X-linked Alport syndrome in Hellenic families: phenotypic heterogeneity and mutations near interruptions of the collagen domain in COL4A5.

The X-linked Alport syndrome (ATS) is caused by mutations in COL4A5 and exhibits a widely variable expression. Usually ATS is heralded with continuous microhematuria which rapidly progresses to proteinuria, hypertension and chronic or end-stage renal disease (ESRD) by adolescence, frequently accompanied by sensorineural deafness and ocular complications. Milder forms of ATS also exist. We studied 42 patients (19M, 23F) of nine Hellenic families suspected clinically of X-linked ATS who presented with marked phenotypic heterogeneity. We identified mutations in COL4A5 in six families. Two males with nonsense mutation E228X reached ESRD by ages 14 and 18. Frameshift mutation 2946delT followed the same course with early onset renal involvement and deafness. However, two males with the milder missense mutation G624D, reached ESRD after 39 years and one patient showed thin basement membrane nephropathy (TBMN). Another 5/8 affected males with missense mutation P628L also developed ESRD between 30 and 57 years, while three exhibit only mild chronic renal failure (CRF). The data support previous findings that certain mutations are associated with milder phenotypes and confirm that mutation G624D may be expressed as TBMN with familial hematuria. Similar conclusions apply for missense mutation P628L. Interestingly, mutations G624D and P628L are near the 12th natural interruption of COL4A5 triple helical domain, which may explain the milder phenotype.

Thin glomerular basement membranes in patients with hematuria and minimal change disease.

A detailed morphometric analysis of glomerular basement membrane (GBM) thickness was carried out on biopsies from 16 patients exhibiting normal histology and unremarkable immunofluorescence. Eleven of these patients presented with proteinuria, 8 in the nephrotic syndrome range, while 5 had hematuria as well. The remaining 5 patients presented with hematuria only. Eight patients had an initial diagnosis of minimal change disease, 4 were diagnosed as thin-membrane nephropathy, 2 had Alport syndrome, and the remaining 2 had hypertensive nephropathy. Quantitative morphometric analysis of GBM identified 3 subsets of patients. The first subset consisted of 6 patients: 5 adults, with an average GBM width of 361 +/- 34 nm, and 1 child. The second subset included 8 patients with thin GBMs and a mean thickness of 253 +/- 15 nm. The last subset comprised 2 patients with Alport syndrome showing marked variability in GBM thickness. This study has confirmed the presence of thin GBMs in hematurics, but has also revealed GBM thinning in 50% of patients with a diagnosis of minimal change disease.