Figure 929

Example of the use of gene linkage to identify ADPKD gene carriers among generation IV of a PKD1 family. Two markers flanking the PKD1 gene were used. The first one (3' HVR) has six possible alleles (1 through 6) and the other (p 26.6) is biallelic (a, b). In this family, the haplotype 2a is transmitted with the disease (see affected persons II5, III1, and III3). Thus, IV4 has a 99% chance of being a carrier of the mutated PKD1 gene, whereas her sisters (IV1, IV2, IV3) have a 99% chance of being disease free.

Until direct gene testing for PKD1 and PKD2 is readily available, genetic diagnosis will rest on gene linkage. Such analysis requires that other affected and unaffected family members (preferably from two generations) be available for study. Use of markers on both sides of the tested gene is required to limit potential errors due to recombination events. Linkage to PKD1 is to be tested first, as it accounts for about 85% of cases.

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