Because NIDDM is heterogeneous and perhaps polygenic in nature, these linkage analyses in families with NIDDM can be extended to other genes when they are cloned such as that coding for the insulin receptor.
Although no significant association of restriction fragment length polymorphism with Type 2 diabetes was found in the present study, our results suggest that the restriction fragment length polymorphism in the human insulin receptor gene varies among ethnic groups, and that the restriction fragment length polymorphism linked to the human insulin receptor gene might be a useful marker for the linkage study of the genes located close to the human insulin receptor gene on chromosome 19.
We conclude that the tyrosine kinase activity of the skeletal muscle insulin receptor is defective in obesity and Type 2 diabetes, and that this alteration contributes to the insulin-resistant characteristics of both disorders.
A genetic analysis of diabetic and non-diabetic Punjabi Sikhs (n = 164) was made for markers of non-insulin-dependent diabetes mellitus using insulin receptor, insulin, and HLA-D alpha chain gene probes.
Nevertheless, it may indicate that insulin resistance functionally related to an insulin-receptor gene polymorphism is the proximal cause of NIDDM in at least one subset of the population.
This raises the possibility that mutations in the insulin receptor gene may account for the insulin resistance in some patients with non-insulin-dependent diabetes mellitus.
We therefore characterized restriction-fragment-length polymorphisms of the insulin-receptor gene with the restriction enzyme Rsa 1 in 242 Mexican Americans and non-Hispanic Whites with type II diabetes and 202 age-, sex-, and ethnicity-matched control subjects who participated in a population-based study in San Antonio.
The analysis of the INSR locus revealed "protective" haplotypes, and it may be possible to use two of the INSR haplotypes as genetic markers to identify individuals having a very low probability of developing NIDDM regardless of the presence of other genes conferring susceptibility to this disorder.
Because the nature and location of the insertion did not suggest a role in insulin-receptor function, the association of this RFLP with NIDDM and hyperinsulinemia was reexamined in a small sample of Whites.
To directly address the question of potential insulin-receptor genetic defects in Pima Indians, we isolated and sequenced insulin-receptor cDNA from two Pima Indians with NIDDM.
We investigated intracellular processing of the insulin-receptor complex in monocytes from 12 healthy control subjects, 11 obese nondiabetic subjects, and 13 obese patients with non-insulin-dependent diabetes mellitus (NIDDM) by measuring receptor internalization, recovery of cell-surface insulin binding after receptor internalization, and the release of intracellular intact insulin (insulin retroendocytosis).
Defects in insulin-receptor function have been associated with insulin-resistant states such as obesity and non-insulin-dependent diabetes mellitus (NIDDM).
To investigate the potential of the technique for screening many patients, the 5 exons that encode the tyrosine kinase domain of the insulin receptor were examined in 30 unrelated white subjects with non-insulin-dependent diabetes mellitus (NIDDM).
Each pedigree was initially examined with insulin receptor restriction fragment length polymorphisms to determine whether any allele segregated with Type 2 diabetes in these pedigrees.
The significance of insulin receptor gene variants in the aetiology of Type 2 (non-insulin-dependent) diabetes mellitus has been investigated by analysis of restriction fragment length polymorphisms in a genetically homogeneous Swedish population.
From these studies, we conclude that the insulin resistance seen in the great majority of subjects with the common form of NIDDM is not due to genetic variation in the coding sequence of the IR beta subunit, nor to any single mutation in the GLUT-4 gene.
In an attempt to elucidate whether structural defects in the insulin receptor could be a primary cause of insulin resistance in NIDDM, we analyzed the insulin-receptor cDNA sequence in a subject with NIDDM who is also homozygous for this RFLP.
We have recently examined the exons encoding the insulin receptor tyrosine kinase domain and GLUT 4 in 30 subjects with Type 2 (non-insulin-dependent) diabetes mellitus using a molecular scanning approach.
The possibility that the insulin receptor and GLUT4 may be candidate genes for inherited insulin resistance in NIDDM has been addressed with the aid of genetic screening techniques such as SSCP.
Identification of a mutation in the insulin receptor gene in a patient with a moderate degree of insulin resistance associated with morbid obesity suggests that insulin receptor mutations may exist in patients with Type 2 (non-insulin-dependent) diabetes mellitus associated with a moderate degree of insulin resistance.
The usefulness of these adaptations is illustrated by their application to the simultaneous detection of three point mutations, two in the tyrosine kinase domain of the insulin receptor and one in the insulin-responsive glucose transporter (GLUT4) in a highly insulin-resistant NIDDM population.