Renal Hypodysplasia/aplasia 3

A number sign (#) is used with this entry because of evidence that renal hypodysplasia/aplasia-3 (RHDA3) is caused by heterozygous mutation in the GREB1L gene (617782) on chromosome 18q11.

Description

RHDA3 is an autosomal dominant disorder characterized by abnormal kidney development beginning in utero. The phenotype is highly variable, even within families, and there is evidence for incomplete penetrance. Some affected individuals have bilateral renal agenesis, which is usually fatal in utero or in the perinatal period, whereas others may have unilateral agenesis that is compatible with life, or milder manifestations, such as vesicoureteral reflux (VUR). Female mutation carriers may also have uterine or ovarian abnormalities. Renal aplasia falls at the most severe end of the spectrum of congenital anomalies of the kidney and urinary tract (CAKUT; see 610805) (summary by Brophy et al., 2017 and Sanna-Cherchi et al., 2017).

For a discussion of genetic heterogeneity of renal hypodysplasia/aplasia, see RHDA1 (191830).

Clinical Features

Brophy et al. (2017) reported 2 unrelated families with RHDA3. Family 1 was from Iowa in the United States and family 2 was Danish. Affected individuals in both families had unilateral or bilateral renal agenesis; family 2 had 2 affected fetuses, and the pregnancies were terminated.

Sanna-Cherchi et al. (2017) reported 17 probands with various manifestations of renal hypodysplasia/aplasia. The patients had unilateral renal dysplasia, renal aplasia, and/or multicystic kidneys. One patient (DC13) had bilateral renal agenesis, bladder agenesis, and Potter sequence. His sister had vesicoureteral reflux and his mother had an anomaly of the uterus. Another patient (AC6) had bilateral renal dysplasia and congenital hydronephrosis; her 2 first cousins reportedly had vesicoureteral reflux. One patient (DC9) had renal agenesis, unicornuate uterus, and agenesis of the left ovary. Eight patients had a family history of the disorder, although clinical details were limited.

De Tomasi et al. (2017) reported 16 unrelated families with RHDA3. The phenotype was highly variable: 14 families contained affected fetuses with bilateral kidney agenesis that died in utero or whose pregnancies were terminated due to the condition. Other living mutation carriers had variable urogenital abnormalities, including unilateral kidney agenesis, vesicoureteral reflux, horseshoe kidney, and unicornuate uterus; multicystic dysplasia was rarely observed. There were several asymptomatic mutation carriers, indicating incomplete penetrance. Some patients had additional manifestations, most often preauricular ear tags and rib abnormalities.

Inheritance

The transmission pattern of RHDA3 in the families reported by Brophy et al. (2017), Sanna-Cherchi et al. (2017), and De Tomasi et al. (2017) was consistent with autosomal dominant inheritance with incomplete penetrance. De Tomasi et al. (2017) observed a maternal transmission bias.

Molecular Genetics

In affected members of 2 unrelated families with RHDA3, Brophy et al. (2017) identified heterozygous mutations in the GREB1L gene (617782.0001 and 617782.0002). The mutations, which were found by whole-exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the families, but showed incomplete penetrance. One mutation was a frameshift, predicted to result in a loss of function and haploinsufficiency; the other mutation was a missense variant, and functional studies of that variant were not performed.

In 17 probands with RHDA3, Sanna-Cherchi et al. (2017) identified heterozygous mutations in the GREB1L gene (see, e.g., 617782.0003-617782.0007). The first 9 mutations were found by whole-exome sequencing of 202 individuals with the disorder and were confirmed by Sanger sequencing. Subsequent direct screening of the GREB1L gene in a further 410 cases identified 8 additional heterozygous mutations in 8 probands. There were 4 loss-of-function mutations and 13 missense variants. Among the 17 variants, 1 was proven de novo, 1 was shared with an affected sister and mother, 1 was shared with an affected sister, 2 were inherited from an affected parent, and 4 were inherited from an apparently unaffected parent. Parental DNA from 8 other probands was unavailable. Overall, 17 (2.8%) of 604 patients with RHDA carried heterozygous GREB1L mutations. These data strongly implicated dominant mutations in GREB1L as a cause of the disorder; statistical analysis based on exome-wide collapsing analysis with segregation and de novo occurrence yielded a highly significant combined p value of 2.3 x 10 (-7). Studies of patient cells were not performed, but the presence of 4 nonsense or frameshift mutations suggested haploinsufficiency as the pathogenetic mechanism. Expression of 4 of the human missense mutations in mutant zebrafish with morpholino knockdown of the greb1l ortholog failed to rescue the disrupted renal phenotype, suggesting that these missense mutations result in a loss of function.

In affected members of 16 unrelated families with RHDA3, De Tomasi et al. (2017) identified 16 different heterozygous mutations in the GREB1L gene (see, e.g., 617782.0008-617782.0013). The mutations in the first 2 families were found by whole-exome sequencing of 15 affected families. Mutations in the subsequent 14 families were found by targeted sequencing of 168 additional probands with a similar disorder. Overall, there were 12 missense mutations, 3 frameshift mutations, and 1 splice site mutation. Twelve of the variants were absent from the gnomAD database, whereas 2 of the missense variants were found at very low frequencies in that database. In 11 of the 12 families with available parental DNA, the variant was inherited from the mothers, most of whom had kidney or uterine anomalies. However, several mothers and 2 children with a variant were unaffected, indicating incomplete penetrance. De Tomasi et al. (2017) noted an observed maternal bias in transmission and postulated that either imprinting or adverse effects on male fertility may be responsible. In their cohort, 12 (25.8%) of 54 cases with bilateral kidney agenesis carried a variant in the GREB1L gene.

Animal Model

In zebrafish embryos, Brophy et al. (2017) found expression of the greb1l gene in the pronephros portion of the intermediate mesoderm that gives rise to the pronephros very early in the developing kidney. The authors reported an N-ethyl-N-nitrosourea-induced mutation in the zebrafish Greb1l gene that caused a premature stop codon at amino acid 1915. The mutation resulted in periorbital edema, pericardial effusion, and cystic kidneys at day 3 postfertilization. Morpholino- or CRISPR/Cas9-mediated targeting of Greb1l resulted in similar phenotypes. CRISPR/Cas9-generated Greb1l mouse mutants showed exencephaly, unilateral or bilateral cleft lip, and unilateral or bilateral kidney defects, including agenesis.

Sanna-Cherchi et al. (2017) found expression of Greb1l in the developing murine kidney, ureter, and bladder. Morpholino knockdown and CRISPR/Cas9 genome editing of the greb1l ortholog in zebrafish embryos resulted in a progressive dose-dependent reduction in the area of the proximal renal convoluted tubule. These defects could be rescued by expression of wildtype human GREB1L.

De Tomasi et al. (2017) failed to obtain homozygous Greb1l-knockout pups generated by CRISPR/Cas9 technology. At embryonic day 13.5, Greb1l -/- embryos showed exencephaly and were significantly smaller than Greb1l +/- or wildtype embryos. All Greb1l -/- embryos lacked kidneys and showed cardiac morphogenesis defects, with both ventricles on the left side. Furthermore, all male and female Greb1l -/- embryos lacked wolffian and mullerian ducts, respectively.