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Genetic heterogeneity among kindreds with Alport syndrome
Abstract:
Twenty-three kindreds were ascertained through patients at renal clinics at University of Utah Associated Hospitals. Urinalysis indicated glomerulonephritis in 231 of 997 examined kindred members; medical records documented kidney disease consistent with glomerulonephritis in 88 unexamined kindred members. Renal biopsies of 35 persons in a subset of 14 kindreds showed ultrastructural changes and absence of immune phenomena consistent with the diagnosis of Alport syndrome. End-stage renal disease (ESRD) had occurred in 72 (49%) of 148 known affected males and in 13 (8%) of 171 known affected females. No father-son affected pairs occurred in any of the kindreds; 84% of daughters of affected fathers were affected, and 49% of sons and 48% of daughters of affected mothers were affected. One of three phenotypes (juvenile Alport syndrome with deafness, adult Alport syndrome with deafness, or adult Alport syndrome without deafness or other defects) occurred in each of the 23 kindreds. We applied likelihood analysis to test for genetic heterogeneity underlying the phenotypic heterogeneity. In the first application (the admixture test), we tested for the occurrence of two forms of the disease without specifying which kindred had which form; we found insufficient evidence of admixture. In the second application (the predivided-sample test), we tested for genetic heterogeneity expressed as phenotypic heterogeneity. Kindreds were successively divided into two subgroups, with admission to the first subgroup dependent upon: (1) having greater than or equal to 2 males with ESRD, (2) occurrence of deafness in most nephrologically affected male family members, and (3) intrakindred mean age of ESRD in males later than age 31. Weak evidence of heterogeneity was found for category (1); stronger evidence of heterogeneity was found for category (3). Penetrance of microscopic hematuria in female heterozygotes was estimated as 82% overall, 85% for adult Alport syndrome, and 28% for juvenile Alport syndrome.