R protein (Kifor O, Moore FD, et al 1996; Farnebo P, Enberg U, et al 1997); however, somatic mutation of the CASR in the parathyroids has not been found in either of these common states (Hosokawa Y, Pollak MR, et al 1995; Arnold A, Brown ME, et al J Clin Invest 1995; Cetani F, Pinchera A, et al 1999). Rare cases of FHH present with a clinical diagnosis of parathyroid adenoma (Burski K, Torjussen B, et al 2002; Yamauchi M, Sugimoto T, et al 2002; Brachet C, Boros E, et al 2009; Yabuta T, Miyauchi A, et al 2009); these have not been evaluated for a second hit at the CASR or at another gene.

Variants related to NSHPT.

Rare homozygous CASR mutations are expressed as a milder variant, presenting as hypocalciuric hypercalcemia in adulthood (Leitman SA, Tenenbaum-Rakover Y, et al 2009; Hannan FM, Nesbit MA, et al 2010).

A different variant of intermediate severity (serum calcium 11–15 mg/dl and PTH 300% or more of upper normal) may occur in a neonate with heterozygous mutated CASR, but born to a mother without the mutation. In these cases, secondary hyperparathyroidism starting in the fetus in utero may worsen temporarily the otherwise mild expressions in the heterozygous neonate (Marx SJ, Attie MF, et al 1982; Bai M, Pearce SHS, et al 1997).

Congenital non-autoimmune thyrotoxicosis

Clinical.

Congenital non-autoimmune thyrotoxicosis (CNT) is rare and is generally caused by heterozygous activating mutation of the TSH receptor (TSH-R) (Kopp P, van Sande J, et al 1995; Vassart G 2010; Hebrant A, van Staveren WCG, et al 2011). It must be distinguished from the more frequent neonatal Graves disease, caused by antibodies that activate the TSH-R. Severe expressions can sometimes be recognized at birth; cases with earliest expressions show hyperthyroidism (50%), prematurity (70%), low birth weight (85%), mental retardation (60%), advanced bone age (50%), and cranial synostosis (50%) (Vassart G 2010; Hebrant A, van Staveren WCG, et al 2011). Most severely affected neonates present sporadically with a new mutation (Kopp P, van Sande J, et al; 1995; Polak M, et al 1996; Gozu HI, Lublinghoff J, et al 2010; Vassart G 2010; Hebrant A, van Staveren WCG, et al 2011). Alternately and rarely, an affected neonate was the offspring of an affected father or mother, who had been adequately managed as a severely affected child (Supornsilchai V, Sahakitrungruang T, et al 2009). In some families with TSH-R mutation, all carriers show onset of thyrotoxicosis after age 10 years (Arturi F, Chiefari E, et al 2002; Nishihara E, Chen C-R, et al 2010). Recurrence of thyrotoxicosis with CNT is likely after subtotal treatments, including after withdrawal of anti-thyroid drugs (Hebrant A, van Staveren WCG, et al 2011; Paschke R, Niedziela M, et al 2012). The usual treatment is uninterrupted antithyroid drugs and/or thyroid ablation, total or near-total.

Thyroid gland in CNT.

The severe expressions in some cases with CNT indicate that there had been over-secretion of thyroid hormones by the fetus. Thyroid histology near parturition in CNT has not been reported, but over 50% show goiter at birth. At all older ages, there is diffuse thyroid follicular hyperplasia, with or without goiter. Average thyroid size may be increased 3–5 fold or more. There are clusters of small or large follicles, similar to toxic thyroid adenoma. At later stages, small or large nodules may occur (Hebrant A, van Staveren WCG, et al 2011; Gozu HI, Lublinghoff J, et al 2010). The frequency of thyroid cancer is not increased.

Molecules and genes.

The normal TSH-R, LH receptor (LH-R or LH/CG-R), and FSH receptor (FSH-R) are closely related. Similarly the gonadotropin hormones, TSH, LH, FSH, and CG, are closely related (Themmen APN 2005; Kleinau G, Neumann S, et al 2013; Jiang X, Dias JA, et al 2014). All recently reported hereditary cases of CNT have had a heterozygous activating TSHR mutation. Most of the mutations are modeled along the transmembrane loops of the TSH-R, with roughly similar distribution of severe and less severe mutations (Gozu HI, Lublinghoff J, et al 2010). Mutation sequences from the severest cases can also be identical to mutations in sporadic adenoma. In contrast, less severe cases are from other private germline mutations. The mutated, activated TSH-R causes in vitro a 2–7 fold higher basal cyclic AMP than controls (Gozu HI, Lublinghoff J, et al 2010). Responsivity to TSH in vitro is conserved, and apparent affinity for TSH is sometimes increased (Vassart G 2010). Activating mutation of the TSH-R also stimulates thyrocyte proliferation in vitro (Ludgate M, Gire V, et al 1999).

Sporadic tumors from somatic mutation of the TSHR.

50% of autonomous solitary thyroid adenomas have a somatic activating mutation of the TSHR (Vassart G 2010; Hebrant A, van Staveren WCG, et al 2011). TSHR activating mutations have rarely been identified as an initiator in sporadic follicular thyroid cancer (Spambalg D, Sharifi N, et al 1996).

Variant from TSHR mutation, expressed as gestational thyrotoxicosis.

Thyrotoxicosis beginning in pregnancy is usually caused by Graves disease or by CG activation of the normal TSH-Rs. In one family, a mother and daughter showed severe hyperthyroidism, occurring and recurring during six pregnancies of one or the other (Rodien P, Bremont C, et al 1998). TSH was low and CG was normal for stage of gestation. A small diffuse goiter was recognized during a recurrence. The same germline change (mutation) of the TSHR was found in both cases. In vitro, this increased markedly the TSH-R sensitivity to CG but not to TSH.

Familial male-limited precocious puberty

Clinical.

Familial male-limited precocious puberty (FMPP) or testotoxicosis is initially recognized as male iso-sexual precocious puberty. Female carriers have no disease phenotype. Expression usually begins between ages 1–3 years (Beas FO, Zurbrugg RP, et al 1962; Egli CA, SM, Grumbach MM, et al 1985); the occasional expression as increased genital size at birth indicates onset in the fetus of such a case (Beas FO, Zurbrugg RP, et al 1962; Rosenthal SM, Grumbach MM, et al 1983; Müller J, Gondos B, et al 1998). Testosterone levels in blood are increased and gonadotrophins are low. Drugs against androgen synthesis or action have accomplished partial success (Reiter EO, Mauras N, et al 2010; Fuqua JS T 2013).

Testis in FMPP.

In FMPP, there is bilateral enlargement of the genitals, including modest enlargement of the testes. The testis in FMPP shows hyperplasia of Leydig cells, precocious spermatogenesis, and rarely bilateral nodularity of Leydig cells, (Gondos B, Egli CA, et al 1985; Leschek EW, Chan W-Y, et al 2001; McGee SR, Narayan P. 2013).

Molecules and genes.

FMPP is usually attributable to germline activating mutation of the LH-R (Themmen APN 2005; Shenker A, Laue L, et al 1993). The germline and somatic activating LHR mutations 2011). In vitro, these mutations elevate basal cyclic AMP but decrease the maximal cyclic AMP response to CG (Leschek EW, Chan W-Y, et al 2001).

Sporadic tumor arising from somatic mutation of LHR.

Most sporadic Leydig cell tumors have a somatically mutated LHR. Most adenomas show LHR D578H. The abnormalities of cyclic AMP regulation in vitro are more severe (higher basal cyclic AMP and absent response to CG) from D578H than from germline mutations; furthermore, D578H has not been identified in the germline and thus may be lethal in the very early embryo (Boot AM, Lumbroso S, et al 2011).

Hereditary ovarian hyperstimulation syndrome

Clinical.

When severe, hereditary ovarian hyperstimulation syndrome (OHSS) can be a life-threatening complex of ovarian enlargement and diffuse vascular permeability (ascites, pleural effusion, hemo-concentration, thromboembolism). It reflects over-secretion from the ovarian corpus luteum of pregnancy for several factors, including estrogens, progestins, and cytokines (Fiedler K, Ezcurra D 2012). Most frequently, ovarian hyperstimulation syndrome occurs sporadically during administration of exogenous FSH or CG for in vitro fertilization; in this setting, FSH may have been given to compensate for a subtle deficiency of FSH. Rarely, during an unassisted pregnancy, OHSS occurs and can recur spontaneously in several pregnancies of the same woman, and it may arise in several women within a family (Vasseur C, Rodien P, et al 2003; Smits G, Olatunbosun O, et al 2003). OHSS remits after delivery. The management is general support until and after delivery.

Corpus luteum of pregnancy in OHSS.

In OHSS, the ovaries are larger than in normal pregnancy and multicystic; there are layers of hyperplasia of luteinized granulosa and theca cells (Stocco C, Telleria C, et al 2007; Meduri G, Bachelot A, et al 2008). The ovaries in OHSS return to normal size by 8 weeks after delivery (Smits G, Olatunbosun O, et al 2003).

Molecules and genes.

Most gain of function changes or mutations in the FSHR were in the transmembrane domains (Desai SS, Roy BS, et al 2013). In vitro these mutations do not alter basal cyclic AMP; however, they broaden or shift the increase of cyclic AMP to lower concentrations of CG and sometimes also to TSH.

Sporadic tumor arising from somatic mutation of FSHR.

Mutation of the FSHR has not been reported in sporadic gonadal tumors.

Variant with autonomous spermatogenesis in males.

Normal spermatogenesis despite undetectable FSH was reported in two unrelated males with germline activating mutation of the FSHR. Undetectable FSH in one was attributed to prior surgery for a pituitary tumor and was from unknown cause in the other (Gromoll J, Simoni M, et al 1996: Casas-González P, Scaglia HE, et al 2012). It is likely that FSH release was also inhibited by oversecretion of inhibin or other factors from the testis.

Familial hyperaldosteronism type IIIA

Clinical.

Familial hyperaldosteronism type IIIA (HAIIIA) (Footnote 1) is rare (Geller DS, Zhang J, et al 2008; Choi M, Scholl UI, et al 2011; Scholl UI, Nelson-Williams C, et al 2012; Scholl UI, Lifton RP 2013; Mulatero P, Monticone S, et al 2013). It is generally recognized at ages 1–7 years as hypokalemia, mild hypertension, and very high aldosterone levels. Treatment with blockade of the aldosterone receptors is unsuccessful; and subtotal adrenalectomy generally is followed by persistence or rapid recurrence. Total adrenalectomy is the preferred treatment.

Adrenal cortex in HAIIIA.

Normal secretion of aldosterone is stimulated by increases of extracellular K+ or by angiotensin II (Spat A, Hunyady L 2004; Bollag WP 2014; Romero CA, Orias M, et al 2015). The renin/angiotensin system is not otherwise covered here. In HAIIIA, the adrenal cortex shows massive hyperplasia that is occasionally micronodular and thst is mainly in the fasciculata, with atrophy in the glomerulosa ((Geller DS, Zhang J, et al 2008; Scholl UI, Lifton RP 2013). This distribution contrasts to the glomerulosa predominant location of normal secretion of aldosterone The cause of this distribution of steroid synthesis is not known, but it might relate to stronger KCNJ5 expression in the normal glomerulosa.

The adrenal enlargement is age-dependent (Scholl UI, Nelson-Williams C, et al 2012); from extrapolation, the hyperplasia might have begun only after birth.

Molecules and genes.

There are more than 80 mammalian genes in the family of potassium channel subunits. Some of the inwardly rectifying K+ channels (thus “Kir”) also function as K+ sensors (Spat A, Hunyady L 2004; Hibino H, Inanobe A, et al 2010). They allow a small outflow or “leak” of K+ from cytoplasm to the exterior, while they restrict external Na+ from traversing inward through its K+-selective pore. Recent studies in aldosteronomas first identified Kir3.4 (encoded by the KCNJ5 gene) as a major K+ channel subunit and a major regulator of aldosterone secretion (Choi M, Scholl UI, et al 2011). Kir3.4 is normally expressed in adrenal glomerulosa, nerve, and muscle (Kokunai Y, Nakata T, et al 2014).

Patients with HAIIIA have germline heterozygous missense mutation of KCNJ5. Most of its inactivating mutations in HAIII or in sporadic aldosteronoma model to within the pore of the K+ selectivity filter (Scholl UI, Nelson-Williams C, et al 2012; Murthy M, Xu S, et al 2014). Most mutations are G151R, T158A, or I157S. A milder familial phenotype has also been recognized recently from 3 different mutations of KCNJ5 that model outside of the K+ selectivity pore (Murthy M, Xu S, et al 2014). All the evaluated germline and somatic KCNJ5 mutations in HAIIIA, HAIIIB, or sporadic aldosteronoma cause a loss of function of Kir3.4 (Scholl UI, Lifton RP 2013). They cause loss of K+ selectivity, and thus increased influx of Na+ through Kir3.4. Some mutations also cause decreased surface expression of Kir3.4 (Cheng CJ, Sung CC, et al 2014).

Another loss of function mutation, restricted to one sequence, KCNJ5 G151E, causes HAIIIB, a different syndrome of hereditary primary hyperaldosteronism, with normal adrenocortical size and normal morphology (Scholl UI, Nelson-Williams C, et al 2012; Mulatero P, Tauber P, et al 2012; Marx SJ 2014) (Footnote 1).

Sporadic tumor arising from somatic mutation of KCNJ5.

KCNJ5 is mutated in 40% of sporadic aldosteronomas, moreso in aldosteronoma of women than men, and not in adrenocortical cancers (Scholl UI, Nelson-Williams C, et al 2012; Scholl UI, Lifton RP 2013; Mulatero P, Monticone S, et al 2013). KCNJ5 mutation also has been found selectively in the dominant nodule of sporadic multinodular adrenal glands (Dekkers T, Meer T, et al 2014). Though considered as loss of function mutations, the missense mutations of KCNJ5 have been heterozygous in aldosteronomas, i.e. haploinsufficient or without inactivation of the normal allele (Choi M, Scholl UI, et al 2011).

DISCUSSION:

Broad Themes Among Many Syndromes

Broad theme: Wide range of severity of a clinical feature within a syndrome

I reviewed major features within 5 selected syndromes (Table 1, Table 2). Some of the themes were shared and important but were also shared among many other syndromes. For example, overall clinical severity can cover a broad spectrum. The main determinant of severity of a syndrome is often the sequence of the germline mutation (Vassart G 2010; Hebrant A, van Staveren WCG, et al 2011; Christensen SE, Nissen PH, et al 2011; Murthy M, Xu S, et al 2014).

Table 1.

Some clinical features of hereditary syndromes of primary hyperplasia with hormone excess (See also Table 2).

Syndrome	Normal serum stimulus of mutant sensor	Hormone over-secreted	Typical early age of onset of hormone excess	Selected comments about expressions
NSHPT#	Low Ca++	PTH	In fetus	Severe defects at birth reflect onset by fetal over-secretion of PTH
CNT	TSH	T4, T3	In fetus	Severe defects at birth reflect onset by fetal over-secretion of iodo-thyronines
FMPP	LH	Testosterone	1-3 yr	Not expressed in female carriers of the mutation
OHSS	CG	Estrogens, progestins, cytokines	Pregnant female	CG from the normal placenta stimulates the mutant FSH receptors in the corpus luteum of pregnancy
HAIIIA	K+	Aldosterone	1 yr	Hyperplasia is in the adrenal fasciculata with atrophy in the adrenal glomerulosa

^#Abbreviations: Congenital neonatal thyrotoxicosis CNT; Neonatal severe primary hyperparathyroidism NSHPT; hyperaldosteronism type III HAIII; Familial male-limited precocious puberty FMPP; Ovarian hyperstimulation syndrome OHSS

Table 2.

Features of mutated tissue in hereditary syndromes of primary hyperplasia with hormone excess (See also Table 1).

Syndrome nodules	Genes and germline mutations @	Mutated sensor moleule	Tissue over-functioning	Predominat hyperplasia	Progress to or adenomas – – – – – – – – –
Sporadic					Germline
					origin	origin
NSHPT#	CASR=	CaS-R	Parathyroid	Yes	Rare	No
CNT	TSHR+	TSH-R	Thyroid follicle	Yes	Yes	Yes
FMPP	LHR+	LH-R	Leydig cell of testis	Yes	Rare	Yes
OHSS	FSHR+	FSH-R	Corpus luteum of pregnancy	Yes	Yes	No
HAIIIA	KCNJ5−	Kir3.4	Adrenal cortex	Yes	Yes	Yes

^#Abbreviations: Congenital neonatal thyrotoxicosis CNT; Neonatal severe primary hyperparathyroidism NSHPT; hyperaldosteronism type III HAIII; Familial male-limited precocious puberty FMPP; Ovarian hyperstimulation syndrome OHSS. CaS-R extracellular calcium sensing receptor; TSH-R TSH receptor; LH-R LH receptor; FSH-R FSH receptor; Kir3.4 inward rectifying potassium channel subunit 3.4;.

^@Mutation types are: − heterozygous loss of function (inactivation); = homozygous loss of function (inactivation); + heterozygous gain of function (activation).

A less frequent determinant of severity is change of gene dosage in the germline. In particular, a double dose of the mutated CASR causes severe expressions in the form of NSHPT, whereas a single dose of the same CASR mutation is expressed far more mildly as FHH (Pollak MR, Brown EM, et al 1993; Pollak MR, Chou Y-H W, et al 1994; Arnold A, Marx SJ 2013).

Broad theme: Wide range of ages at onset

Earlier age of onset and greater severity of expression often go together; the earliest onsets may even be lethal to the embryo. Embryonic lethality was speculated for certain mutations of the TSHR or of the LHR, mainly because those mutations had been found in sporadic tumors but not in a germline (Hebrant A, van Staveren WCG, et al 2011; Boot AM, Lumbroso S, et al 2011).

For some severely affected neonates with either CNT or NSHPT, the syndrome must have started in the fetus with gland hyperplasia and toxicity from a hormone over-secreted. Furthermore, some less severe forms of expression are also likely to have begun in utero with or without recognition of their prenatal onset in utero (Beas FO, Zurbrugg RP, et al 1962; Rosenthal SM, Grumbach MM, et al 1983; Müller J, Gondos B, et al 1998). Still milder forms of expression show later onsets that are usually consistent within a family - during infancy, childhood, or adulthood. Lastly, some of the mildest carrier states have remained occult even during genetic evaluation in an adult (Nishihara E, Chen C-R, et al 2010). The latest onsets probably reflect the mildest forms of expression and the slowest gland enlargement over years.

An exception can be the requirement for late onset. In particular, either of the two syndromes, of OHSS or gestational thyrotoxicosis, can be expressed only in a female and only selectively during the unique window of her pregnancy.

Broad theme: Wide time interval until post-operative recurrence

Post-operative recurrence generally reflects dysfunctioin in residual tissues after surgery (Marx SJ 2013). Each cell in the remnant secretory tissue carries the germline defect; furthermore, remnant cells might have already become over-active (such as predominantly mono-clonal) before the time of surgery.

The average time interval until recurrence after subtotal surgery is another feature that might help to characterize a syndrome. The interval until recurrence of hyperparathyroidism (severe) was 2 and 5 months in two cases of NSHPT (Thompson NW, Carpenter LC, et al 1978; Key L, Thorne M, et al 1990;) (Supplement). This differs from the much longer interval of 12 years until recurrence (mild) for hyperparathyroidism in MEN1 (Rizzoli R, Green J III, et al 1985). And this also differs importantly from the even shorter average recurrence interval of 5 days (for mild hyperparathyroidism) after subtotal parathyroidectomy in FHH; the latter reflects immediate post-operative over-secretion independent of recurrent gland growth (Law WM jr Heath H III 1985; Marx SJ 2014).

Duration of the interval until postoperative recurrence was not documented in detail for the other 4 syndromes herein. It seems likely that hyperplasia from severe mutations expressed early (as in NSHPT or CNT) would recur more rapidly, and that mild mutations would have slower growth of the gland and would recur more slowly or, for some cases, not at all during prolonged followup (Nishihara E, Chen C-R, et al 2010).

Broad theme: Wide relevance of the genes to neoplasia

Any primary or secondary hyperplasia is typically regarded as a polyclonal process (Derwahl M, Studer H 2002; Arnold A 2011; Mete O, Asa SL 2013). However, mono-clonal components may also be inherent parts within hyperplasia. (Arnold A, Brown ME, et al 1995; Diaz-Cano SJ, de Miguel M, et al 2001; Korpershoek E, Petri BJ, et al 2014; Hartmann LC, Degnim AC, et al 2015).

Mutations can also contribute to sporadic cancers in diverse tissues, with any being a likely driver mutation in 0.1–5.0 % of most or all common cancer types (Bamford S, Dawson E, et al 2004; O’Hayre M, JV, Kufeva I, et al 2013). For example, the large intestine from over 1000 cancers tested per gene shows mutations in the following frequencies: CASR 4.5%, TSHR 5.7%, LHR 3.6%, FSHR 2.6%, KCNJ5 1.9% (Bamford S, Dawson E, et al 2004).

Distinguishing Themes Within 5 Hyperplasia Syndromes

Distinguishing theme: Predominant hyperplasia as an endpoint of expression in a gland

Hyperplasia results from an increased rate of cell birth and/or decreased rate of cell death in the gland. The quantitative disturbances of either process have not been analyzed herein, excepting indirectly as contributions by neoplasia-related processes (see below). I assume that predominantly hyperplasia herein is mainly from an increased rate of cell birth.

Beyond being an inclusion criterion herein, this histologic feature of predominant hyperplasia is a self-supporting status and a robust endpoint in a gland. It is not simply a small or brief step towards progression to adenoma or cancer.

Of course, hyperplasia in a hormone-secreting gland is not uncommon in pathology. Predominant hyperplasia is also a fundamental process in many examples of excess. Furthermore, primary or secondary hyperplasia may progress to nodules, adenomas, and occasionally cancers (Arnold A 2011; Qureshi IA, Khabaz MN, et al 2015).

Distinguishing theme: Predominant hyperplasia as the cause of hormone over-secretion

I focus upon the process of hyperplasia and increased gland size, but hyperplasia also has a close relation or coupling with hormone over-secretion. The hyperplastic gland tissue must be the source of over-secreted hormones in these 5 syndromes, because hyperplasia is the predominant and stable tissue type in the gland. Some other hereditary syndromes of primary hormone excess differ from these five insofar as either normal-appearing tissue, or small or large nodules, adenoma, or cancer can predominate in the gland and can be the main source of over-secreted hormone (Supplementary Table S3 and Supplementary Table S4).

The 5 over-secreted hormones in these 5 hyperplasia syndromes represent 3 distinct categories of chemical: steroid, iodo-thyronine, and polypeptide. Their biosynthetic pathways are specific to their chemical structure and to the differentiated cell of secretion for each. Even the mechanisms of final “secretion” or exit from the cell differ among some of the 3 (Spat A, Hunyady L 2004; Rizo J, Sudhof TC 2012; Miot F, Dupuy C 2013).

The partial contributions to total over-secretion of hormone may be divided among broad functions within the mutated and over-secreting cell. First, a high basal release rate may be attributable to increased number of secreting cells. The enlarged gland may be over-secreting even despite a lower than normal secretion rate per cell (Assie G, Libé R, et al 2013). Among the 5 syndromes reviewed here, I estimate that the hyperplastic mass is typically increased over normal by 3–10 fold and is one major if not the principal determinant of the total amount of hormone secretion (Supplementary Table S-2).

Second, there may be increased basal secretion rate per cell (Brown EM, LeBoff MS, et al 1987); this is supported by high basal cyclic AMP level per cell in vitro with activating mutations of the TSH-R or the LH-R.

Third, some part of the over-secretion may be dependent on a mutant protein’s responsivity to its normal extracellular regulator ((Pearce SHS, Bai M, et al 1996). However, among the syndromes here, most of the extracellular ligands of the mutated molecules are down-regulated in serum by the feedbacks in their syndrome (expressed as high Ca++, low TSH, low LH, low FSH, and low K+, respectively; excepting CG, which is not down-regulated).

Distinguishing theme: The causative mutated molecule is a sensor in the plasma membrane

Four of five syndromes examined here are from germline mutation of a gene (CASR, TSHR, LHR, FSHR) that encodes a GPCR in the plasma membrane (Vassart G, Costagliola SG 2011; Lefkowitz RJ 2013), and mediates response to an extracellular ligand. The activating mutations of the GPCR subfamily of receptors for gonadotropins (TSR, LH, FSH) are modeled mainly within their 7 transmembrane loops. The CASR mutations in NSHPT cause nactivation of the CaS-R protein and model mainly to an extracellular domain of the CaS-R. The focus of germline mutations among these four GPCRs reflects that members of this largest of all gene families can sense highly diverse extracellular ligands, that they may transduce to diverse differentiated functions, and that their response may include hyperplasia (Lefkowitz RJ 2013; Katrich V, Cherezov V, et al 2013).

KCNJ5 encodes Kir3.4, a membrane-bound protein that functions as a direct sensor for extracellular K+ (Spat A, Hunyady L 2004; Choi M, Scholl UI, et al 2011); its structure as a membrane channel is not related to the GPCRs (Hibino H, Inanobe A, et al 2010).

Thus, each of the 5 mutated genes in these 5 syndromes encodes a plasma membrane protein that senses an extracellular regulator (O’Hayre M, JV, Kufeva I, et al 2013; Vogelstein B, Papadopoulos N, et al 2013).

Distinguishing theme: Each of 5 mutated sensors regulates a downstream pathway

This review included three mutation-directed pathways, immediately downstream of sensing for a serum factor (Figure 1). These pathways can be grouped narrowly as transducing information from the plasma membrane to an adjacent intracellular messenger. They transduce from plasma membrane G-protein coupled receptor (GPCR) to cyclic AMP, or from GPCR to inositol phosphates, or from plasma membrane K+ channel to cytoplasmic Ca++.

Figure 1.

Overview of parts of the signaling pathways of the five mutated proteins in the 5 syndromes of this review. The mutated K+ channel (or Kir3.4) is shown with abnormally decreased ion selectivity of its mutation, so that fluxes of K+ and Na+ are in directions reversed from normal. Mutated proteins causing syndromes of this review are shown in red. Early downstream parts of each of three pathways are highlighted by a different background color. The pathway from Gx divides and includes a large plus or minus sign to illustrate that the CaS-R has opposite downstream effects in the parathyroid cell versus in the C-cell. By mostly unknown mechanisms, the four pathways likely converge downstream to regulate secretion and hyperplasia.

Abbreviations: G-protein coupled receptor GPCR; Calmodulin Calmod; Calcium-calmodulin dependent protein kinase CaMK; Ion channels K or Ca; Phospholipase C PLC; Sigma subunit of AP2S1 AP2σ1; Adenylyl cyclase Ad Cy; Ligand L; Heterotrimeric stimulatory G-protein Gs; Heterotrimeric G-protein other than Gs Gx; GTP-binding protein modulator of Kir3.4 M; Phosphatidyl inositol diphosphate PIP2; Inositol triphosphate IP3; Phospho-diesterase PDE; Protein kinase A catalytic subunit A PK; Regulatory inhibitory subunit 1A of PKA R; Voltage of plasma membrane V.

The CaS-R on the parathyroid cell transduces hypercalcemia through Gq and/or Ga11, to activate phospholipase C, and thereby to raise inositol phosphates and to mobilize Ca++ from stores in the cytoplasm (Wettschureck N, Lee E, et al 2007; Conigrave AD, Ward DT 2013; Brown EM 2013; Hillenbrand M, Schori C, et al 2015; Cocco L, Follo MY, et al 2015; Nesbit MA, Hannan FM, et al. 2013B ). Lowering of extracellular Ca++ or loss of function mutations of the CaS-R as in NSHPT stimulate secretion and hyperplasia in the parathyroid cells.

Unlike the effect of rising Ca++ to inhibit secretion of PTH, a rise of extracellular Ca++ acts through the CaS-R of thyroidal parafollicular C-cells to stimulate secretion of calcitonin (Garrett JE, Tamir H, et al 1995; McGehee DS, Aldersberg M, et al 1997). It may not, however, cause hyperplasia of C-cells (Conte-Devolx B, Morlet-Barla N, et al 2010). The C-cell may also respond to Ca++ in part through a plasma membrane Ca++ channel (Kantham L, Quinn SJ, et al 2009). Overall, parathyroid cells and C-cells have contrasting hormone-secretory responses to serum calcium, with contrasts that are transduced at unknown steps.

The normal TSH-R transduces both secretion and growth in the thyrocyte mainly through Gsa and rise of cyclic AMP (Vassart G 2010; Kleinau G, Neumann S, et al 2013). However, TSH-R transduction of secretion and hyperplasia has also been reported through Gq/G11 (New DC, Wong YH 2007: Kero J, Ahmed K, et al. 2007). Similarly, the normal LH-R transduces a rise of serum LH mainly through Gs and cyclic AMP. D578H, the most severe activating human mutation of LHR, caused in vitro not only much higher basal cyclic AMP than other mutations but also much higher inositol phosphates, suggesting transduction also through a G-protein other than Gs (Boot AM, Lumbroso S, et al 2011). Lastly, the normal FSH-R transduces mainly through Gs and cyclic AMP. However, it also can transduce through different G-protein(s), causing rises of inositol phosphates and Ca++ in cytoplasm (Thomas RM, Nechamen CA, et al 2011). Normally cyclic AMP has potential to transduce to any of three major signaling pathways that start with one among the following molecules: protein kinase A, the guanine nucleotide exchange factor EPAC, and ion channels (Sassone-Corsi P 2012).

Kir3.4 is one of 4 G-protein-coupled Inward Rectifying K+ channels; therefore, it is also termed GIRK4. It can bind directly to a cytoplasmic modulator, such as the beta-gamma portion of a heterotrimeric G-protein or RGS (regulator of G-protein signaling) (Wickman KD, Iñiguez-Lluhl JA, et al 1994; Zhou H, Chisari M, et al 2012; Luscher C, Slesinger PA 2010; Velarde-Miranda C, Gomez-Sanchez EP, et al 2013; Bollag WP 2014). On the aldosterone cell, rise of extracellular K+ or influx of Na+ depolarizes the plasma membrane; this opens a plasma membrane Ca++ channel as a major transduction step towards aldosterone secretion (Velarde-Miranda C, Gomez-Sanchez EP, et al 2013; Bollag WP 2014). Effectors downstream from the rises of cytoplasmic Ca++ in the aldosterone-secreting cell may include calmodulin and several calcium calmodulin-dependent kinases (Spat A, Hunyady L 2004; Bollag WP 2014).

The mechanisms for sharing predominating hyperplasia are not known and represent an important topic for future studies. For e xample, hyperplasia can have unique features in diverse other settings, such as normal expansion of cartilage in the embryo or reversible development of the breast for lactation, (Hassiotou F, Geddes D 2013; Kozhemyakina E, Lasser AB, et al 2015).

Distinguishing themes: features within the hyperplasia group versus in 2 other groups with lower or higher histologic grade

Defining three groups for comparisons:

These 5 syndromes (the “hyperplasia” group) have important shared features that suggest both universal and also distinguishing aspects in their pathophysiology. Insights about their distinctinguishing aspecs can derive from comparison to different groups with hereditary primary excess of hormones (Supplementary Table S-1; and Tables S-3 – S-6). We compare hyperplasias to another group with primary and predominant over-secretion of hormones but little or no hyperplasia (abbreviated as the “over-secretion” group) (Marx SJ 2014) (Supplementary Table S-4 & S-6; an example is FHH. A second comparison group is dominated by adenomas or cancers (the “neoplasia” group) (Supplementary Table S-1, S-3, S-5 & S-6); an example is MEN1. The three groups form a continuum among three distinct histologic grades. Furthermore, the variables for comparison are organized for a yes or no entry, with the result that all comparisons are from simple integers.

Progression to neoplasia:

Hyperplasia sometimes (5 of 5 syndromes) progresses to nodules or other neoplastic features (Table 2) but oversecretion rarely does (1 of 6 syndromes; P<0.02; Table S-6B). This supports the observations many other primary hyperplastic tissues (whether or not they over-secrete a hormone) have an increased likelihood of progression to neoplasic stages (Gorgoulis VG, Vassiliou LV, et al Nature. 2005; Barcellos-Hoff ME, Lyden D, et al 2013).

Expression as neoplasia in sporadic tissue:

Capability to cause sporadic neoplasia is expressed by some hyperplasias (3 of 5) (Supplementary Table S-7) and by some oversecretions (1 of 5; P=0.53).. Neoplasias do this more consistently than hyperplasias (18 of 19; P<0.05).

Expression as tumor multiplicity:

In the hyperplasia grouip, an underlying germline mutation is rarely expressed as tumor in multiple tissues (0 of 5); in the neoplasia group, multiplicity is expressed in 14 of 20 syndromes (the two frequencies differ; P<0.02; Table S-6C).

Focus of mutant functions is among plasma membrane sensors:

Another difference for the hyperplasia group is the focus of all mutant gene functions among plasma membrane sensors (5 of 5 functions) versus one such gene function (RET) in the neoplasia group (1 of 18; P<0.0002; Table S-6E)). The functions of most causative genes in the neoplasia group are incompletely understood. It seems that functions of the mutated genes in the neoplasia group are mainly outside of the sensor-related cluster, and they probably contribute to hyperplasia and cancer through other pathways (Agarwal SK, Mateo C, et al 2009; Huang J, Gurung B, et al 2012; Vogelstein B, Papadopoulos N, et al 2013; Mulligan LM 2014; Dahia PM 2014).

Major clinical and molecular themes in the hyperplasia group help to distinguish it from the two other comparison groups and have strengthenedits robust identity.

The consistent sensor focus of the five mutant proteins on the background of this robust identity suggests that this abnormal biochemical focus is the cause of predominant hyperplasia. Since this mutated sensor might enhance cell numbers exponentialy, there might be limits to the capacity of cell numbers to expand. Alternately I speculate that one or more members of a downregulating network is expressed as a counterbalance. The arrestins are but one well-identified downregulating system for GPCRs, but others could be operational herein (Luttrell LM, Gesty-Palmer D 2010). It will be interesting to explore further the relation between these membrane sensors and predominant hyperplasia.

Abbreviations:

CaS-R

calcium sensing receptor

GPCR

G-protein coupled receptor

CNT

congenital neonatal thyrotoxicosis

FHH

familial hypocalciuric hypercalcemia

FMPP

familial male-limited precocious puberty

HAIII

hyperaldosteronism type III

MAH

micronodular adrenocortical hyperplasia

MEN

multiple endocrine neoplasia

NSHPT

neonatal severe primary hyperparathyroidism

OHSS

hereditaryovarian hyperstimulation syndrome

PPNAD

primary pigmented micro-nodular adrenocortical disease