A SPECTRUM OF MUTATIONS IN THE POLYCYSTIC KIDNEY DISEASE-2 (PKD2) GENE FROM 8 CANADIAN KINDREDS

Autosomal dominant polycystic kidney disease (ADPKD) is a common Mende lian disorder that affects approximately 1 in 1000 live births. Linkag e studies have shown that the majority (approximately 85%) of cases ar e due to mutations in PKD1 on chromosome 16p, while mutations in PKD2 on chromosome 4q account for most of the remaining cases. Locus hetero geneity in ADPKD is known to contribute to differences in disease seve rity, with PKD1-linked families having earlier onset of end-stage rena l disease (ESRD) than PKD2-linked families (mean age at ESRD: 56 versu s 70, respectively). In this study, 11 Canadian families with ADPKD we re screened for PKD2 mutations. In four families, linkage to PKD2 was previously documented. In the remaining seven smaller families, one or more affected members had late-onset ESRD at age 70 or older. Using s ingle-stranded conformational polymorphism analysis, one affected memb er from each family was screened for mutations in all 15 exons of PKD2 , which were PCR-amplified from genomic templates. A spectrum of mutat ions was found in approximately 73% (8 of 11) of the families screened , with no difference in the detection rate between the PKD2-linked fam ilies and the families with late-onset ESRD. In three unrelated famili es, insertion or deletion of an adenosine in a polyadenosine tract (i. e., (A)(8) at nt 2152-2159) was found on exon 11, suggesting that this mononucleotide repeat tract is prone to mutations from ''slipped stra nd mispairing.'' All mutations, scattered between exons 1 and 11, are predicted to result in a truncated polycystin 2 that lacks both the ca lcium-binding EF-hand domain and the two cytoplasmic domains required for the interaction of polycystin 2 with polycystin 1 and with itself. Furthermore, no correlation was found between the location of the mut ations in the PKD2 coding sequence and disease severity. Thus, these f indings are consistent with other recently published reports and sugge st that most PKD2 mutations are inactivating.