As we mentioned earlier, ARPKD is caused by mutations in
PKHD1 and, the recently discovered,
DZIP1L [25][26][27].
PKHD1, located on chromosome 6 (6p12.3-p12.2) (Figure 2A)
[21][27][28][29], is one of the largest human genes with a genomic segment of ~500 kb. It is predicted to have a minimum of 86 exons assembled in a complicated pattern of alternative splice variants, transcribing a large full-length mRNA of approximately 8.5 kb–13 kb
[28]. Multiple types of mutations characterized as pathogenic have been identified across the gene. Currently, approximately 750
PKHD1 mutations have been identified, of which approximately half are missense changes. A missense mutation in exon 3 (c. 107C>T; p.Thr36Me) is the most common mutation described, accounting for more than 20% of all cases
[21][30]. This mutation has been observed in the context of heterozygotes, with a second distinct mutant allele
[31]. Most cases are familial, but de novo mutations are also reported and account for 2 to 5% of cases
[21]. Interestingly, in the context of isolated autosomal dominant polycystic liver disease (ADPLD), Besse and colleagues have reported several individuals with
PKHD1 mutations in heterozygote carriers, 10 of 102 ADPLD patients of their cohort were explained by
PKHD1 mutations, one of them presented the p.Thr36Me missense variant
[32]. According to the clinical observation, it is a genetic fact that 10% of ARPKD patients present innumerable asymptomatic liver cysts
[33]. However, the data are not sufficient to explain why
PKHD1 in ARPKD leads to severe hepatic and renal phenotype, but not in ADPLD; in this regard, more studies are needed
[34].