2 MUTATIONS IN THE INSULIN-RECEPTOR GENE OF A PATIENT WITH LEPRECHAUNISM - APPLICATION TO PRENATAL-DIAGNOSIS

Leprechaunism is an autosomal recessive disorder caused by mutations i n the insulin receptor gene and characterized by intrauterine and post natal growth restriction, abnormal glucose homeostasis, and severe ins ulin-resistance. Here we report the biochemical and molecular characte rization of a male patient, NZ, who died at 2 yr of age with this synd rome. I-125-Insulin binding to fibroblasts from the proband, his mothe r, father, and unaffected sister was reduced to 8, 53, 38, and 35% of controls, respectively. Analysis of the insulin receptor gene by polym erase 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 p airs 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 nuc leotide of the splice-donor junction in intron 13. The maternal mutati on activated a cryptic splice site 27 base pairs upstream in exon 13 a nd caused an in-frame deletion of amino acids 859-867 of the extracell ular domain of the insulin receptor beta subunit. Identification of bo th mutations enabled prenatal diagnosis in 2 subsequent pregnancies. I n the first pregnancy, DNA from cells cultured from chorionic villus ( CV) biopsies carried both mutations in the insulin receptor gene. In t he second pregnancy, DNA from the CV biopsy cells was negative for bot h mutations, indicating that the fetus was unaffected by leprechaunism . Insulin binding could not be used in prenatal diagnosis because cell s cultured from some control CV biopsies failed to bind insulin. These data indicate that patient NZ with leprechaunism was a compound heter ozygote for 2 novel mutations in the insulin receptor gene and that di rect DNA sequencing enables prenatal diagnosis for this lethal disorde r.