Microcephaly is a devastating condition defined by a small head and small brain compared to the age- and sex-matched population. Mutations in a number of different genes causative for microcephaly have been identified, e.g., MCPH1, WDR62, and ASPM. Recently, mutations in the gene encoding the enzyme asparagine synthetase (ASNS) were associated to microcephaly and so far 24 different mutations in ASNS causing microcephaly have been described. In a family with two affected girls, we identified novel compound heterozygous variants in ASNS (c.1165G > C, p.E389Q and c.601delA, p.M201Wfs∗28). The first mutation (E389Q) is a missense mutation resulting in the replacement of a glutamate residue evolutionary conserved from Escherichia coli to Homo sapiens by glutamine. Protein modeling based on the known crystal structure of ASNS of E. coli predicted a destabilization of the protein by E389Q. The second mutation (p.M201Wfs∗28) results in a premature stop codon after amino acid 227, thereby truncating more than half of the protein. The novel variants expand the growing list of microcephaly causing mutations in ASNS.

Loss-of-function mutations of SLC34A3 represent an established cause of a distinct renal phosphate wasting disorder termed hereditary hypophosphatemic rickets with hypercalciuria (HHRH). SLC34A3 encodes the renal phosphate transporter NaPi2c expressed at the apical brush border of proximal renal tubules. Substitution of p.Ser192Leu is one of the most frequent genetic changes among HHRH patients in Europe, but has never been systematically evaluated, clinically or on a cellular level. Identification of a 32-year-old female with a homozgyous c.575C>T, p.Ser192Leu substitution enabled a more comprehensive assessment of the impact of this missense variant. Clinically, the patient showed renal phosphate wasting and nephrocalcinosis without any bone abnormalities. Heterozygous carriers of deleterious SLC34A3 variants were previously described to harbor an increased risk of kidney stone formation and renal calcification. We hence examined the frequency of p.Ser192Leu variants in our adult kidney stone cohort and compared the results to clinical findings of previously published cases of both mono- and biallelic p.Ser192Leu changes. On a cellular level, p.Ser192Leu-mutated transporters localize to the plasma membrane in different cellular systems, but lead to significantly reduced transport activity of inorganic phosphate upon overexpression in Xenopus oocytes. Despite the reduced function in ectopic cellular systems, the clinical consequences of p.Ser192Leu may appear relatively mild, at least in our index patient, and can potentially be missed in clinical practice.Electronic supplementary materialThe online version of this article (10.1007/s00240-019-01116-2) contains supplementary material, which is available to authorized users.

Kidney stone disease is an increasingly prevalent condition with remarkable clinical heterogeneity, with regards to stone composition, age of manifestation, rate of recurrence, and impairment of kidney function. Calcium-based kidney stones account for the vast majority of cases, but their etiology is poorly understood, notably their genetic drivers. As recent studies indicate, hereditary conditions are most likely underestimated in prevalence, and new disease genes are constantly being identified. As a consequence, there is an urgent need of a more efficient documentation and collection of cases with underlying hereditary conditions, to better understand shared phenotypic presentation and common molecular mechanisms. By implementation of a centralized patient registry on hereditary kidney stone disease in Germany, we aim to help closing the vast knowledge gap on genetics of kidney stone disease. In this context, clinical registries are indispensable for several reasons: first, delineating better phenotype–genotype associations will allow more precise patient stratification in future clinical research studies. Second, identifying new disease genes and new mechanisms will further reduce the rate of unknown nephrolithiasis/nephrocalcinosis etiology; and third, deciphering new molecular targets will pave the way to develop drugs for recurrence prevention in severely affected families.

Transforming growth factor β (TGF-β) signaling plays a fundamental role in metazoan development and tissue homeostasis. However, the molecular mechanisms concerning the ubiquitin-related dynamic regulation of TGF-β signaling are not thoroughly understood. Using a combination of proteomics and an siRNA screen, we identify pVHL as an E3 ligase for SMAD3 ubiquitination. We show that pVHL directly interacts with conserved lysine and proline residues in the MH2 domain of SMAD3, triggering degradation. As a result, the level of pVHL expression negatively correlates with the expression and activity of SMAD3 in cells, Drosophila wing, and patient tissues. In Drosophila, loss of pVHL leads to the up-regulation of TGF-β targets visible in a downward wing blade phenotype, which is rescued by inhibition of SMAD activity. Drosophila pVHL expression exhibited ectopic veinlets and reduced wing growth in a similar manner as upon loss of TGF-β/SMAD signaling. Thus, our study demonstrates a conserved role of pVHL in the regulation of TGF-β/SMAD3 signaling in human cells and Drosophila wing development.

Kidney stone disease (KSD) is a prevalent condition associated with high morbidity, frequent recurrence, and progression to chronic kidney disease (CKD). The etiology is multifactorial, depending on environmental and genetic factors. Although monogenic KSD is frequent in children, unbiased prevalence data of heritable forms in adults is scarce. Within 2 years of recruitment, all patients hospitalized for urological kidney stone intervention at our center were consecutively enrolled for targeted next generation sequencing (tNGS). Additionally, clinical and metabolic assessments were performed for genotype-phenotype analyses. The cohort comprised 155 (66%) males and 81 (34%) females, with a mean age at first stone of 47 years (4-86). The diagnostic yield of tNGS was 6.8% (16/236), with cystinuria (SLC3A1, SLC7A9), distal renal tubular acidosis (SLC4A1), and renal phosphate wasting (SLC34A1, SLC9A3R1) as underlying hereditary disorders. While metabolic syndrome traits were associated with late-onset KSD, hereditary KSD was associated with increased disease severity in terms of early-onset, frequent recurrence, mildly impaired kidney function, and common bilateral affection. By employing systematic genetic analysis to a less biased cohort of common adult kidney stone formers, we demonstrate its diagnostic value for establishing the underlying disorder in a distinct proportion. Factors determining pretest probability include age at first stone (<40 years), frequent recurrence, mild CKD, and bilateral KSD.