Unusual Characteristics and Variable Expressivity in a Brazilian Family with Cherubism

Abstract

Cherubism is a rare genetic condition characterized by a bone nonneoplastic disease. We aimed to report a 6-year-old girl with cherubism presenting similar cases in the maternal family. However, her mother and grandmother seemed to be asymptomatic. The patient had an enlarged and asymmetric jaw with multiple enlarged cervical lymph nodes that increased in size with time. Sanger sequencing revealed a heterozygous mutation in exon 9 of SH3BP2 not only in the patient but also in her mother. Thus, we observed a variable expression and a probably reduced penetrance within the family, as well as unusual characteristics of the patient (in this case, the asymmetrical involvement of the jaw).

Introduction

Cherubism is a rare autosomal-dominant condition caused by a mutation in SH3BP2 gene that was first described in 1933 by Jones. ^{1 2 3 4} However, the term “cherubism” started to be used only a few years later due to the similarity with the cherubs depicted in the Renaissance art. ⁵ Cherubism is a bone nonneoplastic disease, which usually begins in childhood and affects equally children of both genders and different ethnicities. ^{6 7 8}

In cherubism, bone tissue is replaced by a fibrous cell tissue containing giant multinuclear cells, which leads to an increase in size especially of the maxilla and mandible. However, other findings may be present. ^{9 10 11}

We report on a Brazilian family with cherubism presenting unusual features (asymmetrical involvement of the jaw) and several affected individuals, but probably with reduced penetrance and variable expressivity. The institutional ethics committee has approved this study, and this project allows the use of patient images and data.

Case Report

The proband was the first daughter of young and nonconsanguineous parents. She was 6 years and 9 months old girl who came to evaluation at the hospital through a referral made by a general practitioner from a public health facility due to clinical suspicion of cherubism on medical examination. There was a description of similar cases in the maternal family. However, her mother and grandmother seemed to be asymptomatic. One cousin diagnosed with cherubism (the individual with “*” in the family pedigree) underwent surgery at the age of 19 years due to the vital mandible increase and airway involvement ( Fig. 1 ).

Fig. 1.

Pedigree of the family showing the individuals presenting cherubism. The asterisk represents a maternal cousin who has a more severe expression of the disease. Below you can see the sequencing of the patient and her parents, showing that she and her mother had the SH3BP2 variant (NG_011609.1:g.43560C > T, NM_001122681.1:c.1253C > T, rs121909146). However, her mother was asymptomatic (# indicates the individuals who have undergone molecular evaluation).

The patient was a twin from a diamniotic and dichorionic pregnancy, and her sister did not present any symptoms of cherubism. Further, she also had two healthy half-sisters from the mother's previous marriage. Her pregnancy was uneventful and the mother denied the use of medicines, with no history of vaginal bleeding or contractions. She only referred to smoking (five cigarettes/day) and rejected the intake of alcohol or the use of illicit drugs.

The child was born by cesarean section at 36 weeks and 3 days of gestation, measuring 47 cm (−1.10 standard deviation [SD]), weighing 2,330 g (−2.08 SD), with a head circumference of 32 cm (−1.90 SD) and an Apgar score of 9 at the fifth minute. Her newborn screening was normal. The child was discharged with her mother from the hospital. The patient had an episode of bronchiolitis at 1 month of age and needed to be hospitalized. As for neuropsychomotor development, it was appropriate: she sat alone at 5 months, walked without support at 11 months, spoke her first words at 9 months, and made use of diapers until 2 years. The parents had noticed her mandible increase at 4 year old. She also had multiple enlarged cervical lymph nodes that increased in size with age.

On physical examination, at the time of 6 years and 9 months, the height of the child was 116 cm (−0.73 SD), the weight was 17.5 kg (−1.77 SD), and the head circumference was 51 cm (−0.20 SD). She did not have any difficulty in breathing or eating. We observed a prominent forehead, bilateral epicanthal folds, broad nasal root and tip, high arched palate, and enlarged space between the first and second toes bilaterally. Additionally, it was observed that there was an increase in the mandibular region, which had an inconsistency and was not symmetrical, being more pronounced on the left. Hardened lymph nodes were also palpated in the cervical region. She did not present gingival hyperplasia, or café au lait spots ( Fig. 2 ).

Fig. 2.

Appearance of the patient at the age of 6 years and 9 months. Note especially the increase of the mandibular region, which had a hardened consistency (A – C) . It is noteworthy that this increase in size was not symmetrical, being more pronounced on the left.

Her father noticed that her teeth were falling out when they became longer as compared with her twin sister.

A dental examination showed an enlarged jaw, mainly in the left, which seemed to bilaterally limit the position of the teeth in the upper and lower dental arches. However, the patient did not have a crossbite. The mother noticed that the patient had often been sleeping with her mouth open ( Fig. 3 ).

Fig. 3.

Intraoral appearance showing the increased mandibular growth, mainly at left (A – C) . However, the patient did not present a cross-bite. In the panoramic radiograph of the face (D) . Multilocular bilateral expansive images can be seen along with absence of some primary teeth, as the two lower central incisors, and distal inclination of germs of others, as the lower first permanent molars, probably due to the osteolytic lesions (D) .

Bilateral multilocular expansive images were observed in the orthopantomogram. The patient had all the primary teeth, except the two lower central incisors and the second lower molar at left. All buds of the permanent teeth were present. However, distal inclination of the lower first molar tooth buds and mesial inclination of the lower second molar tooth buds were verified, probably because of the osteolytic lesions and distal second lower molar root resorption ( Fig. 3 ). Three-dimensional reconstructed face computed tomography showed signs of marked expansion and bilateral remodeling of the mandible, promoted by large cystic formations and multiloculated bone gaps, with marked cortical thinning. In some places, areas with bone cortical rupture were noticed. Cystic structures and locations were filled with soft tissue attenuating material. The lesions affected the horizontal and ascending branches of the mandible on both sides, partially preserving the body and mandible condyles. There were no lesions on the maxilla ( Figs. 4 and 5 ).

Fig. 4.

Face computed tomography of the patient at the age of 11 years and 9 months revealing bilateral and marked expansion of the mandible, with malalignment of several teeth (A – D) .

Fig. 5.

Three-dimensional reconstructed face computed tomography showing marked expansion and bilateral remodeling of the mandible, promoted by large cystic formations and multiloculated bone gaps (A – F) .

The ophthalmological evaluation did not show any abnormalities. The patient evolved with an accentuation of the mandibular volume and asymmetry, being higher on the left side. She did not present any symptoms related to an increase mandibular volume (the primary concern was aesthetic). The patient chose not to go under oral and maxillofacial surgery at the age of 14 (the procedure was conservative).

Results

High-resolution GTG-banding karyotype performed from a peripheral blood sample was normal (46,XX). DNA from both patient and parents was isolated from blood samples using a salting-out method. ¹² Primers were designed for all exons of the SH3BP2 gene, according to the National Center for Biotechnology Information (NCBI) reference sequence (NG_011609.1) with Primer3 ( http://frodo.wi.mit.edu/primer3/ ). Polymerized chain reaction was performed in 25 μL reaction volume containing 100 ng of genomic DNA, 0.4 mmol/L of deoxyribonucleotide triphosphates (dNTPs), 1.5 mmol/L of MgCl ₂ , 0.4 μmol/L of each primer, and 1 U of Taq DNA polymerase. Unincorporated primers and dNTPs were removed via the ExoSAP-IT protocol according to the manufactureŕs instructions (Applied Biosystems by Thermo Fisher Scientific). The DNA sequencing was performed on an ABI-PRISM 3130 genetic analyzer, and sequences were analyzed with a Chromas Lite program.

Sanger sequencing analysis of exon 9 revealed a heterozygous variant in the patient's electropherogram (NG_011609.1:g.43560C > T, NM_001122681.1:c.1253C > T, rs121909146). The variant detected C > T transition that leads to an amino acid substitution from proline to leucine (Pro418Leu) [accession ID at ClinVar ( http://www.ncbi.nlm.nih.gov/clinvar ): SCV000996316.1]. Also, the sequencing of this exon in the mother's sample showed the same heterozygous variation, indicating that the mutated allele was inherited through the maternal lineage ( Fig. 1 ).

Discussion

The clinical and radiological findings of the family along with the molecular evaluation were consistent with the diagnosis of cherubism. Cherubism is characterized by the symmetrical and painless growth of the jaw bones and retraction of the lower eyelid, exposing the sclera below the iris, giving the impression of an “upward glance.” The involvement of another bone is considered rare. ^{13 14} The bone lesion usually begins in childhood and tends to increase progressively until puberty. ^{15 16} Most of the cases resolve spontaneously in adult life. ^{9 15 17}

Cervical and submandibular enlarged lymph nodes are frequent and may develop before bone lesions. ^{10 18} Besides, dental anomalies may be present. ¹⁵ However, the inconsistency of clinical manifestations may be broad. ¹¹ In most cases, cherubism is a benign condition characterized mainly by abnormalities with cosmetic impairment. However, there are more severe forms that can lead to respiratory distress, visual changes, swallowing disorders, and maybe even fatal. ^{6 16} In our analysis, her asymmetrical jaw presentation is considered unusual ( Table 1; Fig. 2 ).

Table 1. Description of the family cases of cherubism described in the literature compared with ours.

Authors	Affected individuals	Country	Unusual clinical findings	Molecular analysis
Hitomi et al 40	Proband, mother, brother	Japan	No	–
Mangion et al 41	Family 1: proband, brother, two cousins Family 2: proband, father, two uncles, one aunt, one cousin	England	No	Genome-wide linkage search suggested that the gene of cherubism was localized at chromosome 4p16.3
Von Wowern 8	Family 1: proband, daughter, and two cousins Family 2: proband, brother, nephew, and three cousins Family 3: proband, mother, uncle Family 4: proband, brother, mother	Denmark	No	–
Ongole et al 42	Proband, brother	India	No	–
Petkovska et al 43	Proband, two sisters, father	Kuwait	No	–
Li and Yu 6	Proband, sister, niece	China	No	SH3BP2 , exon 9 c.1517A > G, p.Asp419Gly
Carvalho Silva et al 13	Proband, sister, son, niece	Brazil	No	–
de Lange et al 35	Proband, mother, cousin	Turkey	Asymptomatic aunt carrying the mutated gene	SH3BP2 , exon 9 c.1513C > A, p.Pro418Thr
Mortellaro et al 44	Proband, father	Italy	Father with unilateral radiological findings	–
Muthuraman and Srinivasan 17	Proband, mother	India	No	–
Sekerci et al 36	Proband, sister, and six people in the mother's family	Turkey	Asymptomatic mother carrying the mutated gene	SH3BP2 , exon 9 c.1244G > A, a p.Arg415Gln, rs121909149
Tsodoulos et al 18	Proband, mother, maternal grandmother	Greece	The proband presented a very severe form of the disease	–
Singh et al 30	Proband, mother	India	No	SH3BP2 , exon 9 c.1258G > A, a p.Gly420Arg, rs28938170
Argyris et al 45	Proband, mother, maternal grandfather, son, and daughter	United States	Odontogenic tumorous proliferations in the anterior portion of the mandible with expansion into the premolar area; persistent phenotype after puberty	SH3BP2 , exon 9 c.1244G > C, a p.Arg415Pro, rs121909149
Our family	Proband, maternal great-grandfather, brothers of the grandmother, and maternal cousins	Brazil	At least mother and probably grandmother, both asymptomatic, carrying the mutated gene; variable expressivity and reduced penetrance in the family	SH3BP2 ; exon 9 c.1253C > T, a p.Pro418Leu, rs121909146

^aNM_003023.4.

A characteristic radiological finding of the disease is the bilateral multilocular radiolucent aspect, as observed in the orthopantomogram of our patient. ¹³ This result may also reveal the presence of dental malpositioning, premature tooth loss, and gingival hypertrophy. ¹⁹ Cherubism also has different types of classification. The two most commonly used are those proposed by Kalantar Motamedi and Raposo-Amaral et al, which are based on the location of the bone lesions and their severity. ^{20 21}

The patient did not undergo a biopsy and histopathological analysis of the mandible and maxilla lesions. However, the histopathologic findings described among patients include nonneoplastic fibrotic lesions with several multinuclear giant cells, cysts, and an increase in osteoid and newly formed bone matrix in the periphery. ^{7 10}

The treatment of cherubism usually is conservative, as happened with our patient, considering that in most cases, the regression usually occurs after puberty and is resolved spontaneously. ^{9 17} The lower the degree of disease involvement, the earlier its stabilization and regression tend to occur. ⁸ Despite this, regular follow-up is advised. ¹⁵ In some cases, specially the most severe ones, like that of the patient's cousin, surgical procedures may be necessary, as well as treatment of dental manifestations. Usually, these consist of surgical recontouring, curettage, and orthodontic surgery of malaligned teeth. In some situations, a surgical procedure is commonly performed due to aesthetic reasons. ¹⁵ In the case of the patient's cousin, the main indication for surgery was the respiratory dysfunction presented by her. She had a severe mandible involvement.

It is well known that mutation in the SH3BP2 gene cause cherubism. ²² This gene encodes a protein whose function is still unclear. ²³ However, some studies suggest that it is required to optimize signaling through B cells and macrophage activation in the immune system. ^{24 25} Additional several evidence indicates that the SH3BP2 gene is an integral component of a signaling pathway that activates the nuclear factor of activated T-cells, an osteoclastogenic mediator and primary “switch” of osteoclastogenesis. ^{26 27}

The SH3BP2 gene region commonly associated with cherubism is composed of six amino acids encoded by exon 9. ^{1 28 29} To date, around 13 different pathological variants have been described. ²³ These variants result in the alteration of a recognition site for the binding of the tankyrase. Further, it leads to an overexpression of a protein that induces osteoclast formation and secretion of tumor necrosis factor-α. ^{30 31} The SH3BP2 variant found in our patient and her mother leads to an amino acid (cytosine) alteration not only into thymine, but also into both adenine and guanine, all leading to a distinct amino acid exchange (Pro418His and Pro418Arg). ^{32 33 34} Although each nucleotide translates into a different amino acid, all modifications found on that same spot of exon 9 entail into a phenotype of cherubism.

Some familial studies presenting cherubism have been previously described ( Table 1 ). In our case, both the patient and the mother had the same SH3BP2 variant; only the daughter expressed the phenotype of cherubism. Similar incidents have been reported previously. ^{35 36} Reduced penetrance happens when some individuals have specific variants and do not show the clinical features of the disease, while other individuals carrying the same variants exhibit the symptoms. These phenomena usually occur when disorders have an autosomal-dominant trait, as is the case of cherubism. ⁷ Cherubism has 100% penetrance in males and 50 to 70% in females. ^{37 38} However, expression of symptoms and the possibility of a historical artifact have been observed due to misinterpretation in clinical investigation in adult patients with a mild form of cherubism, which may have contributed to the misconception of reduced penetrance. ⁷ Moreover, the frequent regression of signs and symptoms after puberty is noteworthy within the evolution of the disease. Perhaps, hormonal factors may be involved and explain the reduced penetrance observed in females with cherubism. Another possible mechanism is the involvement of inflammation through the TLR-MYD88-NF-kB signaling axis. The cherubism mice model showed hyperresponsiveness in the TLR-MYD88 pathway to PAMPs (pathogen-associated molecular patterns) and DAMPs (damage-associated molecular patterns), which stimulates autoinflammation in jaw development. Other members of the patient's family could have different degrees of response to PAMPs and DAMPs that may imply in additional factors to explain variable expressivity. Moreover, the response to DAMPs after puberty could explain age-dependent regression. ³⁹ All these factors may elucidate underlying mechanisms associated with variable expression of cherubism phenotype.

Conclusion

Cherubism is a rare genetic condition with a small number of affected families reported in the literature. In this report, we observed a family in which cherubism was a recurrent condition with several family members. However, the classical autosomal-dominant pattern of inherence was not observed probably due to the non-Mendelian genetics pattern, such as reduced penetrance and/or variable expression. The necessary information related to the genetic factors involved in cherubism is essential for the vital genetic counseling of the patients and their families. Further studies are needed for better understanding of the molecular mechanisms of cherubism that could explain why this variation in penetrance and expressivity happens in a different manner.

Funding Statement

Funding This work was funded by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).