Novel COL4A4 splice defect and in-frame deletion in a large consanguine family as a genetic link between benign familial haematuria and autosomal Alport syndrome.
BACKGROUND
Alport syndrome (AS) is a common hereditary cause for end-stage renal failure due to a defect in type IV collagen genes. The molecular pathogenesis of benign familial haematuria (BFH) is not fully understood. Evidence from linkage analyses and mutation studies point to a role of the COL4A3/COL4A4 genes. The present study describes molecular changes of the COL4A4 gene that cause both diseases: autosomal recessive AS and BFH in a consanguine family with a 400-year-old history of haematuria.


METHODS
RNA and DNA were isolated and analysed by RT-PCR, PCR, DNA and cDNA sequencing, and Southern blotting. Evaluation of family members comprised creatinine clearence, urine analysis, audiometry and past medical history.


RESULTS
Forefathers of this family moved to a German village in the 17th century. Sporadic episodes of macrohaematuria have been reported ever since. Numerous family members with haematuria including the parents of the index family were heterozygous for a splice defect eliminating exon 25 from the alpha4(IV) cDNA. The daughter (15 years old, creatinine clearence 27 ml/min, proteinuria 5 g/day, hearing loss) was homozygous for the mutation, while the son (22 years old, creatinine clearance 68 ml/min, proteinuria 11 g/day, hearing loss, splitted and thickened glomerular basement membrane) was heterozygous. Further analysis showed a second mutation, an 18 bp in-frame deletion in exon 25, for which numerous family members were heterozygous, and both children were homozygous.


CONCLUSIONS
The COL4A4 splice defect causes BFH-phenotype in heterozygous, and AS in homozygous state. The clinical spectrum of heterozygous individuals reaches from macrohaematuria, intermittent microhaematuria to isolated deafness. The 18 bp in-frame deletion aggravates the phenotype in the compound heterozygous son. These results give further evidence that BFH and autosomal AS are in fact both type IV collagen diseases.
Gross
Oliver
O
Medical Faculty University of Cologne, Cologne General Hospital, Department of Internal Medicine I, Merheim Medical Center, Cologne, Germany. oliver.gross@uni-koeln.de
Netzer
Kai-Olaf
KO
Lambrecht
Romy
R
Seibold
Stefan
S
Weber
Manfred
M
D000293:Adolescent; D000328:Adult; D024141:Collagen Type IV / Q000235:genetics*; D003241:Consanguinity; D004252:DNA Mutational Analysis; D005260:Female; D017353:Gene Deletion; D008040:Genetic Linkage; D005838:Genotype; D005858:Germany; D006417:Hematuria / Q000235:genetics*; D006801:Humans; D007668:Kidney / Q000473:pathology; D008297:Male; D008969:Molecular Sequence Data; D009394:Nephritis, Hereditary / Q000235:genetics*; D010375:Pedigree; D010641:Phenotype; D020133:Reverse Transcriptase Polymerase Chain Reaction
C466620:COL4A4 protein, human; D024141:Collagen Type IV