Syndrome of Congenital Insulin Resistance Caused by a Novel INSR Gene Mutation

Mutations in the INSR gene result in rare inherited syndromes causing insulin resistance, such as leprechaunism (Donohue syndrome), Rabson-Mendenhall syndrome and insulin resistance type A. Leprechaunism is an autosomal recessive disorder associated with extreme insulin resistance that leads to hyperinsulinemia, impaired glucose homeostasis, fasting hypoglycemia and postprandial hyperglycemia. Impaired insulin action causes prenatal and postnatal growth retardation. Lipoatrophy, dysmorphic facies, hypertrichosis, macrogenitosomia and hypertrophy of internal organs are also present. A male infant with congenital insulin resistance was born at term after a normal pregnancy with a weight of 1905 g (<3 c), a length of 48 cm (<3 c), and an Apgar score of 10. Intrauterine growth retardation, transient hypoglycemia, pneumonia, urinary tract infection and heart defects [patent foramen ovale (PFO); patent ductus arteriosus (PDA)] were diagnosed after birth. At 5 weeks of age, he was admitted to the regional hospital with severe fever, diarrhea and dehydration. Hyperglycemia was observed (672 mg/dL), and insulin was administered. He was referred to a hospital at 7 weeks of age for suspected neonatal diabetes and hypertrophic cardiomyopathy. The physical examination revealed a loud systolic heart murmur, tachycardia, tachypnea, dysmorphic facies, hypertrichosis, acanthosis nigricans, hypotonia, swollen nipples and enlarged testicles. Glycemic fluctuations (50-250 mg/dL) were observed. The serum insulin concentration was high (maximum 1200 IU/mL) at normoglycemia. Ultrasound of the heart confirmed progressive hypertrophic cardiomyopathy. Leprechaunism was confirmed by genetic analysis of INSR, in which a novel c.320C>G; p. Thr107Arg homozygous missense mutation was found in exon 2.

[Donohue syndrome and use of continuous subcutaneous IGF1 pump therapy].

Donohue syndrome (DS), also called Leprechaunism, is the most severe form of insulin resistance associated with biallelic mutations in INSR gene (OMIM: 147670). The approximate incidence of this syndrome is 1 per 1000000 births. Patients are present with typical clinical features such as intrauterine growth retardation, facial dysmorphism, severe metabolic disturbances, hepatomegaly and hypertrophic cardiomyopathy. Most DS patients die within the first two years of life due to respiratory infections, severe hypoglycemia or progressive cardiomyopathy. Treatment options are limited and no specific therapy exist for DS. Given the similarities between insulin and insulin-like growth factor 1 (IGF-1) receptors, recombinant human IGF-1 (rhIGF-1) has been used to treat severe insulin resistance including DS.We report the case of a male patient with genetically confirmed Donohue syndrome, successfully treated with continuous subcutaneous IGF1 infusion via insulin pump. We observed improvement of glycemic control, liver function and cardiac hypertrophy regression following 15-month IGF1 therapy.

Management challenges of Rabson Mendenhall syndrome in a resource limited country: a case report.

OBJECTIVES: Rabson Mendenhall syndrome  (RMS) is a rare form of insulin resistance syndrome caused by insulin receptor mutation. In term of severity, it lies at an intermediate point on spectrum of insulin resistance with Donohue syndrome flanking the severe and Type A insulin resistance at the mild end. We are reporting a 3.5-month-old boy with RMS along with its management challenges in a resource limited country. CASE PRESENTATION: An infant presented at 3.5-month of an age with failure to thrive and fluctuating blood glucose level (hyperglycaemia and hypoglycaemia) along with clinical features of insulin resistance. He was found to have raised HbA1C, high insulin and C peptide level and a homozygous mutation in INSR gene c.1049C>T, (p.Ser350 Leu) confirming the diagnosis of RMS. He was managed with long-acting insulin (Detemir) along with frequent feeding. CONCLUSIONS: RMS in resource limited countries could be managed with frequent feeding along with insulin. Early diagnosis and management can improve long term outcome.

New classification and diagnostic criteria for insulin resistance syndrome.

This report of a working group established by the Japan Diabetes Society proposes a new classification and diagnostic criteria for insulin resistance syndrome. Insulin resistance syndrome is defined as a condition characterized by severe attenuation of insulin action due to functional impairment of the insulin receptor or its downstream signaling molecules. This syndrome is classified into two types: genetic insulin resistance syndrome, caused by gene abnormalities, and type B insulin resistance syndrome, caused by autoantibodies to the insulin receptor. Genetic insulin resistance syndrome includes type A insulin resistance as well as Donohue and Rabson-Mendenhall syndromes, all of which are caused by abnormalities of the insulin receptor gene; conditions such as SHORT syndrome caused by abnormalities of PIK3R1, which encodes a regulatory subunit of phosphatidylinositol 3-kinase; conditions caused by abnormalities of AKT2, TBC1D4, or PRKCE; and conditions in which a causative gene has not yet been identified. Type B insulin resistance syndrome is characterized by severe impairment of insulin action due to the presence of insulin receptor autoantibodies. Cases in which hypoglycemia alone is induced by autoantibodies that stimulate insulin receptor were not included in Type B insulin resistance syndrome.

Long-Term Effects of Metreleptin in Rabson-Mendenhall Syndrome on Glycemia, Growth, and Kidney Function.

CONTEXT: Rabson-Mendenhall syndrome (RMS) is caused by biallelic pathogenic variants in the insulin receptor gene (INSR) leading to insulin-resistant diabetes, microvascular complications, and growth hormone resistance with short stature. Small, uncontrolled studies suggest that 1-year treatment with recombinant leptin (metreleptin) improves glycemia in RMS. OBJECTIVE: This study aimed to determine effects of long-term metreleptin in RMS on glycemia, anthropometrics, the growth hormone axis, and kidney function. METHODS: We compared RMS patients during nonrandomized open-label treatment with metreleptin (≥ 0.15 mg/kg/day) vs no metreleptin over 90 months (5 subjects in both groups at different times, 4 only in metreleptin group, 2 only in control group). Main outcome measures were A1c; glucose; insulin; 24-hour urine glucose; standard deviation scores (SDS) for height, weight, body mass index (BMI), and insulin-like growth factor 1 (IGF-1); growth hormone; and estimated glomerular filtration rate. RESULTS: Over time, metreleptin-treated subjects maintained 1.8 percentage point lower A1c vs controls (P = 0.007), which remained significant after accounting for changes in insulin doses. Metreleptin-treated subjects had a reduction in BMI SDS, which predicted decreased A1c. Growth hormone increased after metreleptin treatment vs control, with no difference in SDS between groups for IGF-1 or height. Reduced BMI predicted higher growth hormone, while reduced A1c predicted higher IGF-1. CONCLUSION: Metreleptin alters the natural history of rising A1c in RMS, leading to lower A1c throughout long-term follow-up. Improved glycemia with metreleptin is likely attributable to appetite suppression and lower BMI SDS. Lower BMI after metreleptin may also worsen growth hormone resistance in RMS, resulting in a null effect on IGF-1 and growth despite improved glycemia.

INSR novel mutations identified in a Chinese family with severe INSR-related insulin resistance syndromes: A case report.

RATIONALE: Severe insulin receptor gene (INSR)-related insulin resistance syndromes (SIR) include Donohue syndrome (DS), Rabson-Mendenhall syndrome (RMS), and type A insulin resistance. The incidence of DS is about 1 in 4 million births. We identified novel INSR mutations (c.2246delG and c.2646 + 5G > A) in a patient with SIR, which expanded the variant spectrum and helped to improve the understanding of the diagnosis and treatment of this condition. PATIENT CONCERNS: A 10-year-old Chinese boy was admitted to the hospital for deepening skin color. He presented with growth retardation, peculiar facial features, acanthosis nigricans, hypertrichosis, extremely high insulin levels, fasting hypoglycemia, and postprandial hyperglycemia, Whole-exome gene testing suggested compound heterozygous mutations in INSR (c.2246delG and c.2646 + 5G > A). DIAGNOSIS: The diagnosis was SIR. What's more, based on the phenotypic and biographical results, this child did not present typical RMS and DS but rather an intermediate phenotype between the 2 conditions. INTERVENTIONS: On the basis of a sensible diet and exercise, the patient was prescribed metformin (250 mg) at breakfast and lunch, which was increased to 500 mg after 1 month. OUTCOMES: After 2 months of treatment, the patient's glycated hemoglobin (HbA1c) levels decreased to 6% but his insulin resistance did not improve significantly. LESSONS: In children who are not obese but with severe insulin resistance, growth retardation, hirsutism, and hyperglycemia, genetic testing should be performed for early diagnosis, active treatment, and follow-up.

Use of a Sodium-Glucose Cotransporter 2 Inhibitor, Empagliflozin, in a Patient with Rabson-Mendenhall Syndrome.

INTRODUCTION: Among the insulin resistance syndromes that lead to diabetes mellitus in young people, Rabson-Mendenhall syndrome (RMS; OMIM # 262190) is an autosomal recessive inherited disease caused by an insulin receptor mutation (INSR; 147,670). Due to the rarity and complexity of the disease, we have few therapeutic alternatives other than insulin with clinical studies with robust evidence. Some reports suggest the adjunct use of metreleptin, metformin, and pioglitazone with improved glycemic control, however, with results still unsatisfactory for the desirable glycemic targets for this age group. CASE PRESENTATION: We report a case of an 11-year-old patient who was diagnosed with RMS at 6 years of age, confirmed through genetic sequencing, with unsatisfactory glycemic control despite the use of >5 IU/kg/day of insulin, pioglitazone, and metformin. To optimize therapy, we used empagliflozin (SGLT2i) to correct hyperglycemia. With the use of the drug, we obtained a decrease of almost 3% in the value of glycated hemoglobin (HbA1c) and about 30% reduction in the total daily dose of insulin. DISCUSSION/CONCLUSION: In this specific case, considering the glycosuric effects independent of the functionality of insulin receptors (which in this case had partial activity due to the INSR gene mutation), an improvement in glycemic control was obtained, with optimization of HbA1c without documented or reported adverse effects. From this isolated case and understanding the pharmacokinetics of this drug class, the question remains whether it would be possible to use this treatment in other situations of SIR where we also have few therapeutic perspectives.

Clinical and Functional Characterization of Novel INSR Variants in Two Families With Severe Insulin Resistance Syndrome.

Objective: Defects in the insulin receptor (INSR) gene cause various severe insulin resistance conditions, including Donohue syndrome (DS), Rabson-Mendenhall syndrome (RMS) and type A insulin resistance (type A-IR). This study aimed to investigate the clinical characterization and molecular defects in three Chinese children with INSR-related insulin resistance syndrome. Methods: We reviewed the clinical data of three Chinese children with INSR-related insulin resistance syndrome from two unrelated kindreds. Genetic analysis was performed using whole-exome sequencing and the effects of the novel variants were further assessed by in vitro functional assays. Results: The proband with type A-IR presented with acanthosis nigricans, hypertrichosis, and euglycemia with mild insulin resistance in early childhood. His sister presented with features typical of type A-IR and was diagnosed with diabetes mellitus with severe insulin resistance at the age of 9.8 years. The proband with DS showed typical dysmorphic characteristics, severe intrauterine growth retardation, extreme insulin resistance, fasting hypoglycemia and postprandial hyperglycemia from birth. The heterozygote variants c.[3670G>A]; c.[3614C>T] were identified in both siblings with type A-IR; and c.[749_751del]; c.[3355C>T] in the patient with DS. In vitro studies showed that the novel variant c.749_751del [p.(Thr250del)] in the α-subunit, reduced expression of the mature INSR protein and severely impaired INSR function. In contrast, the novel variant c.3670G>A [p.(Val1224Met)] in the ß-subunit had no effect on total protein expression and phosphorylation of INSR and Akt, suggesting that the variant p.Val1224Met appeared to be tolerated and was not responsible for the severe insulin resistance. Conclusion: Our study detailed the clinical features of three patients with type A-IR and DS, and identified two novel variants in the INSR gene. Functional assays indicated the novel variant p.Thr250del was pathogenic. In contrast, the novel variant p.Val1224Met was suggested to be tolerated by our experimental data, even though bioinformatics analyses predicted the variant as deleterious.

A novel heterozygous mutation in the insulin receptor gene presenting with type A severe insulin resistance syndrome.

Background Inherited severe insulin resistance syndromes (SIRS) are rare and can be caused by mutations in the insulin receptor gene (INSR). Case presentation A 12-year-old Jamaican girl with a BMI of 24.4 kg/m2 presented with polyuria and polydipsia. A diagnosis of T1DM was made in view of hyperglycaemia (18 mmol/l), and elevated Hba1C (9.9%), and insulin therapy was initiated. Over the next 2 years, she developed hirsutism and acanthosis nigricans, and had minimal insulin requirements with frequent post-prandial hypoglycaemia. In view of this, and her strong family history suggestive of a dominantly inherited type of diabetes, the diagnosis was revisited. Targeted next-generation sequencing (NGS) of the patient's monogenic diabetes genes was performed. What is new? NGS revealed a novel heterozygous missense INSR variant, NM_000208.3:c.3471T>G, p.(His1157Gln), confirming a diagnosis of Type A SIRS. Conclusions Type A SIRS can be difficult to differentially diagnose due to the variable phenotype. Features of insulin resistance may be absent at initial presentation and may develop later during pubertal progress. Awareness of the clinical features and comprehensive genetic testing are essential to identify the condition.

[Analysis of pathogenic gene variant in a patient with neonatal Donohue syndrome].

OBJECTIVE: To explore the genetic basis for a newborn infant suspected with Donohue syndrome. METHODS: Whole exome sequencing (WES) was used to screen potential variants in the child. Suspected variants were validated through Sanger sequencing and real-time PCR. RESULTS: The child was found to carry two heterozygous variants in the INSR gene, including c.3258+4(IVS17)A>G and deletion of exon 2, which were respectively inherited from her mother and father. CONCLUSION: The compound heterozygous variants of the INSR gene probably underlie the disease in this patient.

Clinical characteristics of insulin resistance syndromes: A nationwide survey in Japan.

AIMS/INTRODUCTION: Insulin resistance syndrome (IRS) of type A or B is triggered by gene abnormalities of or autoantibodies to the insulin receptor, respectively. Rabson-Mendenhall/Donohue syndrome is also caused by defects of the insulin receptor gene (INSR), but is more serious than type A IRS. Here, we carried out a nationwide survey of these syndromes in Japan. MATERIALS AND METHODS: We sent questionnaires to a total of 1,957 academic councilors or responsible individuals at certified facilities of the Japan Diabetes Society, as well as at the department pediatrics or neonatology in medical centers with >300 beds. RESULTS: We received 904 responses with information on 23, 30 and 10 cases of type A or B IRS and Rabson-Mendenhall/Donohue syndrome, respectively. Eight cases with type A IRS-like clinical features, but without an abnormality of INSR, were tentatively designated type X IRS, with five of these cases testing positive for PIK3R1 mutations. Fasting serum insulin levels at diagnosis (mean ± standard deviation) were 132.0 ± 112.4, 1122.1 ± 3292.5, 2895.5 ± 3181.5 and 145.0 ± 141.4 µU/mL for type A IRS, type B IRS, Rabson-Mendenhall/Donohue syndrome and type X IRS, respectively. Type A and type X IRS, as well as Rabson-Mendenhall/Donohue syndrome were associated with low birthweight. Type B IRS was diagnosed most frequently in older individuals, and was often associated with concurrent autoimmune conditions and hypoglycemia. CONCLUSIONS: Information yielded by this first nationwide survey should provide epidemiological insight into these rare conditions and inform better healthcare for affected patients.

Mecasermin in Insulin Receptor-Related Severe Insulin Resistance Syndromes: Case Report and Review of the Literature.

Mutations in the insulin receptor (INSR) gene underlie rare severe INSR-related insulin resistance syndromes (SIR), including insulin resistance type A, Rabson⁻Mendenhall syndrome and Donohue syndrome (DS), with DS representing the most severe form of insulin resistance. Treatment of these cases is challenging, with the majority of DS patients dying within the first two years of life. rhIGF-I (mecasermin) has been reported to improve metabolic control and increase lifespan in DS patients. A case report and literature review were completed. We present a case involving a male patient with DS, harbouring a homozygous mutation in the INSR gene (c.591delC). Initial rhIGF-I application via BID (twice daily) injection was unsatisfactory, but continuous subcutaneous rhIGF-I infusion via an insulin pump improved weight development and diabetes control (HbA1c decreased from 10 to 7.6%). However, our patient died at 22 months of age during the course of a respiratory infection in in Libya. Currently available data in the literature comprising more than 30 treated patients worldwide seem to support a trial of rhIGF-I in SIR. rhIGF-I represents a treatment option for challenging SIR cases, but careful consideration of the therapeutic benefits and the burden of the disease is warranted. Continuous application via pump might be advantageous compared to single injections.

Enteroinsular hormones in two siblings with Donohue syndrome and complete leptin deficiency.

The main biochemical hallmark of the rare and lethal condition of Donohue syndrome (DS) is hyperinsulinemia. The roles of the gut and other pancreatic hormones involved in glucose metabolism, satiety and energy expenditure have not been previously reported in DS. Two siblings with genetically confirmed DS and extremely low weight underwent a mixed meal (MM) test where pancreatic hormones insulin, C-peptide, glucagon, active amylin, pancreatic polypeptide (PP) as well as gut hormones active glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), ghrelin, peptide YY (PYY) and leptin were analyzed using a Multiplex assay. Results were compared to those of 2 pediatric controls. As expected, concentrations of insulin, C-peptide and amylin were very high in DS cases. The serum glucagon concentration was undetectable at the time of hypoglycemia. GIPs concentrations were lower in the DS, however, this was not mimicked by the other incretin, GLP-1. Ghrelin concentrations were mainly undetectable (<13.7 pg/mL) in all participants. DS cases had higher PYY and dampened PP concentrations. Leptin levels remained completely undetectable (<137.0 pg/mL). Patients with DS have extremely high amylin levels, completely undetectable serum glucagon and leptin levels with abnormal satiety regulating hormone PP with a relatively normal ghrelin response during a MM test. The low serum GIP might be acting as physiological brake on insulin secretion. The undetectable serum leptin levels suggest the potential of using leptin analogues as therapy for DS patients.

One Novel 2.43Kb Deletion and One Single Nucleotide Mutation of the INSR Gene in a Chinese Neonate with Rabson-Mendenhall Syndrome

Mutations in the insulin receptor (INSR) gene are responsible for Donohue syndrome (DS) and Rabson-Mendenhall syndrome (RMS). Insulin resistance is a feature of both diseases. Our patient was a Chinese neonate suffering from abnormal glucose homeostasis, hyperinsulinemia, dry skin, heavy hair, growth retardation and an elevated testosterone level. To search for candidate point mutations, small insertions or deletions and copy number variants, 2742 inherited disease-gene panel sequencing was performed. One pathogenic mutation (c.3355C>T, p.Arg1119Trp) and a novel 2.43Kb deletion (chr19:7150507-7152938) in INSR were found. The patient was diagnosed as RMS. Sanger sequencing and real-time quantitative polymerase chain reaction (PCR) confirmed the missense variant and microdeletion, respectively. We therefore supposed that these variants were candidate mutations in this case. We report a novel 2.43Kb deletion in INSR gene and provide further proof of the power of next generation sequencing in rare disease diagnosis.

Structural Basis and Genotype-Phenotype Correlations of INSR Mutations Causing Severe Insulin Resistance.

The insulin receptor (INSR) gene was analyzed in four patients with severe insulin resistance, revealing five novel mutations and a deletion that removed exon 2. A patient with Donohue syndrome (DS) had a novel p.V657F mutation in the second fibronectin type III domain (FnIII-2), which contains the α-ß cleavage site and part of the insulin-binding site. The mutant INSR was expressed in Chinese hamster ovary cells, revealing that it reduced insulin proreceptor processing and impaired activation of downstream signaling cascades. Using online databases, we analyzed 82 INSR missense mutations and demonstrated that mutations causing DS were more frequently located in the FnIII domains than those causing the milder type A insulin resistance (P = 0.016). In silico structural analysis revealed that missense mutations predicted to severely impair hydrophobic core formation and stability of the FnIII domains all caused DS, whereas those predicted to produce localized destabilization and to not affect folding of the FnIII domains all caused the less severe Rabson-Mendenhall syndrome. These results suggest the importance of the FnIII domains, provide insight into the molecular mechanism of severe insulin resistance, will aid early diagnosis, and will provide potential novel targets for treating extreme insulin resistance.

Novel heterozygous mutations of the INSR gene in a familial case of Donohue syndrome.

Donohue syndrome (DS), a rare autosomal recessive disease which represents severe insulin resistance, pre- and postnatal growth retardation, hypertrichosis, and dysmorphic features, is caused by mutations in the insulin receptor (INSR) gene. Here, we have reported the clinical, molecular, and biochemical characterizations of a patient with DS. In this article, we have also reported a case with 2 novel INSR mutations and the DS phenotype. Using next-generation sequencing (NGS), we screened 27 known genes involved in inherited maturity-onset diabetes of the young (MODY) and identified compound heterozygous mutations in the INSR gene in the patient with DS, c.62T>G (p.L21R) and c.2563G>T (p.V855F). The positive correlation of these mutations with DS was further validated by Sanger DNA sequencing of his lineal consanguinity, indicating that these pathogenic mutations were inherited maternally and paternally, respectively. Therefore, our finding expanded the number of reported cases of this rare disease and the mutation spectrum of INSR mutation, suggesting that NGS is an accurate, rapid, and cost-effective method for the genetic diagnosis of this rare disease.

A Mutation in INSR in a Child Presenting with Severe Acanthosis Nigricans.

Rabson-Mendenhall syndrome (RMS) is an autosomal recessive disorder due to mutations in the insulin receptor gene (INSR) which is mapped to 19p13.2. RMS is characterized by acanthosis nigricans, generalized lanugo, tooth and nail dysplasia, high nasal bridge, and growth retardation. A 5-year-old female patient was referred due to acanthosis nigricans and generalized lanugo. On her physical examination, severe acanthosis nigricans of the neck, axillae, the external genitalia and antecubital regions, generalized lanugo, mildly decreased subcutaneous fat, dysmorphic facial features, and polydactyly on her left hand were noted. Insulin resistance and impaired glucose tolerance were found. Sequence analysis of the INSR in the patient revealed c.3529+5G>A mutation in homozygous state. RMS should be suspected in a patient with characteristic physical features and insulin resistance.

Molecular mechanisms of insulin resistance in 2 cases of primary insulin receptor defect-associated diseases.

BACKGROUND: Defects of the insulin receptor gene ( INSR ) cause wide spectra of congenital insulin resistance. Monoallelic defects result in milder insulin-resistant diabetes mellitus with acanthosis nigricans (IRAN, type A). Whereas, leprechaunism (Donahue syndrome), the most severe condition with lethality during the infantile period is caused by biallelic defects of INSR . MATERIALS AND METHODS: We detected 2 missense mutations in 2 cases of leprechaunism and IRAN, type A, and reduced mRNA expression in the leprechaunism case. We performed an in vitro analysis to confirm that the 2 missense mutations are causative. RESULTS: The heterozygote mutations c.3436G>A (p.Gly1146Arg) and c.294C>A (p.Ser98Arg) were identified in a male patient with IRAN, type A and a female patient with leprechaunism, respectively. Gly1146Arg was previously reported in a diabetic case without precise functional analyses, and Ser98Arg is a novel mutation. Gly1146 and Ser98 are located on the tyrosine kinase domain and ligand-binding domain of INSR, respectively, and in vitro analyses (assay for insulin binding and phosphorylation) revealed that each mutation disrupted protein functions and properties. In the leprechaunism case, mutations in INSR other than Ser98Arg were not identified, and qRT-PCR analysis revealed that mRNA expression of INSR in lymphocytes was reduced in the leprechaunism case. CONCLUSION: Our study indicates that the 2 missense mutations of INSR , Gly1146Arg, and Ser98Arg, are responsible for insulin resistance, and, suggests that mutations not contained within INSR , but leading to decreased INSR expression should be considered for the patients who show insulin resistance without any mutations in the coding sequence of INSR.

Identification of a Novel Homozygous INSR Variant in a Patient with Rabson-Mendenhall Syndrome from the United Arab Emirates.

BACKGROUND/AIMS: This study aimed to identify, clinically and molecularly, the causality of Rabson-Mendenhall syndrome in an Emirati family. It is one of the monogenic syndromes of abnormal glucose homeostasis, which result from insulin receptor defects. METHODS: A novel nonsynonymous variant in the INSR gene was uncovered by whole exome sequencing and confirmed using Sanger sequencing in the patient and his parents. Various in silico tools were utilized to analyze the functional consequences of the variant. RESULTS: Results revealed a previously unreported INSR variant in the family: c.421C>T (p.Arg141Trp). Homozygosity for the variant was found in the patient, while both parents were heterozygous. CONCLUSION: The nonsynonymous protein change hit a highly conserved arginine residue in the insulin-binding α-subunit of the receptor and was deemed 'functionally damaging' by a myriad of bioinformatics tools. This report is a step forward along the way of achieving a better molecular and clinical characterization of Rabson-Mendenhall syndrome.