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Context Familial pituitary diabetes insipidus has been described only in an autosomal dominant or recessive mode of inheritance. Objective This work aims to determine the cause of a novel form of familial diabetes insipidus (DI) that is controlled by desmopressin therapy but segregates in an X-linked recessive manner. Methods Thirteen members from 3 generations of the kindred with familial DI were studied. Water intake, urine volume, urine osmolality, plasma osmolality, and plasma vasopressin were measured under basal conditions, during fluid deprivation, 3% saline infusion, and water loading. Magnetic resonance images of the posterior pituitary also were obtained. In affected males, the effects of desmopressin therapy and linkage of the DI to markers for chromosome Xq28 were determined. In addition, the genes encoding vasopressin, aquaporin-2, the AVPR2 receptor, and its flanking regions were sequenced. Results This study showed that 4 males from 3 generations of the kindred have DI that is due to a deficiency of vasopressin, is corrected by standard doses of desmopressin, and segregates with markers for the AVPR2 gene in Xq28. However, no mutations were found in AVPR2 or its highly conserved flanking regions. Exome sequencing confirmed these findings and also revealed no deleterious variants in the provasopressin and aquaporin-2 genes. The 4 obligate female carriers osmo-regulated vasopressin in the low normal range. Conclusion X-linked recessive transmission of DI can be due to a defect in either the secretion or the action of vasopressin. Other criteria are necessary to differentiate and manage the 2 disorders correctly.

BACKGROUND: Spina bifida (SB) is the second most common nonlethal congenital malformation. The existence of monogenic SB mouse models and human monogenic syndromes with SB features indicate that human SB may be caused by monogenic genes. We hypothesized that whole exome sequencing (WES) allows identification of potential candidate genes by i) generating a list of 136 candidate genes for SB, and ii) by unbiased exome-wide analysis. METHODS: We generated a list of 136 potential candidate genes from three categories: and evaluated WES data of 50 unrelated SB cases for likely deleterious variants in 136 potential candidate genes, and for potential SB candidate genes exome-wide. RESULTS: We identified 6 likely deleterious variants in 6 of the 136 potential SB candidate genes in 6 of the 50 SB cases, whereof 4 genes were derived from mouse models, 1 gene was derived from human non-syndromic SB, and 1 gene was derived from candidate genes known to cause human syndromic SB. In addition, by unbiased exome-wide analysis, we identified 12 genes as potential candidates for SB. CONCLUSIONS: Identification of these 18 potential candidate genes in larger SB cohorts will help decide which ones can be considered as novel monogenic causes of human SB.

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most prevalent cause of chronic kidney disease that manifests in children. To date ~23 different monogenic causes have been implicated in isolated forms of human CAKUT, but the vast majority remains elusive. In a previous study, we identified a homozygous missense variant in E26 transformation-specific (ETS) Variant Transcription Factor 4 (ETV4) causing CAKUT via dysregulation of the transcriptional function of ETV4, and a resulting abrogation of GDNF/RET/ETV4 signaling pathway. This CAKUT family remains the only family with an ETV4 variant reported so far. Here, we describe one additional CAKUT family with a homozygous truncating variant in ETV4 (p. (Lys6*)) that was identified by exome sequencing. The variant was found in an individual with isolated CAKUT displaying posterior urethral valves and renal dysplasia. The newly identified stop variant conceptually truncates the ETS_PEA3_N and ETS domains that regulate DNA-binding transcription factor activity. The variant has never been reported homozygously in the gnomAD database. To our knowledge, we here report the first CAKUT family with a truncating variant in ETV4, potentially causing the isolated CAKUT phenotype observed in the affected individual.

Background: About 40 disease genes have been described to date for isolated congenital anomalies of the kidneys and urinary tract (CAKUT), the most common cause of childhood chronic kidney disease. However, these genes account for only 20% of cases. ARHGEF6, a guanine nucleotide exchange factor that is implicated in such biologic processes as cell migration and focal adhesion, acts downstream of integrin linked kinase (ILK) and parvin proteins. A genetic variant of ILK that causes murine renal agenesis abrogates the interaction of ILK with a murine focal adhesion protein encoded by Parva, leading to CAKUT in mice with this variant. Methods: To identify novel genes that, when mutated, result in CAKUT, we performed exome sequencing in an international cohort of 1265 families with CAKUT. We also assessed the effects in vitro of wild-type and mutant ARHGEF6 proteins, as well as the effects of Arhgef6 deficiency in mouse and frog models. Results: We detected six different hemizygous variants in the gene ARHGEF6 (which is located on the X chromosome in humans) in eight individuals from six families with CAKUT. In kidney cells, overexpression of wild-type ARHGEF6—but not proband-derived mutant ARHGEF6— increased active levels of CDC42/RAC1, induced lamellipodia formation, and stimulated PARVAdependent cell spreading. ARHGEF6 mutant proteins showed loss of interaction with PARVA. Three-dimensional MDCK cell cultures expressing ARHGEF6 mutant proteins exhibited reduced lumen formation and polarity defects. Arhgef6 deficiency in mouse and frog models recapitulated features of human CAKUT. Conclusions: Deleterious variants in ARHGEF6 may cause dysregulation of integrin-parvinRAC1/CDC42 signaling, thereby leading to X-linked CAKUT.

Pediatric steroid-sensitive nephrotic syndrome (pSSNS) is the most common childhood glomerular disease. Previous genome-wide association studies (GWAS) identified a risk locus in the HLA Class II region and three additional signals. But the genetic architecture of pSSNS, and its genetically driven pathobiology, is largely unknown. We conducted a multi-population GWAS meta-analysis in 38,463 participants (2,440 cases) and population specific GWAS, discovering twelve significant associations (eight novel). Fine-mapping implicated specific amino acid haplotypes in HLA-DQA1 and HLA-DQB1 driving the HLA Class II risk signal. Non-HLA loci colocalized with eQTLs of monocytes and numerous T-cell subsets in independent datasets. Colocalization with kidney eQTLs was lacking, but overlap with kidney cell open chromatin suggests an uncharacterized disease mechanism in kidney cells. A polygenic risk score (PRS) associated with earlier disease onset in two independent cohorts. Altogether, these discoveries expand our knowledge of pSSNS genetic architecture across populations and provide cellspecific insights into its molecular drivers.

Nephrolithiasis (NL) affects 1 in 11 individuals worldwide, leading to significant patient morbidity. NL is associated with nephrocalcinosis (NC), a risk factor for chronic kidney disease. Causative genetic variants are detected in 11-28% of NL and/or NC, suggesting additional NL/NC-associated genetic loci await discovery. Therefore, we employed genomic approaches to discover novel genetic forms of NL/NC.Exome sequencing and directed sequencing of the OXGR1 locus were performed in a worldwide NL/NC cohort. Putatively deleterious rare OXGR1 variants were functionally characterized.Exome sequencing revealed a heterozygous OXGR1 missense variant (c.371TG, p.L124R) co-segregating with calcium oxalate NL and/or NC disease in an autosomal dominant inheritance pattern within a multi-generational family with five affected individuals. OXGR1 encodes 2-oxoglutarate (α-ketoglutarate) receptor 1 in the distal nephron. In response to its ligand α-ketoglutarate (AKG), OXGR1 stimulates the chloride-bicarbonate exchanger Pendrin, which also regulates transepithelial calcium transport in cortical connecting tubules. Strong amino acid conservation in orthologues and paralogues, severe in silico prediction scores, and extreme rarity in exome population databases suggested the variant was deleterious. Interrogation of the OXGR1 locus in 1107 additional NL/NC families identified five additional deleterious dominant variants in five families with calcium oxalate NL/NC. Rare, potentially deleterious OXGR1 variants were enriched in NL/NC subjects relative to ExAC controls (ΧRare, dominant loss-of-function OXGR1 variants are associated with recurrent calcium oxalate NL/NC disease.

Congenital anomalies of the kidney and urinary tract (CAKUT) represent the most common cause of chronic kidney failure in children. Despite growing knowledge of the genetic causes of CAKUT, the majority of cases remain etiologically unsolved. Genetic alterations in roundabout guidance receptor 1 (ROBO1) have been associated with neuronal and cardiac developmental defects in living individuals. Although Slit-Robo signaling is pivotal for kidney development, diagnostic ROBO1 variants have not been reported in viable CAKUT to date. By next-generation-sequencing methods, we identified six unrelated individuals and two non-viable fetuses with biallelic truncating or combined missense and truncating variants in ROBO1. Kidney and genitourinary manifestation included unilateral or bilateral kidney agenesis, vesicoureteral junction obstruction, vesicoureteral reflux, posterior urethral valve, genital malformation, and increased kidney echogenicity. Further clinical characteristics were remarkably heterogeneous, including neurodevelopmental defects, intellectual impairment, cerebral malformations, eye anomalies, and cardiac defects. By in silico analysis, we determined the functional significance of identified missense variants and observed absence of kidney ROBO1 expression in both human and murine mutant tissues. While its expression in multiple tissues may explain heterogeneous organ involvement, variability of the kidney disease suggests gene dosage effects due to a combination of null alleles with mild hypomorphic alleles. Thus, comprehensive genetic analysis in CAKUT should include ROBO1 as a new cause of recessively inherited disease. Hence, in patients with already established ROBO1-associated cardiac or neuronal disorders, screening for kidney involvement is indicated.