A form of adult polycystic kidney disease that is inherited as an autosomal dominant and is seemingly phenotypically identical to the chromosome 16-linked PKD1 (601313) has been observed in several kindreds. Kimberling et al. (1988) described a 5-generation ... A form of adult polycystic kidney disease that is inherited as an autosomal dominant and is seemingly phenotypically identical to the chromosome 16-linked PKD1 (601313) has been observed in several kindreds. Kimberling et al. (1988) described a 5-generation kindred, descendants of Sicilian immigrants to the United States, in which autosomal dominant polycystic kidney disease occurred without linkage to the alpha-hemoglobin complex. The frequency of recombination exceeded 24%. Clinical findings in this family were indistinguishable from those in other families with the linked disease. Kumar et al. (1990) presented linkage studies in the large family reported by Kimberling et al. (1988), which excluded the locus from about 61% of chromosome 1, including segments of the long and short arms. Romeo et al. (1988) described another Italian family with autosomal dominant polycystic kidney disease unlinked to the alpha-hemoglobin complex. On the basis of linkage studies, Pieke et al. (1989) concluded that all except 2 of 69 families had a posterior likelihood greater than 90% for linkage with 16p markers. In a study of 24 families with adult-onset polycystic kidney disease, Elles et al. (1990) found 2 families with unusual features consistent with a form unlinked to PKD1. Bachner et al. (1990) described a large 3-generation family with autosomal dominant polycystic kidney disease of clinically unusual form and no linkage to markers on the short arm of chromosome 16. Ultrasonographic screening of 60 family members identified 20 individuals, whose ages ranged from 10 to 80 years, with one or several cysts in only one kidney and 7 individuals with cysts in both kidneys. Others have pointed out that cysts may be unilateral in the early stages of ordinary polycystic kidney disease. Coto et al. (1992) found that 1 of 13 large Spanish families with autosomal dominant polycystic kidney disease did not show segregation with chromosome 16p markers. Bear et al. (1992) reported that in Newfoundland families in which the polycystic kidney disease did not cosegregate with chromosome 16 markers, the age of onset of end-stage renal disease was later (68.7 years) than in persons with chromosome 16-related disease (56.3 years). Ravine et al. (1992) analyzed 18 families (285 affected members) with mutations at the PKD1 locus and 5 families (49 affected persons) in which involvement at this locus was dismissed. Non-PKD1 patients lived longer than PKD1 patients (median survival, 71.5 vs 56.0 years, respectively), had a lower risk of progressing to renal failure, were less likely to have hypertension, were diagnosed at an older age, and had fewer renal cysts at the time of diagnosis. Although most of the PKD1 families were ascertained through clinics treating patients with renal impairment, no non-PKD1 family was identified through this source. Ravine et al. (1992) suggested that, partly because of the milder phenotype of APKD unlinked to chromosome 16, the reported prevalence of this genotype is probably an underestimate. Jeffery et al. (1993) also found milder progression of the disease ('less aggressive phenotype') in a Sicilian family with the form unlinked to chromosome 16. In 8 Spanish families with APKD, San Millan et al. (1995) confirmed earlier findings of a milder phenotype with PKD2. While the mean age of onset of end-stage renal disease was 54.2 +/- 8.1 years for PKD1, it was 66.2 +/- 3.3 years for PKD2. Coto et al. (1995) studied 17 large Spanish families with adult dominant polycystic kidney disease, 5 of which showed linkage to chromosome 4q (PKD2). They found that renal cysts developed at an earlier age in PKD1 mutation carriers, and end-stage renal failure occurred at an older age in people affected with PKD2. Hateboer et al. (1999) reported the results of a multicenter study of 333 persons with PKD1 (in 31 families), 291 persons with PKD2 (in 31 families), and 398 geographically matched controls. Median age at death or onset of end-stage renal disease was 53.0 years, 69.1 years, and 68.0 years for PKD1, PKD2, and controls, respectively. Women with PKD2 had a significantly longer median survival than men: 71.0 years versus 67.3 years, but no sex influence was apparent in PKD1. Age at presentation with kidney failure was later in PKD2 than in PKD1 (median age 74.0 vs. 54.3 years). PKD2 patients were less likely to have hypertension, a history of urinary tract infection, or hematuria. Deltas (2001) reviewed mutations in the PKD2 gene causing polycystic kidney disease. He repeated the observation that patients with PKD2 mutations run a milder course compared to PKD1 carriers, with an average 10 to 20 years later age of onset and lower probability to reach end-stage renal failure. Bergmann et al. (2008) reported a 4-generation family carrying a mutation in the PKD2 gene (173910.0009) with previously undetected disease, in which 2 fourth-generation sibs died in the perinatal period. The mother's first pregnancy resulted in a healthy girl; the second was complicated by oligohydramnios and massively enlarged hyperechogenic fetal kidneys, and the male infant born at 30 weeks' gestation died shortly after birth from respiratory failure. The third pregnancy was complicated from 20 weeks' gestation forward, and the infant girl born at 34 weeks' gestation also died shortly after birth; renal biopsy showed glomerulocystic kidney disease. Abdominal ultrasound examination revealed no cysts in the mother, but the father had 2 cortical cysts in the left kidney and 3 cysts in the right kidney, and the paternal grandmother and great-grandmother both had bilateral renal cysts. None of the adults had any clinical symptoms. Bataille et al. (2011) reported 3 unrelated probands with PKD2 and laterality defects, including situs inversus and dextrocardia; other members of these families with PKD2 did not have laterality defects. The findings suggested that laterality defects may occur in some patients with PKD2 mutations, as has been demonstrated in animal models (see, e.g., Pennekamp et al., 2002). Bataille et al. (2011) suggested that laterality defects may represent a qualitative difference between the PKD1 and PKD2 phenotypes.
Mochizuki et al. (1996) reported the isolation and characterization of a candidate gene for PKD2 on chromosome 4. They analyzed the PKD2 gene in affected individuals in 3 families with PKD2. Three nonsense mutations in the PKD2 gene ... Mochizuki et al. (1996) reported the isolation and characterization of a candidate gene for PKD2 on chromosome 4. They analyzed the PKD2 gene in affected individuals in 3 families with PKD2. Three nonsense mutations in the PKD2 gene were identified in affected individuals; see 173910.0001, 173910.0002, and 173910.0003. These mutations were not present in controls. Viribay et al. (1997) used heteroduplex and SSCP analyses in a systematic mutation screening of all 15 exons of the PKD2 gene in chromosome 4-linked ADPKD families, They identified and characterized 7 novel mutations, with a detection rate of approximately 90% in the populations studied. All of the mutations resulted in the premature stop of translation (e.g., 173910.0005). All the mutations were unique and were distributed throughout the gene without evidence of clustering. Comparison of specific mutations with a clinical profile in these families showed no clear correlation. Veldhuisen et al. (1997) systematically screened the PKD2 gene for mutations by SSCP analysis in 35 families with ADPKD and identified 20 mutations. Pei et al. (1998) screened for PKD2 mutations in 11 Canadian families with ADPKD. In 4 families, linkage to PKD2 had been documented; in the remaining 7 smaller families, one or more affected members had late-onset end-stage renal disease at age 70 or older, a feature suggesting PKD2. Pei et al. (1998) found mutations in 8 of the 11 families, with no difference in the detection rate between the PKD2-linked families and the families with late-onset ESRD. In 3 unrelated families, insertion or deletion of an adenosine in a polyadenosine tract, (A)8 at nucleotides 2152-2159, was found in exon 11, suggesting that this mononucleotide repeat tract is prone to mutations from 'slipped strand mispairing.' All the mutations, scattered between exons 1 and 11, were predicted to result in a truncated polycystin-2 that lacks both the calcium-binding EF-hand domain and the 2 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 mutations in the PKD2 coding sequence and disease severity. In both kidneys of a patient with PKD2, Koptides et al. (1999) identified, for the first time, multiple novel somatic mutations within the PKD2 gene of epithelial cells. The family involved in this case had previously been shown to possess a 1-bp insertion (173910.0004) as the germline mutation. In 7 (33%) of 21 cysts examined, the authors identified a different 1-bp insertion (173910.0007) within the inherited wildtype allele. In 2 other cysts, a nonsense mutation and a splice site deletion had occurred in a PKD2 allele that could not be identified as the inherited wildtype or mutant. Koptides et al. (1999) suggested that the autosomal dominant form of PKD2 occurs by a cellular recessive mechanism, supporting a 2-hit model for cyst formation. Koptides et al. (2000) provided the first direct genetic evidence that polycystins 1 and 2 interact, perhaps as part of a larger complex. In cystic DNA from a kidney of a patient with autosomal dominant PKD1, the authors showed somatic mutations not only in the PKD1 gene of certain cysts, but also in the PKD2 gene of others, generating a transheterozygous state with mutations in both genes. The mutation in PKD1 was of germinal nature and the mutation in PKD2 was of somatic nature. The authors stated that to their knowledge there was no precedent to the transheterozygous model as a mechanism for human disease development. Watnick et al. (2000) found somatic mutations of PKD2 in 71% of ADPKD2 cysts analyzed. They found clonal somatic mutations of PKD1 in a subset of cysts that lacked PKD2 mutations. In 10 cysts, they demonstrated that the wildtype PKD2 allele had acquired the mutation. They found 3 PKD2 cysts with somatic PKD1 mutations in each cyst; comprehensive screening of the entire PKD2 coding sequence was negative. They referred to this as a pathogenic effect of transheterozygous mutations. Torra et al. (1999) sought to demonstrate that somatic mutations are present in renal cysts from a PKD2 kidney. They studied 30 renal cysts from a patient with PKD2 in whom the germline mutation was shown to be a deletion that encompassed most of the gene. Loss of heterozygosity (LOH) studies showed loss of a wildtype allele in 10% of cysts. Screening of 6 exons of the gene by SSCP detected 8 different somatic mutations, all of which were expected to produce truncated proteins. Overall, more than 37% of the cysts studied represented somatic mutations. No LOH for the PKD1 gene or locus D3S1478 on chromosome 3 was observed in those cysts, which demonstrated that somatic alterations were specific. Pei et al. (2001) reported studies of an extensively affected Newfoundland family in which it appeared that there was bilineal disease from independently segregating PKD1 and PKD2 mutations. A PKD2 mutation (2152delA; L736X) was found in 12 affected pedigree members. In addition, when the disease status of these individuals was coded as unknown in linkage analysis, they found, with markers at the PKD1 locus, significant lod scores, i.e., greater than 3.0. The findings strongly supported the presence of a PKD1 mutation in 15 other affected pedigree members, who lacked the PKD2 mutation. Two additional affected individuals had transheterozygous mutations involving both genes, and they had renal disease that was more severe than that in affected individuals who had either mutation alone. This was said to be the first demonstration of bilineal disease in ADPKD. In humans, transheterozygous mutations involving both PKD1 and PKD2 are not necessarily embryonically lethal. The authors concluded that the presence of bilineal disease as a confounder needs to be considered in the search for the PKD3 locus. In affected members of 2 unrelated families with polycystic kidney disease, Bataille et al. (2011) identified 2 different heterozygous mutations in the PKD2 gene (173910.0010 and 173910.0011, respectively). In addition to kidney disease, the proband from each of the families also showed laterality defects, including situs inversus and dextrocardia, that were not seen in other affected family members. A third proband with PKD2 and a large 80-kb deletion involving PKD2 and ABCG2 (603756) also had laterality defects. The findings suggested that laterality defects may occur in some patients with PKD2 mutations, as has been demonstrated in animal models (see, e.g., Pennekamp et al., 2002).