A genome-wide linkage scan for genes controlling variation in urinary albumin excretion in type II diabetes.

The main hallmark of diabetic nephropathy is elevation in urinary albumin excretion. We performed a genome-wide linkage scan in 63 extended families with multiple members with type II diabetes. Urinary albumin excretion, measured as the albumin-to-creatinine ratio (ACR), was determined in 426 diabetic and 431 nondiabetic relatives who were genotyped for 383 markers. The data were analyzed using variance components linkage analysis. Heritability (h2) of ACR was significant in diabetic (h2=0.23, P=0.0007), and nondiabetic (h2=0.39, P=0.0001) relatives. There was no significant difference in genetic variance of ACR between diabetic and nondiabetic relatives (P=0.16), and the genetic correlation (rG=0.64) for ACR between these two groups was not different from 1 (P=0.12). These results suggested that similar genes contribute to variation in ACR in diabetic and nondiabetic relatives. This hypothesis was supported further by the linkage results. Support for linkage to ACR was suggestive in diabetic relatives and became significant in all relatives for chromosome 22q (logarithm of odds, LOD=3.7) and chromosome 7q (LOD=3.1). When analyses were restricted to 59 Caucasian families, support for linkage in all relatives increased and became significant for 5q (LOD=3.4). In conclusion, genes on chromosomes 22q, 5q and 7q may contribute to variation in urinary albumin excretion in diabetic and nondiabetic individuals.

Variability in plasma prothrombin concentration: implications for use in epidemiology.

Recent evidence suggests a major role for prothrombin as a risk factor for thrombosis. However, estimating prothrombin levels from a deficient plasma-based clotting assay (factor IIc) is expensive and technically difficult in the setting of population-based research. We report the development of an enzyme-linked immunosorbent assay (ELISA) for prothrombin using purified antigen and polyclonal anti-prethrombin-1 IgG. Three different quality control plasmas had coefficients of variation (CV) of 6.5%, 4.9%, and 4.8%. Analytical recovery averaged 103.8%. Results from the ELISA correlated well with factor IIc results (r=0.75). The 5th-95th percentile range for healthy men (n=10) and women (n=16) was 97.7 pg/ml to 161.8 microg/ml. The assay exhibited no significant cross-reactivity with other vitamin-K-dependent proteins. Prothrombin showed no diurnal variation. In a study of biovariability the analytical variability, CV(A), was 3.1%; the within-subject variability, CV(I), was 7.3%; the between-subject variability, CV(G), was 14.5%. The critical difference for sequential values (i.e. the smallest percentage change unlikely to be due to CV(A) or CV(I)) significant at P=0.05 was 21.9%. The index of individuality, CV(I)/CV(G), was 0.50. On the basis of the overall biovariability data, primarily the index of individuality, prothrombin as measured in our ELISA is well suited for applications in population-based research.