Insulin resistant diabetes mellitus in a girl with mild Rabson-Mendenhall syndrome: efficacy of sodium glucose co-transporter 2 inhibitor

Abstract

We report a beneficial effect of a sodium glucose co-transporter 2 (SGLT2) inhibitor in the management of insulin resistant diabetes mellitus (IRDM) in a Japanese girl with mild Rabson-Mendenhall syndrome (RMS). At 10 2/12 years of age, she was referred to us because of glucosuria, and was found to have marked acanthosis nigricans and RMS-like facial features such as proptosis, large ears, full lips, and gingival hypertrophy, but not other clinical features frequently found in RMS. At 11 9/12 years of age, her blood HbA1c level, though it remained ~ 6.5% until then, increased to 7.9% with pubertal development. She was treated with an SGLT2 inhibitor and metformin, which ameliorated overt hyperglycemia in the afternoon and the evening (postprandial time) as well as obvious hypoglycemia in the early morning (before breakfast), and reduced her blood HbA1c to 5.5%. Whole exome sequencing revealed probably disease-causing c.2465 T > C:p.(Leu822Pro) of paternal origin and c.3038C > T:p.(Pro1013Leu) of maternal origin in INSR. These findings imply the usefulness of SGLT2 inhibitor in the treatment of IRDM. It is likely that SGLT2 inhibitor mitigated hyperglycemia by increasing the urine glucose excretion and prevented severe hypoglycemia probably because of attenuated hyperinsulinemia in the absence of overt hyperglycemia.

Introduction

Insulin receptor is a transmembrane protein composed of extracellular α subunits with an insulin binding site and transmembrane β subunits with a tyrosine kinase domain [1]. It is encoded by insulin receptor gene (INSR) and plays a crucial role in the insulin signaling and glucose metabolism [1]. Thus, heterozygous relatively severe INSR loss-of-function (LOF) variants result in type A insulin resistance syndrome (TAIRS) (OMIM #610549), whereas biallelic relatively mild and relatively severe LOF INSR variants lead to Rabson-Mendenhall syndrome (RMS) (OMIM #262190) and Donohue syndrome (DS) (OMIM #246200), respectively [2, 3]. Clinical findings in these syndromes include insulin resistance, fetal growth restriction, acanthosis nigricans, and hirsutism. Furthermore, RMS and DS are frequently associated with characteristic facial appearance, postnatal growth failure, and enlarged genitalia, and DS is also frequently accompanied by lipodystrophy. Thus, clinical findings become more severe in order of TAIRS, RMS, and DS. Indeed, patients with TAIR and RMS can survive through childhood, whereas those with DS usually die during infancy.

Insulin resistant diabetes mellitus (IRDM) is also commonly observed in these syndromes [2]. To date, several therapeutic interventions have been attempted for IRDM, including dietary management, insulin sensitization, insulin therapy, metformin treatment, and recombinant human insulin-like growth factor-1 administration [4]. However, the effects of these therapies remain unsatisfactory.

Here, we report a Japanese girl with mild RMS who developed IRDM with puberty, and discuss the efficacy of a sodium glucose co-transporter 2 (SGLT2) inhibitor in the management of IRDM.

Case report

This Japanese girl was born to non-consanguineous parents at 39 weeks of gestation after an uncomplicated pregnancy and delivery. At birth, her length was 52.0 cm (+ 1.8 SD), and her weight 2.92 kg (–0.1 SD). Allegedly, she stayed quiet in infancy, and remained inactive in the early morning before breakfast in her childhood, although she became active after breakfast. At six years of age, she was diagnosed with attention deficit hyperactivity disorder, and was placed on methylphenidate until nine years of age.

At 10 2/12 years of age, she was referred to us because of glucosuria at the time of yearly school health check. Physical examination revealed a prepubertal girl with marked acanthosis nigricans on her neck, axilla, and limb joints (Fig. 1a), and RMS-like facial features such as proptosis, large ears, full lips, and gingival hypertrophy. Her growth pattern was normal (Fig. 1b). Blood HbA1c was 6.3% (Fig. 1c), and oral glucose tolerance test (OGTT) revealed borderline glucose intolerance and markedly high serum insulin values (Fig. 1d). Continuous glucose monitoring (CGM) showed hyperglycemia in the afternoon and the evening (after lunch and supper) and hypoglycemia in the nighttime, especially early in the morning (before breakfast) (Fig. 1e). An insulin receptor antibody was negative. Thus, she was suspected to have RMS, and was placed on a periodical follow-up.

Fig. 1.

Clinical findings of this patient (a–e) and the parents (f). a Acanthosis nigricans on the neck (middle) and the axilla (right). B Growth chart plotted on the standard growth curves of Japanese girls. b, Tanner breast stage; and P, Tanner pubic hair stage. c Change in blood HbA1c value and therapeutic interventions. d OGTT data at 10 2/12 years of age (upper), at 11 9/12 years of age before treatment (middle), and at 12 8/12 years of age treated with dapagliflozin and metformin (lower). e CGM data at 10 2/12 years of age (upper), at 11 9/12 years of age before treatment (middle), and at 12 8/12 years treated with dapagliflozin and metformin (lower). f Blood HbA1c values and OGTT data in the parents

At 11 9/12 years of age, her blood HbA1c level, though it remained ~ 6.5% until then, increased to 7.9% with pubertal development (breast at Tanner stage 3 and pubic hair at Tanner stage 2) (Fig. 1c). Serum LH was 0.41 IU/L, FSH 2.22 IU/L, and estradiol 68.6 pg/mL. OGTT at that time indicated slightly worsened glucose intolerance (Fig. 1d), and CGM showed a marked fluctuation of glucose levels, with severe hyperglycemia (> 200 mg/dL) in the afternoon and the evening and obvious hypoglycemia (< 50 mg/dL) in the early morning (Fig. 1e). Thus, she was diagnosed with IRDM, and was treated with an SGLT2 inhibitor (dapagliflozin, 5 mg/day p.o.), which is approved for patients aged ≥ 10 years of age in US, EU, and other countries, under the support for a Specific Pediatric Chronic Disease after obtaining oral consent from the parents, followed by the addition of Metformin (500 mg/day p.o.) (Fig. 1b, c). This treatment successfully decreased her blood HbA1c to 5.5% and, though the OGTT data were grossly similar before and after the treatment (Fig. 1d), CGM revealed obviously stabilized glucose values, with markedly ameliorated hyperglycemia in the afternoon and the evening and low but stable glucose values in the nighttime (Fig. 1e). Furthermore, she became active immediately from the awaking time before breakfast.

Subsequent clinical course was uneventful. While she showed a slight and transient reduction in the body weight shortly after the administration of dapagliflozin (~ 1 kg) (Fig. 1b), she remained healthy with no episode of dehydration, urinary tract infection, or appearance of urine ketone bodies. Abdominal ultrasound studies at 12 2/12 years of age delineated no polycystic ovaries or organomegaly. On the latest examination at 13 4/12 years of age, she measured 151.6 cm (–0.5 SD), weighed 39.6 kg (–1.0 SD), and showed progressed pubertal development (breast at Tanner stage 4 and pubic hair at Tanner stage 3), although she had no menarche yet. She exhibited an RMS-like characteristic facial features and acanthosis nigricans but had no other clinical features frequently found in RMS such as hirsutism, prominent nipples, enlarged genitalia, and polycystic ovary [5]. At that time, her blood HbA1c was 6.4%.

Molecular studies

We performed whole exome sequencing (WES) for leukocyte gDNA samples of the patient and her parents, using SureSelect Human All Exon V6 (Agilent Technologies). Captured libraries were sequenced using NextSeq 500 (Illumina, San Diego, CA, USA) with 150 bp paired-end reads. Exome data processing, variant calling, and variant annotation were carried out as described previously [6], using Human GRCh38 (UCSC Genome Browser; http://genome.ucsc.edu/) as the reference genome. We extracted rare variants with minor allele frequencies of ≤ 0.01 in all the public and in-house databases utilized in this study, and performed in silico pathogenicity predictions for extracted rare variants by several tools. The databases and pathogenicity prediction tools are described in the legend for Fig. 2, together with their URLs.

Fig. 2.

INSR variants identified in this study. a The gDNA and cDNA structures of INSR and the positions of the c.2465 T > C:p.(Leu822Pro) (blue arrows) and c.3038C > T:p.(Pro1013Leu) (red arrows). The cDNA encodes a 1,382 amino acid protein containing two Receptor L domains, one Furin-like Cysteine-rich domain, three FNIII domains, and one Tyrosine kinase domain. b Electrochromatograms showing the c.2465 T > C substitution shared by this patient and her father (marked with blue asterisks) and the c.3038C > T substitution shared by this patient and her mother (marked with red asterisks). The primers utilized for c.2465 T > C are: forward, 5′-AAAAATGATGGTGATGGTGTCA-3′, and reverse, 5′-GGGTGGAGAATCTGTCCTTG-3′; and those for c.3038C > T are: forward, 5′-ATCCTCCAAGGATGCTGTGT-3′, and reverse, 5′-CACCCCCACTGGACTCAC-3′. c Absence of c.2465 T > C:p.(Leu822Pro) and c.3038C > T:p.(Pro1013Leu) in the public and in-house databases utilized in this study, and predicted pathogenicity of p.(Leu822Pro) and p.(Pro1013Leu) by in silico analyses utilized in this study. The URLs utilized are: (1) gnomAD (Genome Aggregation Database): http://gnomad.broadinstitute.org; (2) HGVD (Human Genetic Variation Database): http://www.hgvd.genome.med.kyoto-u.ac.jp; (3) 54KJPN (Whole-genome sequences of approximately 54,000 healthy Japanese individuals and construction of the highly accurate Japanese population reference panel): https://jmorp.megabank.tohoku.ac.jp; (4) CADD (combined annotation–dependent depletion): http://cadd.gs.washington.edu/score; PHRED scores of > 10–20 are regarded as deleterious, and those of > 20 indicates the 1% most deleterious; (5) Polyphen-2 Hum Var: http://genetics.bwh.harvard.edu/pph2; HumVar scores were evaluated as 0.000 (most probably benign) to 1.000 (most probably damaging); (6) SIFT (sorting intolerant from tolerant): http://sift.jcvi.org; Scores of ≤ 0.05 and those > 0.05 are assessed as damaging and tolerated, respectively; and (7) MutationTaster: http://www.mutationtaster.org (MutationTaster2, GRCh37/Ensembl 69); Alterations are classified as disease causing or polymorphisms, and the high scores of ~ 1.00 indicate the high probability of disease-causing variant or polymorphism

Consequently, WES revealed compound heterozygous missense variants of INSR (NM_000208.4), i.e. a paternally inherited c.2465 T > C:p.(Leu822Pro) and a maternally inherited c.3038C > T:p.(Pro1013Leu) (Fig. 2a), as confirmed by Sanger sequencing (Fig. 2b). Both variants were completely absent from the databases utilized in this study, and their pathogenicity was variably evaluated by the pathogenicity prediction tools utilized in this study (Fig. 2c). No other rare variant was identified in the insulin signaling pathway [7], under the assumption of Mendelian inheritance with complete penetrance by the trio analysis.

Discussion

We encountered a girl with glucosuria who was found to have severe acanthosis nigricans and marked hyperinsulinemia. Notably, she exhibited RMS-like facial features in addition to acanthosis nigricans but lacked other RMS-like clinical findings [5]. Thus, she would be diagnosed as having mild RMS. It should be pointed out, however, that she may manifest several features such as hirsutism, prominent nipples, genital enlargement, and/or polycystic ovary with pubertal development via an interaction between insulin and sex steroids in a later age [8].

Genetic studies revealed biallelic variants, c.2465 T > C:p.(Leu822Pro) of paternal origin and c.3038C > T:p.(Pro1013Leu) of maternal origin, in INSR of this patient, consistent with the mild RMS phenotype. Of these, the c.2465 T > C:p.(Leu822Pro) has been shown to affect autophosphorylation by a functional analysis [9]. Thus, the c.2465 T > C:p.(Leu822Pro) is assessed as "likely pathogenic", because it is positive for PS3 (well-established in vitro functional studies supportive of a damaging effect) and PM2 (absent from controls) [10]. Indeed, homozygosity for this variant has been reported in an infant with DS [9]. By contrast, the c.3038C > T:p.(Pro1013Leu) has not been evaluated functionally. Thus, the c.3038C > T:p.(Pro1013Leu) is assessed as "uncertain significance", because it is positive for PM2 alone. However, this variant has been identified in a girl with mild RMS phenotype, together with a pathogenic c.3720_3723delGTCT variant in a compound heterozygous condition [11]. Considering that RMS is caused by biallelic deleterious INSR variants, it is likely that the c.3038C > T:p.(Pro1013Leu) is a disease-causing variant.

The IRDM of this patient took place with pubertal development. This is consistent with the previous finding that the physical and endocrinological changes during puberty lead to a marked decrease in insulin sensitivity [12]. In support of this notion, such an occurrence of DM with pubertal development has also been reported in TAIRS and in other types of DM such as IRDM in SHORT syndrome, maturity-onset diabetes of the young, and 6q24-related DM [13–15].

Most importantly, the IRDM of this patient was well controlled by the SGLT2 inhibitor, while metformin treatment would have also contributed to the management of IRDM in this patient. Indeed, although she had severe hyperglycemia in the afternoon and the evening and overt hypoglycemia in the early morning, the SGLT2 inhibitor stabilized blood glucose levels throughout the day and improved her activity from early in the morning. As a consequence, her blood HbAc1 was normalized. It is likely that SGLT2 inhibitor mitigated hyperglycemia by increasing the urine glucose excretion and prevented severe hypoglycemia probably because of attenuated hyperinsulinemia in the absence of overt hyperglycemia. While insulin response during OGTT was grossly similar before and after the treatment, it is inferred that insulin secretary profile became less fluctuated after the administration of SGLT2 inhibitor as was blood glucose profile on CGM. Such beneficial effects of an SGLT2 inhibitor have also been reported in other patients with insulin resistance, such as TAIRS, RMS, and SHORT syndrome [13, 16, 17]. Furthermore, an SGLT2 inhibitor is known as an effective and easy-to-use drug because of the very low risk to cause hypoglycemia, as indicated by the lack of adverse events in this patient. Thus, an SGLT2 inhibitor could be an important option for the treatment of IRDM worsened with pubertal development in adolescent patients.

Author contributions

All authors made individual contributions to authorship. YM and HS performed molecular analyses. KK, YM, YF, and TO participated in the diagnosis and management of the case. YM and TO wrote the manuscript, with acritical input from YF and HS. All authors reviewed and approved the final draft.

Funding

This work was supported by Grants from Japan Agency for Medical Research and Development (AMED) (JP24ek0109760).

Data availability

The data that support the findings of this study are available from the corresponding author on reasonable request.

Declarations

Conflict of interest

Author Ogata T received lecture fees from JCR Pharmaceuticals Co., Ltd., and Novo Nordisk Pharma Ltd. The rest of the authors declare that they have no conflict of interest.

Ethical approval

This study was approved by the Institutional Review Board Committee at Hamamatsu University School of Medicine, and was performed after obtaining written informed consent.