Narrowing of the autosomal recessive polycystic kidney disease critical region in a Newfoundland family

A Newfoundland family, consisting of three nuclear families, was identified as having polycystic kidney and liver disease and found to be descended from two founding ancestral pairs. Using homozygosity mapping with polymorphic microsatellite markers, three disease loci, NPH-1, -2 and mouse bpk/jcpk were excluded and linked the disease in sibships A and B to the ARPKD disease loci on chromosome 6. Due to a meiotic recombination in one of the individuals in sibship A, the ARPKD critical region was narrowed to a 1cM region. The disease in sibship C was not linked to either of the abovementioned loci and kidney ultrasound suggested that the disease was not ADPKD. Because the gene which causes ARPKD is, as yet, unknown, it was necessary to attempt to identify it through positional cloning. A PAC contiguous map was constructed to allow the examination of smaller, individual pieces of DNA within the region. Each clone was subcloned and screened for microsatellites. Three were identified however none was variable in this family. The complete sequence of clone 108c2 had been published to the public domain and examination revealed a large repeat region which was analyzed and found to be polymorphic. This marker allowed the ARPKD region to be further refined to an area of approximately 560kb in size, completely covered by PAC clones. This region contains 10 known gene-oriented clusters representing different transcripts including NFYA, TFAP2B, MDFI and APOBEC2 (http://www.ncbi.nlm.nih.gov/ UniGene).