A syndrome of insulin resistance resembling leprechaunism in five sibs of consanguineous parents

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 in an Egyptian infant: a case report

Objectives

We aim to report a case of Donohue syndrome (DS) which is a rare genetically encoded, autosomal inherited recessive disorder linked with severe insulin-resistant diabetes.

Case presentation

We hereby report a case of a 4 month -old girl infant with DS. The patient exhibited dysmorphic facial features, severe growth retardation, fasting hypoglycemia, postprandial hyperglycemia, and hyperinsulinemia which are the hallmarks of DS. The diagnosis of DS was confirmed by genetic analysis. The patient was treated with high-dose insulin and frequent nasogastric formula milk feeding to achieve reasonable glycemic control.

Conclusions

We reported a typical case of DS in a 4-month-old female infant characterized by peculiar dysmorphic features and failure to thrive. She also fulfilled the biochemical criteria of fasting hypoglycemia, postprandial hyperglycemia, and severe hyperinsulinemia. The diagnosis was confirmed by a molecular genetic study. Our patient achieved reasonable glycemic control after treatment with high-dose insulin.

Monogenic diabetes: a gateway to precision medicine in diabetes

Monogenic diabetes refers to diabetes mellitus (DM) caused by a mutation in a single gene and accounts for approximately 1%-5% of diabetes. Correct diagnosis is clinically critical for certain types of monogenic diabetes, since the appropriate treatment is determined by the etiology of the disease (e.g., oral sulfonylurea treatment of HNF1A/HNF4A-diabetes vs. insulin injections in type 1 diabetes). However, achieving a correct diagnosis requires genetic testing, and the overlapping of the clinical features of monogenic diabetes with those of type 1 and type 2 diabetes has frequently led to misdiagnosis. Improvements in sequencing technology are increasing opportunities to diagnose monogenic diabetes, but challenges remain. In this Review, we describe the types of monogenic diabetes, including common and uncommon types of maturity-onset diabetes of the young, multiple causes of neonatal DM, and syndromic diabetes such as Wolfram syndrome and lipodystrophy. We also review methods of prioritizing patients undergoing genetic testing, and highlight existing challenges facing sequence data interpretation that can be addressed by forming collaborations of expertise and by pooling cases.

Leucine Rich Repeat Proteins: Sequences, Mutations, Structures and Diseases

Mutations in the genes encoding Leucine Rich Repeat (LRR) containing proteins are associated with over sixty human diseases; these include high myopia, mitochondrial encephalomyopathy, and Crohn's disease. These mutations occur frequently within the LRR domains and within the regions that shield the hydrophobic core of the LRR domain. The amino acid sequences of fifty-five LRR proteins have been published. They include Nod-Like Receptors (NLRs) such as NLRP1, NLRP3, NLRP14, and Nod-2, Small Leucine Rich Repeat Proteoglycans (SLRPs) such as keratocan, lumican, fibromodulin, PRELP, biglycan, and nyctalopin, and F-box/LRR-repeat proteins such as FBXL2, FBXL4, and FBXL12. For example, 363 missense mutations have been identified. Replacement of arginine, proline, or cysteine by another amino acid, or the reverse, is frequently observed. The diverse effects of the mutations are discussed based on the known structures of LRR proteins. These mutations influence protein folding, aggregation, oligomerization, stability, protein-ligand interactions, disulfide bond formation, and glycosylation. Most of the mutations cause loss of function and a few, gain of function.

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-β 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.

Classic Case Report of Donohue Syndrome (Leprechaunism; OMIM *246200): The Impact of Consanguineous Mating

Donohue syndrome ([DS]; leprechaunism) describes a genetic autosomal recessive disorder that results from the presence of homozygous or compound heterozygous mutations in the insulin receptor gene (INSR; 19p13.3-p13.2).Donohue syndrome is associated with a fatal congenital form of dwarfism with features of intrauterine and postnatal growth retardation, exaggerated hyperglycemia with hyperinsulinism and dysmorphic abnormalities.We present a case of DS owing to the rarity of this syndrome (1 case in every million births). We discuss how the disease presents, its genetic underpinning, and its prevention.The case was encountered in an Arab male born on 1 September, 2014, for consanguineous parents. The delivery was via cesarean section at 37 weeks gestation due to severe intrauterine growth restriction and nonprogress labor term. The patient was admitted to the Neonatal Intensive Care Unit due to infection, and jaundice. Dysmorphic features, abnormalities of the craniofacial region, low birth weight, skin abnormalities, abdominal distension and hypertrichosis were observed. Laboratory examinations showed, hyperinsulinism, increased C-peptide, thrombocytopenia, leucopenia, and anemia.The diagnosis of DS was done based on the combinations of typical dysmorphic characteristics, clinical evaluation, supported by genetic analysis and exaggerated biochemical results. Genetic diagnosis of DS was performed through analysis of DNA via polymerase chain reaction (PCR). A qualitative real-time PCR was used, to monitor the amplification of a targeted DNA molecule during the PCR. Other technique using sequencing of the INSR gene, which permits genetic diagnosis, counseling, and antenatal diagnoses in subsequent pregnancies, were also performed.Treatment of DS is supportive and requires the combined efforts of a multidisciplinary team, which include pediatricians, endocrinologists, dermatologists, and other health care professionals. Currently, treatment with recombinant insulin-like growth factor 1 demonstrates effectiveness, and a combination treatment with insulin-like growth factor binding protein 3 resulted in an increased lifespan.There is a scarcity of genetic information on DS among the Arab population. Consanguinity is one of underlying reasons for the appearance of rare genetic disorders. Inbreeding has long been considered a controversial phenomenon. Genetic counseling and overwhelming the alertness of the negative consequences of consanguinity on public health are warranted.

Severe insulin resistance alters metabolism in mesenchymal progenitor cells

Donohue syndrome (DS) is characterized by severe insulin resistance due to mutations in the insulin receptor (INSR) gene. To identify molecular defects contributing to metabolic dysregulation in DS in the undifferentiated state, we generated mesenchymal progenitor cells (MPCs) from induced pluripotent stem cells derived from a 4-week-old female with DS and a healthy newborn male (control). INSR mRNA and protein were significantly reduced in DS MPC (for β-subunit, 64% and 89% reduction, respectively, P < .05), but IGF1R mRNA and protein did not differ vs control. Insulin-stimulated phosphorylation of INSR or the downstream substrates insulin receptor substrate 1 and protein kinase B did not differ, but ERK phosphorylation tended to be reduced in DS (32% decrease, P = .07). By contrast, IGF-1 and insulin-stimulated insulin-like growth factor 1 (IGF-1) receptor phosphorylation were increased in DS (IGF-1, 8.5- vs 4.5-fold increase; INS, 11- vs 6-fold; P < .05). DS MPC tended to have higher oxygen consumption in both the basal state (87% higher, P =.09) and in response to the uncoupler carbonyl cyanide-p-triflouromethoxyphenylhydrazone (2-fold increase, P =.06). Although mitochondrial DNA or mass did not differ, oxidative phosphorylation protein complexes III and V were increased in DS (by 37% and 6%, respectively; P < .05). Extracellular acidification also tended to increase in DS (91% increase, P = .07), with parallel significant increases in lactate secretion (34% higher at 4 h, P < .05). In summary, DS MPC maintain signaling downstream of the INSR, suggesting that IGF-1R signaling may partly compensate for INSR mutations. However, alterations in receptor expression and pathway-specific defects in insulin signaling, even in undifferentiated cells, can alter cellular oxidative metabolism, potentially via transcriptional mechanisms.

Two novel mutations identified in familial cases with Donohue syndrome

Donohue syndrome (DS) is a rare and lethal autosomal recessive disease caused by mutations in the insulin receptor (INSR) gene, manifesting marked insulin resistance, severe growth retardation, hypertrichosis, and characteristic dysmorphic features. We report the clinical, molecular, and biochemical characterization of three new patients with DS, and address genotype–phenotype issues playing a role in the pathophysiology of DS. A female infant born to first-degree cousins Muslim Arab parents and two brothers born to first-degree cousins Druze parents presented classical features of DS with hypertrophic cardiomyopathy and died in infancy. Each patient was found homozygous for one missense mutation within the extracellular domain of the INSR gene. Western blot analysis identified the proreceptor of INSR, but not its mature subunits alpha and beta. Of 95 healthy Muslims, no heterozygous was found and of 52 healthy Druze from the same village, one was heterozygous. This study presents two novel familial mutations in the alpha subunit of the INSR which appear to impair post-translational processing of the INSR, resulting loss of its function. Both mutations cause DS with hypertrophic cardiomyopathy and early death. Identification of the causative mutation enables prevention of this devastating disease.

Metreleptin improves blood glucose in patients with insulin receptor mutations

CONTEXT

Rabson-Mendenhall syndrome (RMS) is caused by mutations of the insulin receptor and results in extreme insulin resistance and dysglycemia. Hyperglycemia in RMS is very difficult to treat, and patients are at risk for early morbidity and mortality from complications of diabetes.

OBJECTIVE

Our objective was to study 1-year effects of recombinant human methionyl leptin (metreleptin) in 5 patients with RMS and 10-year effects in 2 of these patients.

DESIGN AND SETTING

We conducted an open-label nonrandomized study at the National Institutes of Health.

PATIENTS

Patients were adolescents with RMS and poorly controlled diabetes.

INTERVENTION

Two patients were treated with escalating doses (0.02 up to 0.22 mg/kg/d) of metreleptin for 10 years, including 3 cycles of metreleptin withdrawal and reinitiation. In all 5 patients, 1-year effects of metreleptin (0.22 mg/kg/d) were studied.

OUTCOME MEASURES

Hemoglobin A1c (HbA1c) and body mass index (BMI) z-scores were evaluated every 6 months.

RESULTS

HbA1c decreased from 11.4% ± 1.1% at baseline to 9.3% ± 1.9% after 6 months and 9.7% ± 1.6% after 12 months of metreleptin (P = .007). In patients treated for 10 years, HbA1c declined with each cycle of metreleptin and rose with each withdrawal. BMI z-scores declined from -1.4 ± 1.8 at baseline, to -2.6 ± 1.6 after 12 months of metreleptin (P = .0006). Changes in BMI z-score correlated with changes in HbA1c (P < .0001).

CONCLUSIONS

Metreleptin treatment for 12 months was associated with a 1.7% reduction in HbA1c; part of this improvement was likely mediated via decreased BMI. Metreleptin is a promising treatment option for RMS, but additional therapies are needed to achieve HbA1c targets.

A novel leprechaunism mutation, Cys807Arg, in an Arab infant: a rare cause of hypoglycaemia

Leprechaunism is a rare autosomal recessive disorder which is usually fatal in early infancy or childhood. There is a paucity of genetic data on leprechaunism in the Arab population. A 4-month-old boy presented with jaundice, asymptomatic hypoglycaemia and growth retardation with features of leprechaunism. A novel Cys807Arg was identified, which could facilitate antenatal diagnosis for families in the Middle East.

Molecular characterization of a novel p.R118C mutation in the insulin receptor gene from patients with severe insulin resistance

CONTEXT

Mutations of the insulin receptor gene (INSR) can cause genetic syndromes associated with severe insulin resistance.

OBJECTIVES

We aimed to analyse INSR mutations in Saudi patients with severe insulin resistance.

DESIGN

Ten patients with Type A insulin resistance syndrome from five unrelated Saudi families were investigated. The entire coding region of INSR was sequenced. The founder effect was assessed by microsatellite haplotype analysis. The functional effect of the mutation was investigated by in vitro functional assays.

RESULTS

A novel biallelic c.433 C>T (p.R118C) mutation was detected in all patients. The c.433 C>T (p.R118C) sequence variation was not found in 100 population controls. The arginine residue at position 118 is located in the ligand-binding domain of INSR and is highly conserved across species. Microsatellite haplotype analysis of these patients indicated that p.R118C was a founder mutation created approximately 2900 years ago. The wild-type and mutant (R118C) INSR were cloned and expressed in CHO cells for functional analysis. Specific insulin binding to the mutant receptor was reduced by 83% as compared to wild-type (WT), although the mutant receptor was processed and expressed on the cell surface. Insulin-mediated receptor autophosphorylation was also significantly reduced in CHO(R118C) cells.

CONCLUSIONS

Biallelic c.433 C>T (p.R118C) mutation of INSR causes significant damage to insulin binding and insulin-mediated signal transduction. p.R118C is a founder mutation frequently present in the Saudi patients with severe insulin resistance.

Founder effect in the Horn of Africa for an insulin receptor mutation that may impair receptor recycling

AIMS/HYPOTHESIS

Genetic insulin receptoropathies are a rare cause of severe insulin resistance. We identified the Ile119Met missense mutation in the insulin receptor INSR gene, previously reported in a Yemeni kindred, in four unrelated patients with Somali ancestry. We aimed to investigate a possible genetic founder effect, and to study the mechanism of loss of function of the mutant receptor.

METHODS

Biochemical profiling and DNA haplotype analysis of affected patients were performed. Insulin receptor expression in lymphoblastoid cells from a homozygous p.Ile119Met INSR patient, and in cells heterologously expressing the mutant receptor, was examined. Insulin binding, insulin-stimulated receptor autophosphorylation, and cooperativity and pH dependency of insulin dissociation were also assessed.

RESULTS

All patients had biochemical profiles pathognomonic of insulin receptoropathy, while haplotype analysis revealed the putative shared region around the INSR mutant to be no larger than 28 kb. An increased insulin proreceptor to β subunit ratio was seen in patient-derived cells. Steady state insulin binding and insulin-stimulated autophosphorylation of the mutant receptor was normal; however it exhibited decreased insulin dissociation rates with preserved cooperativity, a difference accentuated at low pH.

CONCLUSIONS/INTERPRETATION

The p.Ile119Met INSR appears to have arisen around the Horn of Africa, and should be sought first in severely insulin resistant patients with ancestry from this region. Despite collectively compelling genetic, clinical and biochemical evidence for its pathogenicity, loss of function in conventional in vitro assays is subtle, suggesting mildly impaired receptor recycling only.

Mutations of a country: a mutation review of single gene disorders in the United Arab Emirates (UAE)

The United Arab Emirates inhabitants are ethnically diverse, with ancestries from Arabia, Persia, Baluchistan, and Africa. However, the majority of the current five million inhabitants are expatriates from the Asian subcontinent, Middle Eastern, African, and European countries. Consanguineous marriages within most UAE subpopulations are still the norm, leading to the formation of isolates and higher frequencies of recessive conditions. The UAE is ranked sixth in terms of prevalence of birth defects, with more than 270 genetic disorders reported in the national population. The UAE has high frequencies of blood disorders including thalassemias, sickle cell disease, and G6PD. In addition, certain genetic conditions are relatively common including cystic fibrosis, Joubert, and Meckel syndromes. Furthermore, numerous rare congenital malformations and metabolic disorders have been reported. We review the single gene disorders that have been studied at the molecular level in the UAE (which currently stand at 76) and compile the mutations found. Several novel (p.S2439fs) mutations have been reported including c.7317delA in NF1, c.5C>T (p.A2V) in DKC1, c.1766T>A (p.I589N) in TP63, and c.2117G>T (p.R706L) in VLDLR. We hope that this review will form the basis to establish a UAE mutations database and serve as a model for the collection of mutations of a country.

Insulin Receptor and its Relationship with Different Forms of Insulin Resistance

Insulin plays an important role in maintaining the whole organism’s homeostasis. The presence of insulin receptors in all vertebrates and invertebrates cells reflects the diversity of regulatory processes in which this hormone is involved. Furthermore, many different factors may influence the level of insulin receptor expression. These factors include e.g. the sole insulin or stage of development. Mutations in the receptor may lead to the development of insulin resistance. These mutations differ in the level of severity and are frequently associated with diabetes mellitus, hypertension, cardiovascular disorders, heart failure, metabolic syndrome and infertility in women. More than 50 mutations in insulin receptor gene have already been characterized. These mutations are associated with rare forms of insulin resistance like leprechaunism, insulin resistance type A or Rabson-Mendenhall syndrome. Molecular analysis of insulin receptor gene may lead to a better understanding of molecular mechanisms underlying various types of insulin resistance and help to develop more efficient treatment.

Rabson-Mendenhall syndrome: medullary sponge kidney, a new component

Rabson-Mendenhall syndrome is a rare genetic disorder characterized by severe insulin resistance, extreme hyperinsulinemia, postprandial hyperglycemia, growth retardation, and dysmorphisms. Enlargement of the kidneys and nephrocalcinosis have been described previously. We report a 10-year-old boy who presented with gross hematuria, unilateral hydronephrosis, and the initial diagnosis of bilateral extensive medullary nephrocalcinosis. Medullary sponge kidney (MSK) was included in the differential diagnosis given the ultrasound findings. Further evaluation by intravenous pyelogram confirmed the suspected bilateral MSK. Given the patient's history of hydronephrosis due to an obstructing renal stone and MSK, urine calcium excretion was assessed and found to be markedly increased at 9.5 mg/kg per day. To our knowledge, this is the first report of Rabson-Mendenhall syndrome and an association with MSK. We recommend evaluation for nephrocalcinosis, MSK, and hypercalciuria in all children diagnosed with Rabson-Mendenhall syndrome.

Clinical evidence that hyperinsulinaemia independent of gonadotropins stimulates ovarian growth

OBJECTIVE

Ovarian enlargement is a constant feature of syndromes of extreme insulin resistance. The objective of this study is to show the role of insulin on ovarian growth in the presence of low gonadotropin levels.

PATIENTS

Seven young patients with syndromes of extreme insulin resistance (five with lipodystrophy, one with Type B syndrome and one with Rabson-Mendenhall syndrome) were studied.

MEASUREMENTS

Baseline LH concentrations and luteinizing hormone releasing hormone (LHRH) tests were performed. Total testosterone, insulin and C-peptide values were measured. Pelvic ultrasounds were performed.

RESULTS

Four patients were prepubertal (age range 7-10 years old) and had prepubertal gonadotropin levels, and 2 of the 4 who were tested did not respond to LHRH (NIH 10 and RM-PAL). Three patients were Tanner stage 4 (age range 13-17 years old) and had low gonadotropins that did not respond to LHRH stimulation test. All seven patients had marked hyperinsulinaemia and 6 of 7 had at least one enlarged ovary. Testosterone values were increased in 4 of 7 patients.

CONCLUSION

This represents the first example of the pathologic role of insulin to stimulate ovarian growth with low circulating gonadotropins. Thus, while ovarian growth and steroidogenesis are normally stimulated by gonadotropins at puberty, hyperinsulinaemia stimulates pathologic growth of the ovary and an androgenic steroid profile that is active at all ages. We suggest that these patients constitute a model to separate the effect of insulin from gonadotropin in stimulating ovarian growth and/or steroidogenesis.

Clinical course of genetic diseases of the insulin receptor (type A and Rabson-Mendenhall syndromes): a 30-year prospective

The interaction of insulin with its cell surface receptor is the first step in insulin action and the first identified target of insulin resistance. The insulin resistance in several syndromic forms of extreme insulin resistance has been shown to be caused by mutations in the receptor gene. We studied 8 female patients with the type A form of extreme insulin resistance and 3 patients (2 male and 1 female) with the Rabson-Mendenhall syndrome and followed the natural history of these patients for up to 30 years. The 11 patients ranged in age from 7 to 32 years at presentation. All 11 patients had extreme insulin resistance, acanthosis nigricans, and hyperandrogenism in the female patients, and all but 1 were of normal body weight. This phenotype strongly predicts mutations in the insulin receptor: of the 8 patients studied, 7 were found to have mutations. Similar results from the literature are found in other patients with type A and Rabson-Mendenhall syndromes and leprechaunism. The hyperandrogenic state resulting from hyperinsulinemia and insulin resistance in these patients was extreme: 6 of 8 patients had ovarian surgery to correct the polycystic ovarian syndrome and elevation of serum testosterone. By contrast, a larger group of insulin-resistant patients who were obese with hyperandrogenism, insulin resistance, and acanthosis nigricans (HAIR-AN syndrome) did not have a high probability of mutations in the insulin receptor. The morbidity and mortality of these patients were high: 3 of 11 died, 9 of 11 were diabetic and 1 had impaired glucose tolerance, and 7 of 9 patients had 1 or more severe complication of diabetes. Our literature review revealed that the mortality of leprechaunism is so high that the term leprechaunism should be restricted to infants or young children under 2 years of age. Analogous to patients with the common forms of type 2 diabetes, these patients had a heterogeneous course. In 2 patients who were able to maintain extremely high endogenous insulin production, the fasting blood glucose remained normal even though post-glucose-challenge levels were elevated. Most patients, however, required large doses of exogenous insulin to ameliorate the severe hyperglycemia. Preliminary results of a recent study suggest that recombinant leptin administration may benefit these patients with severe insulin resistance.

Ocular manifestations of Donohue's syndrome

INTRODUCTION

Donohue's syndrome, also known as Leprechaunism, is a rare autosomal recessive disease that manifests at birth with symptoms of endocrine dysfunction. Metabolic characteristics of the disease include postprandial hyperglycemia, fasting hypoglycemia, insulin resistance, hyperinsulinemia, and failure to thrive. The physical features most often associated with this condition include hypertrichosis, pachyderma, acanthosis nigricans, prominent genitalia, and elfin-like facial characteristics of prominent eyes, wide nostrils, thick lips, and large, low-set ears. Not only is this syndrome rare, but it often results in infant and early childhood mortality. The literature regarding ocular manifestations is limited.

CASE REPORT

We present a case of a 29-year-old male with Donohue's syndrome and significant ocular findings including a subluxated mature cataract, retinal detachment, high myopia, and optic atrophy.

DISCUSSION

These ocular sequelae are discussed with regard to the noted endocrine dysfunction and its effects on tissue development and growth.

Familial acanthosis nigricans with madarosis

We report familial acanthosis nigricans affecting a 35-year-old woman, her 7-year-old son and 5-year-old daughter. Absence of the eyebrows and eyelashes was noted in this family. The mother had no axillary hair and her pubic hair was sparse. The boy also suffered from congenital heart disease and a congenital cataract in the left eye. The combination of acanthosis nigricans and ectodermal defects in this family may represent a distinct nosological entity.

Homozygosity for a new mutation (Ile119-->Met) in the insulin receptor gene in five sibs with familial insulin resistance

Mutations in the insulin receptor gene can cause genetic syndromes such as leprechaunism that are associated with extreme insulin resistance. We have investigated a patient with leprechaunism born of a consanguineous marriage. All 22 exons of the insulin receptor gene were screened for mutations using denaturing gradient gel electrophoresis. Thereafter, the nucleotide sequences of selected exons were determined directly. The patient was homozygous for a point mutation in exon 2 of the insulin receptor gene which results in the substitution of methionine for isoleucine at codon 119. Thus, the mutant allele encodes a receptor that has a mutation in the putative insulin binding domain. Accordingly, the mutant receptor would be predicted not to transduce the insulin signal effectively. In spite of a homozygous abnormality of the insulin receptor gene and many of the clinical features of severe insulin resistance, the proband's clinical syndrome was noticeably different from previously described patients with leprechaunism who usually die within the first six months of life. There are a total of nine children in the family, five of whom are homozygous for the Ile119-->Met mutation in the insulin receptor gene, and are clinically affected with varying degrees of severity. Four unaffected sibs are clinically normal; two are heterozygous carriers of the mutant allele, one is homozygous for the normal allele, and one unaffected sib was not available for molecular studies.

Acanthosis nigricans

Acanthosis nigricans is a mucocutaneous eruption that occurs in a strikingly exuberant form as a marker for a highly malignant and rapidly fatal internal cancer. Recently, it has been recognized that acanthosis nigricans may also be a relatively common marker for increased long-term risk of the less dramatic but potentially serious systemic disorders associated with insulin resistance and compensatory increased insulin secretion.