Computational Analysis of Damaging Single-Nucleotide Polymorphisms and Their Structural and Functional Impact on the Insulin Receptor.

Single-nucleotide polymorphisms (SNPs) associated with complex disorders can create, destroy, or modify protein coding sites. Single amino acid substitutions in the insulin receptor (INSR) are the most common forms of genetic variations that account for various diseases like Donohue syndrome or Leprechaunism, Rabson-Mendenhall syndrome, and type A insulin resistance. We analyzed the deleterious nonsynonymous SNPs (nsSNPs) in INSR gene based on different computational methods. Analysis of INSR was initiated with PROVEAN followed by PolyPhen and I-Mutant servers to investigate the effects of 57 nsSNPs retrieved from database of SNP (dbSNP). A total of 18 mutations that were found to exert damaging effects on the INSR protein structure and function were chosen for further analysis. Among these mutations, our computational analysis suggested that 13 nsSNPs decreased protein stability and might have resulted in loss of function. Therefore, the probability of their involvement in disease predisposition increases. In the lack of adequate prior reports on the possible deleterious effects of nsSNPs, we have systematically analyzed and characterized the functional variants in coding region that can alter the expression and function of INSR gene. In silico characterization of nsSNPs affecting INSR gene function can aid in better understanding of genetic differences in disease susceptibility.

Síndrome de insulinorresistencia severa tipo A debido a mutación del gen del receptor de insulina / Severe type A insulin resistance syndrome due to a mutation in the insulin receptor gene

Los síndromes monogénicos de insulinorresistencia sin lipodistrofia constituyen un rupo de entidades infrecuentes que incluyen los síndromes de Donohue o leprechaunismo, Rabson-Mendenhall y resistencia a la insulina tipo A. Se caracterizan por un amplio espectro fenotípico que asocia insulinorresistencia extrema y alteraciones hidrocarbonadas de grado variable. Presentamos un caso de resistencia a la insulina tipo A, caracterizado por resistencia insulínica grave, acantosis nigricans e hiperandrogenismo, debido a una mutación en heterocigosis en el xón 19 del gen del receptor de insulina que codifica para el dominio tirosinquinasa. Se destaca la elevada morbilidad de dicha entidad, a pesar de incluirse dentro del espectro menos grave de los síndromes genéticos de resistencia insulínica, así como la ausencia de una terapia satisfactoria. El estudio molecular revela el diagnóstico e informa del pronóstico y la supervivencia, factores ligados a la función residual del receptor, además de contribuir al desarrollo de nuevas dianas terapéuticas

Insulin resistance syndromes without lipodystrophy are an infrequent and heterogeneous group of disorders with variable clinical phenotypes, associated with hyperglycemia and hyperinsulinemia. The three conditions related to mutations in the insulin receptor gene are leprechaunism or Donohue syndrome, Rabson-Mendenhall syndrome, and Type A syndrome. A case is presented on a patient diagnosed with type A insulin resistance, defined by the triad of extreme insulin resistance, acanthosis nigricans, and hyperandrogenism, carrying a heterozygous mutation in exon 19 of the insulin receptor gene coding for its tyrosine kinase domain that is crucial for the catalytic activity of the receptor. The molecular basis of the syndrome is reviewed, focusing on the structure-function relationships of the insulin receptor, knowing that the criteria for survival are linked to residual insulin receptor function. It is also pointed out that, although type A insulin resistance appears to represent a somewhat less severe condition, these patients have a high morbidity and their treatment is still unsatisfactory

[Donohue syndrome or leprechaunism]. / Le syndrome de Donohue ou lepréchaunisme : à propos d'un cas.

Donohue syndrome or leprechaunism is a severe congenital insulin-resistance syndrome. It is characterized by intra-uterine and neonatal growth retardation, typical dysmorphic features, and metabolic abnormalities with hyperinsulinism and hyperandrogenism. Problems in energy metabolism and loss of glucose homeostasis are responsible for early death in the first year of life. We describe a case with a novel homozygote mutation in the insulin receptor gene. This patient had hypertrophic cardiomyopathy with heart failure and bronchial compression leading to clinical deterioration over 5 days and subsequently death. A treatment with recombinant IGF-1 was tried without efficacy.

Areolar sebaceous hyperplasia with underlying primary duct carcinoma of the breast in a woman with Donohue syndrome (leprechaunism).

Areolar hyperplasia is only reported when exaggerated, and even so, exaggerated areolar sebaceous hyperplasia is rare. We have recently seen a case of areolar sebaceous hyperplasia in a 32-year-old woman with Donohue syndrome (leprechaunism), who also had an invasive ductal carcinoma in the same breast. The patient showed typical "elfin-like" face with wide nostrils and thick lips, large and low-set ears, and dysplastic nails. The areola showed a yellowish thickened plaque of 5-cm diameter that corresponded to a hyperplasia of the sebaceous glands. Immunohistochemistry for the mismatch repair proteins (MLH1, MSH2, MSH6, and PMS2) was performed on the sebaceous hyperplasia and on the breast carcinoma, and no lack of expression of the markers was evidenced. We have found no other reported case of areolar sebaceous hyperplasia either in cases of breast carcinoma or in cases of leprechaunism.

Rabson-Mendenhall syndrome: two case reports and a brief review of the literature.

Rabson-Mendenhall syndrome is a rare, autosomal recessive disorder characterized by insulin resistance syndrome, growth retardation, coarse and senile-looking faces, mental precocity, early dentition, and pineal hyperplasia. Mutations of the insulin receptor gene affecting insulin action appear to be the basic mechanism underlying this syndrome. We report on Rabson-Mendenhall syndrome in two siblings and briefly review the literature.

Downregulation of Wnt-mediated ROS generation is causally implicated in leprechaunism.

Although mutations in the insulin receptor have been causally implicated with leprechaunism, the full pathophysiology of the syndrome cannot be accounted for by malfunction of this gene alone. We sought to characterize a connection between Wnt-mediated cell signaling and the production of reactive oxygen species (ROS) which revealed a novel mechanistic basis for understanding the pathogenesis of leprechaunism. To identify candidate genes involved in this process, a PCR-based subtractive hybridization was performed. Candidate genes were examined for interaction with the Wnt signaling pathway and ROS generation. We found that Dickkopf 1 (Dkk1), a Wnt inhibitor, is overexpressed in skin fibroblast cells derived from three leprechaunism patients and that the cells showed an impaired response to Wnt2 in terms of beta-catenin-Tcf activation. Knockdown of Dkk1 in the patient cell lines rescued Wnt2-mediated Tcf activation. Concerted action of Wnt2 and knockdown of Dkk1 resulted in enhanced Nox4 expression and PDGF-induced ROS generation compared to parental patient cells. Furthermore, we found that NFATc2 was activated in response to Wnt2 stimulation and directly activates Nox4 expression. These data show a crosstalk between Wnt and ROS pathways which in turn provides new mechanistic insights at the molecular level into the pathogenesis of leprechaunism.