Mutations in the insulin receptor gene in patients with genetic syndromes of insulin resistance and acanthosis nigricans

A novel insulin receptor mutation in an adolescent with acanthosis nigricans and hyperandrogenism

Insulin receptor mutations cause extreme insulin resistance resulting in acanthosis nigricans and hyperandrogenism. We report a pre-menarchal adolescent female with normal weight, with severe acanthosis nigricans, acne, and hirsutism. Initial investigation revealed elevated fasting and post-prandial insulin and high testosterone and androstenedione levels. Her father had frequent complaints of hypoglycemia. Coding sequence and splice junction analysis of the INSR gene, in our patient and her father, revealed a heterozygous missense mutation in the β subunit of the insulin receptor (Arg1131Trp), resulting in receptor loss of function. Metformin therapy and carbohydrate control improved acanthosis and menarche ensued within 3 months. Our case highlights the importance of distinguishing insulin resistance commonly associated with obesity from monogenic defects. Although, there is no consensus on treatment of children with monogenic forms of insulin resistance due to its rarity, dietary and lifestyle modifications and insulin-sensitizing agents play a key role in management.

Sequencing analysis of insulin receptor defects and detection of two novel mutations in INSR gene

Mutations in the insulin receptor gene cause the inherited insulin resistant syndromes Leprechaunism and Rabson–Mendenhall syndrome. These recessive conditions are characterized by intrauterine and post-natal growth restrictions, dysmorphic features, altered glucose homeostasis, and early demise. The insulin receptor gene (INSR) maps to the short arm of chromosome 19 and is composed of 22 exons. Here we optimize the conditions for sequencing this gene and report novel mutations in patients with severe insulin resistance.

Methods

PCR amplification of the 22 coding exons of the INSR gene was performed using M13-tailed primers. Bidirectional DNA sequencing was performed with BigDye Terminator chemistry and M13 primers and the product was analyzed on the ABI 3100 genetic analyzer. Data analysis was performed using Mutation Surveyor software comparing the sequence to a reference INSR sequence (Genbank NC_000019).

Results

We sequenced four patients with Leprechaunism or Rabson–Mendenhall syndromes as well as seven samples from normal individuals and confirmed previously identified mutations in the affected patients. Three of the four mutations identified in this group caused premature insertion of a stop codon. In addition, the INSR gene was sequenced in 14 clinical samples from patients with suspected insulin resistance and one novel mutation was found in an infant with a suspected diagnosis of Leprechaunism.

Discussion

Leprechaunism and Rabson–Mendenhall syndrome are very rare and difficult to diagnose. Diagnosis is currently based mostly on clinical criteria. Clinical availability of DNA sequencing can provide an objective way of confirming or excluding the diagnosis.

Pathogenesis of the metabolic syndrome: insights from monogenic disorders

Identifying rare human metabolic disorders that result from a single-gene defect has not only enabled improved diagnostic and clinical management of such patients, but also has resulted in key biological insights into the pathophysiology of the increasingly prevalent metabolic syndrome. Insulin resistance and type 2 diabetes are linked to obesity and driven by excess caloric intake and reduced physical activity. However, key events in the causation of the metabolic syndrome are difficult to disentangle from compensatory effects and epiphenomena. This review provides an overview of three types of human monogenic disorders that result in (1) severe, non-syndromic obesity, (2) pancreatic beta cell forms of early-onset diabetes, and (3) severe insulin resistance. In these patients with single-gene defects causing their exaggerated metabolic disorder, the primary defect is known. The lessons they provide for current understanding of the molecular pathogenesis of the common metabolic syndrome are highlighted.

Autoimmune hypoglycemia in a patient with characterization of insulin receptor autoantibodies

BACKGROUND

Type B insulin resistance syndrome is a manifestation of autoantibodies to the insulin receptor that results in severe hyperglycemia and acanthosis nigricans. However, the mechanisms by which these autoantibodies induce hypoglycemia are largely unknown. In this paper, we report the case of patient with type B insulin resistance syndrome who presented with frequent severe fasting hypoglycemia and acanthosis nigricans.

METHODS

To evaluate the mechanism of hypoglycemia, we measured the inhibition of insulin binding to erythrocytes and IM9 lymphocytes in a sample of the patient's dialyzed serum before and after immunosuppressive therapy.

RESULTS

In the patient's pre-treatment serum IgG, the binding of (125)I-insulin to erythrocytes was markedly inhibited in a dose-dependent manner until the cold insulin level reached 10(-9) mol/L. We also observed dose-dependent inhibition of insulin binding to IM9 lymphocytes, which reached approximately 82% inhibition and persisted even when diluted 1:20. After treatment with glucocorticoids, insulin-erythrocyte binding activity returned to between 70% and 80% of normal, while the inhibition of insulin-lymphocyte binding was reduced by 17%.

CONCLUSION

We treated a patient with type B insulin resistance syndrome showing recurrent fasting hypoglycemia with steroids and azathioprine. We characterized the patient's insulin receptor antibodies by measuring the inhibition of insulin binding.

Can geneticists help clinicians to understand and treat non-autoimmune diabetes?

Approximately, a few percent of the European population suffers from diabetes. Scientific evidence showed that specific treatment of this disease could be successfully tailored on the basis of proper differential diagnosis that in many instances also requires genetic testing. This may be helpful in achieving metabolic control of the disease, increasing quality of life and potentially reducing the prevalence of chronic complications. Identification of the molecular background of these specific forms of diabetes gives new insight into the underlying aetiology. This knowledge helps to optimize treatment in specific clinical situations. Monogenic diabetes is an excellent example of a clinical area where new advances in molecular genetics can aid patient care and treatment decisions. The most frequently diagnosed forms of monogenic diabetes are MODY, mitochondrial diabetes, permanent and transient neonatal diabetes (PNDM and TNDM). These rare forms probably constitute at least a few percent of all diabetes cases seen in diabetic clinics. The proper differential diagnosis also helps to predict the progress of diabetes in affected individuals and defines the prognosis in the family. Recently, several genome wide association studies added new facts to the knowledge on complex forms of type 2 diabetes mellitus (T2DM) as the scientists substantially extended the short list of previously identified genes. Most newly identified variants influence beta-cell insulin secretion, while a few modulate peripheral insulin action. It is not clear whether in the future the genetic testing of frequent polymorphisms will influence the treatment of T2DM. In this review, we present the clinical application of genetic testing in non-autoimmune diabetes, mostly monogenic forms of disease.

Monogenic diabetes: implications for therapy of rare types of disease

There are two major forms of diabetes: type 1 and type 2. However, monogenic diabetes, associated with severe beta-cell dysfunction or with severe resistance to insulin action, is diagnosed with increasing frequency by genetic testing. The list of such forms of diabetes includes MODY, mitochondrial diabetes, permanent neonatal diabetes (PNDM) and transient neonatal diabetes, familial lipodystrophies and some others. These rare forms constitute probably at least a few per cent of all diabetes cases seen in diabetic clinics. The identification of the molecular background of specific forms of diabetes gives new insight into the underlying aetiology. This knowledge helps to optimize treatment in specific clinical situations. The proper differential diagnosis also helps to predict the progress of diabetes in affected individuals and defines the prognosis in the family. For example, in patients with MODY2 because of glucokinase mutations who have very mild diabetes characterized by modest fasting, hyperglycaemia diet is frequently sufficient. Some other forms of monogenic diabetes associated with impaired function of the beta-cell, such as MODY3 and PNDM linked to mutations in Kir6.2 and SUR1 genes, can be successfully managed by sulphonylurea agents. Although the examples of pharmacogenetics seem to be less spectacular in rare syndromes of insulin resistance, those patients can also benefit from genetic testing. In this paper, the aetiology of some monogenic diabetes forms is reviewed together with the clinical aspects of management of the affected individuals.

Insulin receptor autoimmunity and insulin resistance

The frequency of insulin receptor autoantibodies (IR-ab) was determined among adolescents and young adults with documented insulin resistance syndrome (IRS) with and without concomitant autoimmunity. The study population was comprised of 61 patients with obesity, acanthosis nigricans and insulin resistance (simple IRS); 12 with IRS and other autoimmune problems (lupus erythematosus, rheumatoid arthritis, dermatomyositis) (type B insulin resistance); six with autoimmune polyglandular syndrome type 2; and 40 healthy controls. Using our newly developed radiobinding assay system, we found no control positive while 25% of the patients with type B IRS (3/12) were positive, as expected. However, we found that 9.8% of the patients with simple IRS (6/61) were also reproducibly positive. All the latter patients with positive IR-ab were female with ovarian hyperandrogenism. The phenotype of those affected was otherwise unremarkably different from those without IR-ab. Our findings suggest that autoimmunity to insulin receptors may be causal in IRS especially for females with ovarian hyperandrogenism, and that IR-ab may be found in IRS besides those previously defined by the type B phenotype. Determining the level of IR-ab in childhood onset IRS may provide mechanistic insights into the genesis of insulin resistance and lead to novel treatment approaches.

Clinical evaluation of insulin resistance and beta-cell function by the homeostasis model assessment in patients with systemic lupus erythematosus

The aim of this preliminary study was to evaluate insulin resistance and secretion using homeostasis model assessment (HOMA) in patients with systemic lupus erythematosus (SLE). The fasting glucose and insulin concentrations, HOMA insulin resistance (IR), HOMA beta-cell, antidouble-stranded DNA antibodies (anti-dsDNA), C3, C4, and SLE disease activity index (SLEDAI) were determined in a total of 58 female SLE patients. All patients were classified into subgroups according to the presence of anticardiolipin antibodies (aCL+ vs. aCL-) and SLEDAI scores (SLEDAI < 3 vs. SLEDAI > 3). Results showed that SLE patients with and without aCL had significantly higher fasting insulin levels, HOMA IR, and HOMA beta-cells than controls. Similar results were also found in SLE patients with different disease activities. Pearson's correlation analysis showed that there was a highly significant correlation of HOMA IR with fasting insulin concentration in the SLE patients and SLE subgroups overall. However, HOMA beta-cells were positively correlated with HOMA IR and fasting insulin level, but negatively correlated with fasting glucose concentration in SLE patients overall. In conclusion, SLE patients, regardless of the presence of aCL and different disease activities, had a higher risk of insulin resistance and abnormal insulin secretion than age-matched healthy controls, based on fasting insulin concentration, HOMA IR, and HOMA beta-cells.

Relation of acanthosis nigricans to hyperinsulinemia and insulin sensitivity in overweight African American and white children

OBJECTIVES

Acanthosis nigricans (AN) has been proposed as a reliable marker of hyperinsulinemia, but its utility for predicting hyperinsulinism has not been systematically evaluated in overweight children. We examined the relationship of AN to hyperinsulinemia and body adiposity.

STUDY DESIGN

One hundred thirty-nine children underwent physical examination for AN, body composition studies, an oral glucose tolerance test, and a hyperglycemic clamp.

RESULTS

Thirty-five children (25%) had AN. AN was more prevalent in African Americans (50.1%) than in white subjects (8.2%, P < .001). Independent of race, children with AN had greater body weight and body fat mass (P < .001); greater basal and glucose-stimulated insulin levels during oral glucose tolerance test (P < .001); greater first-phase, second-phase, and steady-state insulin levels (P < .001); and lower insulin sensitivity (P < .001) during the hyperglycemic clamp. After adjusting for body fat mass and age, none of these differences remained significant. When categorized by fasting insulin, 35% with fasting insulin levels > 20 microU/mL and 50% with fasting insulin levels > 15 microU/mL did not have AN. Eighty-eight percent of children with fasting insulin levels > or = 15 microU/mL had a body mass index SD score > or = 3.0.

CONCLUSIONS

AN is not a reliable marker for hyperinsulinemia in overweight children. Children with a race-, sex-, and age-specific body mass index SD scores > or = 3.0 should be screened for hyperinsulinemia, whether or not they have AN.

Partial face-sparing lipodystrophy (Köbberling-Dunnigan syndrome): report of a sporadic case

A sporadic case is presented of a 20-year-old female with partial face-sparing lipodystrophy, also known as the Köbberling-Dunnigan syndrome with the Type 1 clinical phenotype. This disorder affects the limbs and spares the face. The trunk is spared in the Type 1 phenotype but is affected in the Type 2 phenotype. The patient had the associated features of this syndrome including the hyperinsulinaemia, acanthosis nigricans and mildly raised triglycerides, but not diabetes mellitus.

Acanthosis nigricans associated with hepatolenticular degeneration

Acanthosis nigricans and hepatolenticular degeneration (Wilson's disease) developed simultaneously in a 16-year-old boy. The diagnosis of Wilson's disease was based on the clinical presentation, including Kayser-Fleischer ring, hypoceruloplasminemia, hypocupremia, and hypercupriuria. His skin lesions were characterized by thick, dark brown, verrucous plaques on the dorsa of both feet, the neck, axillae, and groin. The histological findings were compatible with acanthosis nigricans. Six months after treatment with D-penicillamine, two grams per day, his skin lesions and neurological symptoms were much improved and no complications were observed.

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.