De Novo Uroplakin IIIa Heterozygous Mutations Cause Human Renal Adysplasia Leading to Severe Kidney Failure

Abstract

Human renal adysplasia usually occurs sporadically, and bilateral disease is the most common cause of childhood end-stage renal failure, a condition that is lethal without intervention using dialysis or transplantation. De novo heterozygous mutations in Uroplakin IIIa (UPIIIa) are reported in four of 17 children with kidney failure caused by renal adysplasia in the absence of an overt urinary tract obstruction. One girl and one boy in unrelated kindreds had a missense mutation at a CpG dinucleotide in the cytoplasmic domain of UPIIIa (Pro273Leu), both of whom had severe vesicoureteric reflux, and the girl had persistent cloaca; two other patients had de novo mutations in the 3 UTR (963 T3 G; 1003 T3 C), and they had renal adysplasia in the absence of any other anomaly. The mutations were absent in all sets of parents and in siblings, none of whom had radiologic evidence of renal adysplasia, and mutations were absent in two panels of 192 ethnically matched control chromosomes. UPIIIa was expressed in nascent urothelia in ureter and renal pelvis of human embryos, and it is suggested that perturbed urothelial differentiation may generate human kidney malformations, perhaps by altering differentiation of adjacent smooth muscle cells such that the metanephros is exposed to a functional obstruction of urine flow. With advances in renal replacement therapy, children with renal failure, who would otherwise have died, are surviving to adulthood. Therefore, although the mechanisms of action of the UPIIIa mutations have yet to be determined, these findings have important implications regarding genetic counseling of affected individuals who reach reproductive age.

Mutational analyses of UPIIIA, SHH, EFNB2, and HNF1β in persistent cloaca and associated kidney malformations

“…All patients were 46 XX with normal gross karyotypes. Clinical summaries of the cases, including those of an individual (patient 6) with a known UPIIIA mutation (20), are shown in Table 1. Note that most had associated malformations of the upper renal tract and over half had impaired renal excretory function.…”

“…Polymerase chain reaction (PCR) amplification and sequencing of all exons plus 100-200 bp of surrounding sequence were performed for UPIIIA (six exons) and SHH (three exons) essentially as described by Jenkins et al (20); for SHH the primers used are those listed in Table 2 and 1× Buffer Q (Qiagen) was included in the reaction for PCR using primers SHH_3c since the 3' end of the gene is G:C rich. For HNF1β (nine exons) sequencing was performed as described (29).…”

“…An enzyme digest was designed to seek the specific mutation found in exon 6 of UPIIIA, a change in nucleotide 818 (C/T) leading to a Pro273Leu missense change (20). A 322-bp PCR product was generated using the HaeIII primers (Table 2).…”

“…Persistent cloaca has been associated with chromosome 7p rearrangements (18). Furthermore, mutations that disrupt a single gene can cause this malformation: homozygous mutations in the gene DHCR7 cause persistent cloaca in combination with renal aplasia/hypoplasia/ectopia as part of the Smith-Lemli-Opitz syndrome (19), and a heterozygous de-novo missense mutation in the cytoplasmic domain of UPIIIA (human chromosome 22q13.31), a gene expressed in the normal human embryonic urogenital sinus, was found in a girl who had persistent cloaca as well as renal adysplasia (20).…”

Genetics of vesicoureteral reflux

“…Mutations in UPK3A have recently been found in some patients with renal aplasia, hypoplasia and dysplasia, including some who had vur. 121,122 By contrast, other investigators found no evidence for major involvement of UPK3A in vur, [123][124][125][126] but concede that their results do not rule out mutations in regulatory elements affecting gene expression or function. 123,126 The X chromosome some strong candidate genes on the X chromosome (KAL1 and AGT2R) as well as reports of X-linked transmission and evidence suggesting linkage of primary vur to the pseudoautosomal region 22 led Kelly et al 125 to investigate the possibility of linkage in these areas in a study in 2009.…”