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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.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.We conducted an open-label nonrandomized study at the National Institutes of Health.Patients were adolescents with RMS and poorly controlled diabetes.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.Hemoglobin A1c (HbA1c) and body mass index (BMI) z-scores were evaluated every 6 months.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).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.

Humans with congenital absence of the islets of Langerhans and mice rendered null for the insulin receptor rapidly develop severe hyperglycemia and ketoacidosis and, if untreated, die in the early neonatal period. In contrast, children with homozygous or compound heterozygous mutations of the insulin receptor gene, although hyperglycemic postprandially, survive for many months without developing ketoacidosis. Paradoxically, they often develop hypoglycemia. The rarity of the condition and the difficulties of undertaking metabolic studies in ill infants have limited the physiological information that might explain the clinical features. We studied a boy with Donohue's syndrome who represents a further example of the null phenotype, with two different and novel nonsense mutations in the alpha-subunit of the receptor. He survived for 8 months without developing ketoacidosis, and fasting hypoglycemia was a frequent problem. Despite the complete absence of insulin receptors, evidence for persistent insulin-like effects on fat and liver was seen; fasting plasma beta-hydroxybutyrate and nonesterified fatty acid levels were low, fell further during the early postprandial period, and failed to rise in response to hypoglycemia. The inverse relationships between plasma insulin and insulin-like growth factor-binding protein-1 levels were maintained, suggesting persistent hepatic effects of insulin. GH levels measured over a 6.5-h period were low throughout. Thus, the differences between congenital insulin deficiency vs. insulin receptor deficiency in humans may be explained by persistent insulinomimetic activity of the grossly elevated plasma insulin presumably being mediated through the type 1 insulin-like growth factor receptor. As GH plays a critical role in the regulation of ketogenesis during insulinopenia in humans, but not in rodents, this may contribute to the distinct phenotype of human vs. mouse insulin receptor knockouts.

Mutations in the insulin receptor gene cause the severe insulin-resistant syndromes leprechaunism and Rabson-Mendenhall syndrome, whose metabolic features include fasting hypoglycemia, postprandial hyperglycemia, and extremely elevated insulin levels. Patients with Rabson-Mendenhall syndrome have a protracted course and eventually develop ketoacidosis. To determine the mechanism causing this progression and the paradoxical fasting hypoglycemia, we conducted a retrospective study in a patient with Rabson-Mendenhall syndrome, who was a compound heterozygous for two missense mutations affecting the kinase domain of the insulin receptor β-subunit (I1115T and R1131W). At birth, the patient had fasting hypoglycemia and postprandial hyperglycemia. This was followed at approximately 3 yr of age by constant hyperglycemia and, at 6 yr of age, by constant ketoacidosis. Urinary organic acids during ketoacidosis resembled those of patients with type 1 diabetes. Plasma glucose levels increased (r2 = 0.31; P < 0.01), wh...

Leprechaunism is an autosomal recessive disorder caused by mutations in the insulin receptor gene and characterized by intrauterine and postnatal growth restriction, abnormal glucose homeostasis, and severe insulin-resistance. Here we report the biochemical and molecular characterization of a male patient, NZ, who died at 2 yr of age with this syndrome. 125I-Insulin binding to fibroblasts from the proband, his mother, father, and unaffected sister was reduced to 8, 53, 38, and 35% of controls, respectively. Analysis of the insulin receptor gene by polymerase chain reaction amplification using primers flanking each of the 22 exons and direct DNA sequencing identified 2 different mutations in the proband. The paternal mutation was an in-frame deletion of base pairs 1159-1161 in exon 3, which resulted in the loss of the codon for Asn-281. The maternal mutation was a G-->A transition in the first nucleotide of the splice-donor junction in intron 13. The maternal mutation activated a cryptic splice site 27 base pairs upstream in exon 13 and caused an in-frame deletion of amino acids 859-867 of the extracellular domain of the insulin receptor beta subunit. Identification of both mutations enabled prenatal diagnosis in 2 subsequent pregnancies. In the first pregnancy, DNA from cells cultured from chorionic villus (CV) biopsies carried both mutations in the insulin receptor gene. In the second pregnancy, DNA from the CV biopsy cells was negative for both mutations, indicating that the fetus was unaffected by leprechaunism. Insulin binding could not be used in prenatal diagnosis because cells cultured from some control CV biopsies failed to bind insulin. These data indicate that patient NZ with leprechaunism was a compound heterozygote for 2 novel mutations in the insulin receptor gene and that direct DNA sequencing enables prenatal diagnosis for this lethal disorder.

Mutations in the insulin receptor gene may lead to insulin resistance and diabetes mellitus in some patients. We have studied an insulin-resistant patient with leprechaunism. Insulin binding to the patient's fibroblasts was markedly decreased. Determination of the nucleotide sequence of the patient's insulin receptor gene revealed heterozygosity for a 2-basepair deletion in exon 15. If the premessenger ribonucleic acid (pre-mRNA) is spliced normally, it causes a replacement of codon 970 in the beta-subunit with a premature chain termination codon, thereby deleting most of the intracellular domain of the receptor. The mRNA transcribed from the allele with a 2-base-pair deletion is likely to be unstable because mRNA transcripts from this allele could not be detected by complementary DNA sequencing. Northern blot analysis showed that the patient's insulin receptor mRNA was decreased by 90% compared with that of a control subject, thus suggesting that the patient is a compound heterozygote for two mutations that decrease levels of insulin receptor mRNA. This deletion mutation in exon 15 seems to be a de novo mutation, because it was not detected in either parent. Investigation of the inheritance of a silent sequence polymorphism in exon 17 provided that the deletion occurred in the maternal allele. Furthermore, linkage analysis suggests that the second mutation is derived from the patient's father, although we could not directly identify it by sequencing the coding region of the insulin receptor gene. Therefore, it is possible that this mutation is present in a regulatory domain of the insulin receptor gene, acting in cis-dominant fashion to reduce the levels of insulin receptor mRNA. Analyses of the hypervariable region in the myoglobin and pMCT118 loci were consistent with the assumption that the father and mother studied here are indeed the biological parents of the diseased patient. We hereby conclude that the patient is a compound heterozygote for two mutant alleles, both of which are responsible for the reduced levels of insulin receptor mRNA and insulin binding.

We have identified a novel mutation of the human insulin receptor gene in a previously unreported patient with leprechaunism, leprechaun Rochester. This mutation consists of deletion of three nucleotides (GAA) in exon 2 and results in loss of the lysine-121 in the putative ligand-binding domain of the alpha-subunit. To analyze this mutation, we prepared a corresponding mutant insulin receptor by site-directed mutagenesis and expressed the receptor in Chinese hamster ovary cells. Although the mutant receptor displayed normal insulin binding, abnormalities were found in autophosphorylation and in phosphorylation of endogenous and exogenous protein substrates. These abnormalities consisted of increased basal kinase activity, but blunted insulin-stimulated responsiveness. Importantly, cells that expressed the mutant receptor showed markedly decreased insulin- and serum-stimulated DNA synthesis compared to untransfected control cells and cells transfected with the wild-type insulin receptor. These findings suggest that deletion of lysine-121 in conjunction with a presumed, but thus far unidentified, second mutant allele contributed significantly to the lethal insulin-resistant state in this patient with leprechaunism.

Mutations in the insulin receptor gene cause the severe insulin-resistant syndromes leprechaunism and Rabson-Mendenhall syndrome. There is no accepted therapy for these inherited conditions. Here we report the results of recombinant human GH (rhGH) and recombinant human insulin-like growth factor-I (rhIGF-I) treatment of a male patient, Atl-2, with Rabson-Mendenhall syndrome. The patient was small for gestational age, had premature dentition, absence of sc fat, acanthosis nigricans, fasting hypoglycemia and postprandial hyperglycemia, and extremely high concentrations of circulating insulin (up to 8500 microU/mL). Fibroblasts and lymphoblasts established from this patient had reduced insulin binding, which was 20-30% of the control value. Binding of epidermal growth factor, IGF-I, and GH to the patient's fibroblasts was normal. The growth of fibroblasts cultured from patient Atl-2 in vitro was intermediate between that of fibroblasts from patients with leprechaunism and control values. The patient's growth curve in vivo was far below the fifth percentile despite adequate nutrition. To stimulate growth, therapy with rhGH was initiated, the rationale being to stimulate hepatic IGF-I production and IGF-I receptor signaling, and bypass the inherited block in insulin receptor signaling. Therapy with rhGH (up to 0.5 mg/kg.week) did not improve growth and failed to increase the levels of circulating IGF-I and IGF-binding protein-3 over a 14-month period. As rhGH could not stimulate growth, rhIGF-I (up to 100 micrograms/kg.day) was given by daily sc injection. No increase in growth velocity was observed over a 14-month period. These results indicate that both GH and IGF-I fail to correct growth in a patient with severe inherited insulin resistance. The lack of efficacy of IGF-I treatment may be related to multiple factors, such as the poor metabolic state of the patient, the deficiency of serum carrier protein for IGF-I, an increased clearance of the growth factor, IGF-I resistance in target cells at a receptor or postreceptor level, or an inhibitory action of the mutant insulin receptors on IGF-I receptor signaling.

[125I]Insulin binding has been studied in two patients with extreme insulin resistance using cultured B-lymphocytes transformed with Epstein-Barr virus. A cell line from a female infant with leprechaunism had insulin binding which was decreased 90% below the lower limit of normal. Lymphocytes from a young woman with type A extreme insulin resistance (associated with acanthosis nigricans and virilization) had insulin binding which was 80% depressed. In both cases, the defect in binding resulted from a decrease in the number of receptors per cell. The remaining receptors had normal properties, including a normal affinity for insulin and a normal specificity for insulin analogs. Insulin binding in cultured lymphocytes from these two insulin-resistant patients was also inhibited normally by antibodies to the insulin receptor. Immunological assays using anti-receptor antibodies confirmed the conclusion that the number of receptors was decreased. Affinity labeling of the leprechaun insulin receptor with [125I]insulin demonstrated the existence of an alpha-subunit with apparently normal molecular weight (130,000 daltons). However, the number of receptor molecules per cell appeared reduced.

Insulin stimulation of glycogen synthase and of thymidine incorporation into DNA has been examined in fibroblasts derived from three insulin-resistant patients: two with the type A syndrome of insulin resistance and acanthosis nigricans and one with the syndrome of leprechaunism. All three cell lines were previously shown to exhibit abnormal insulin-binding properties with alterations in receptor number or affinity. In the basal state, fibroblasts from all three patients contained normal levels of total glycogen synthase activity. Two of the cell lines, those of type A patient A-l and those of the leprechaun infant, had an abnormally high percentage of the enzyme in its glucose-6-phosphate-independent or dephosphorylated form and lower than normal cellular glycogen stores, consistent with an inverse correlation between percent I activity and glycogen content observed with other cells. Cells from patient A-3 had normal levels of glycogen and a low percentage of enzyme in the independent form. Insulin activ...

Insulin binding has been characterized on fibroblasts cultured from two patients with the type A syndrome of insulin resistance and acanthosis nigricans (A-l and A-3) and from one infant with insulin resistance associated with leprechaunism. [125I]Insulin binding was markedly decreased in cells from all three patients. The defect in insulin receptors appeared specific; binding of insulin-like growth factor I was normal. Assuming a cooperative model for the insulin receptor, the decrease in insulin binding in the cells of the leprechaun infant and of patient A-l appears to be due to a decrease in receptor affinity. In both cases, this decrease in affinity was associated with an accelerated dissociation of bound [125I]insulin and a loss of negative cooperativity, i.e. dissociation was not accelerated by the addition of unlabeled hormone. In contrast, cells from patient A-3 showed no change in affinity, but demonstrated a reduction in apparent receptor number. Multiple other abnormalities of insulin receptor...