RESUMEN
BACKGROUND: Insulin receptor substrate-1 (IRS-1) is an endogenous substrate for the insulin receptor tyrosine kinase, which plays an important role in insulin signaling. Mutations in the IRS-1 gene are associated in some populations with obesity and Type 2 diabetes. METHODS: To determine whether variation in the IRS-1 gene contributes to genetic susceptibility to insulin resistance and Type 2 diabetes in Mexican Americans, the entire coding region of the IRS-1 gene was screened for variation in 31 unrelated subjects with Type 2 diabetes using single-stranded conformational polymorphism analysis (SSCP) and dideoxy sequence analysis. Variants encoding amino acid substitutions were genotyped in 27 unrelated nondiabetic Mexican Americans and in all family members of subjects containing these variants, and association analyses were performed. To trace the ancestral origins of the variants, Iberian Caucasians and Pima Indians were also genotyped. RESULTS: Eight single base changes were found: four silent polymorphisms and four missense mutations (Ala94Thr, Ala512Pro, Ser892Gly and Gly971Arg). Allele frequencies were 0.009, 0.017, 0.017 and 0.043, respectively. There were no significant associations of any of these variants with diabetes, glucose or insulin levels during an oral glucose tolerance test, or with body mass index (BMI) in Mexican American families except for a modest association between the Ala94Thr variant and decreased BMI (30.4 kg/m(2) vs 24.0 kg/m(2); p=0.035). None of these four missense mutations were detected in Pima Indians. In Iberian Caucasians, neither Ala94Thr nor Ser892Gly were detected, and Ala512Pro was detected in only 0/60 diabetic patients and 1/60 nondiabetic controls. Gly971Arg was relatively more common in Iberian Caucasians with 12/58 diabetic patients and 7/60 nondiabetic controls being heterozygous for this variant (p=0.21 for comparison between diabetic and nondiabetic subjects). CONCLUSIONS: Ala94Thr, Ala512Pro and Ser892Gly mutation are rare in the populations studied. Gly971Arg, is more common in Mexican Americans and Caucasians, but is not a major contributor to genetic susceptibility to Type 2 diabetes.
Asunto(s)
Diabetes Mellitus Tipo 2/genética , Variación Genética , Americanos Mexicanos/genética , Fosfoproteínas/genética , Mutación Puntual , Polimorfismo Conformacional Retorcido-Simple , Adulto , Anciano , Sustitución de Aminoácidos , Familia , Femenino , Genotipo , Humanos , Proteínas Sustrato del Receptor de Insulina , Masculino , Persona de Mediana Edad , Linaje , Reacción en Cadena de la Polimerasa , TexasRESUMEN
Peroxisome proliferator-activated receptors (PPAR) are transcription factors that regulate adipocyte differentiation and gene expression. We tested the hypothesis that the Pro12Ala variant of PPAR-gamma2 is associated with obesity and type 2 diabetes-related traits in 921 subjects from the San Antonio Family Heart Study. Subjects with at least one Ala allele (n=210) had significantly higher body mass index (P=0.015) and waist circumference (P=0.028) and significantly higher levels of serum leptin (P= 0.022) than those without the allele. Further studies will determine whether the Pro12Ala variant itself, or other genetic variation at PPAR-gamma, is responsible for this association with measures of obesity in Mexican Americans.
Asunto(s)
Americanos Mexicanos/genética , Obesidad/genética , Receptores Citoplasmáticos y Nucleares/genética , Factores de Transcripción/genética , Población Blanca/genética , Adulto , Índice de Masa Corporal , Femenino , Humanos , Leptina/genética , Masculino , TexasRESUMEN
The beta3 adrenergic receptor, located on chromosome 8, is a regulator of energy expenditure and lipolysis. A missense mutation in this gene, characterized by the replacement of tryptophan by arginine at codon 64 (Trp64Arg), is associated with obesity in some studies. We examined the effect of this variant on obesity in Mexican Americans, using a paired sibling design to minimize variability due to genetic background and a previously identified major susceptibility locus for obesity. We identified 45 sib-pairs that were concordant (identical by descent) for a locus on chromosome 2 which we have shown previously to be tightly linked to obesity in this population. The Trp64Arg variant, detected by PCR-restriction fragment length polymorphism analysis, was present in one sibling within each of the 45 sib-pairs. Presence of the variant was associated with significantly higher values in body mass index (P = 0.04), fat mass (P = 0.04), and waist circumference (P = 0.05). We conclude that the Trp64Arg variant is associated with obesity in this Mexican American population. The paired sibling design probably enhanced our ability to detect the effects of this variant by allowing us to account for variation attributable to another obesity susceptibility locus and to background genes.
Asunto(s)
Arginina/genética , Americanos Mexicanos , Obesidad/genética , Receptores Adrenérgicos beta/genética , Triptófano/genética , Adulto , Variación Genética , Humanos , Receptores Adrenérgicos beta 3RESUMEN
The beta 3-adrenergic receptor (beta 3AR) is expressed in visceral fat and is a regulator of resting metabolic rate, thermogenesis, and lipolysis. We genotyped 61 unrelated Mexican Americans for a variant in the beta 3AR gene (codon 64 TGGTrp-->CGGArg; TRP64ARG). The allele frequency was 0.13. The TRP64ARG variant was significantly associated with an earlier age of onset of non-insulin-dependent diabetes mellitus (41.3 +/- 4.6 years vs 55.6 +/- 2.6 years; P < 0.02) and in non-diabetics, with elevated 2-h insulin levels during an oral glucose tolerance test (810 +/- 120 pmol/l vs 384 +/- 6 pmol/l; P < 0.005). Non-diabetic subjects with the variant allele tended to have higher body mass indices (BMI), waist-to-hip ratios, and diastolic blood pressures. The study group was expanded to include 421 related subjects from 31 families in the San Antonio Family Diabetes Study. Using a measured genotype analysis approach to estimate genotype-specific means for each trait, those who were homozygous for the TRP64ARG variant had significantly higher 2-h insulin levels (P = 0.036) and trends towards higher BMI compared to the other two genotypes. We detected no associations of these traits in the TRP64ARG heterozygotes in the larger group. We conclude that the TRP64ARG beta 3AR variant is a susceptibility gene for several features of the insulin resistance syndrome in Mexican Americans. Since its effects are modest, study design (e.g., subject selection, genetic background, and statistical analyses) may influence which traits are associated with this variant and whether or not the effect is detectable in heterozygotes.