De novo mutations in the GTP/GDP-binding region of RALA, a RAS-like small GTPase, cause intellectual disability and developmental delay.

Mutations that alter signaling of RAS/MAPK-family proteins give rise to a group of Mendelian diseases known as RASopathies. However, among RASopathies, the matrix of genotype-phenotype relationships is still incomplete, in part because there are many RAS-related proteins and in part because the phenotypic consequences may be variable and/or pleiotropic. Here, we describe a cohort of ten cases, drawn from six clinical sites and over 16,000 sequenced probands, with de novo protein-altering variation in RALA, a RAS-like small GTPase. All probands present with speech and motor delays, and most have intellectual disability, low weight, short stature, and facial dysmorphism. The observed rate of de novo RALA variants in affected probands is significantly higher (p = 4.93 x 10(-11)) than expected from the estimated random mutation rate. Further, all de novo variants described here affect residues within the GTP/GDP-binding region of RALA; in fact, six alleles arose at only two codons, Val25 and Lys128. The affected residues are highly conserved across both RAL- and RAS-family genes, are devoid of variation in large human population datasets, and several are homologous to positions at which disease-associated variants have been observed in other GTPase genes. We directly assayed GTP hydrolysis and RALA effector-protein binding of the observed variants, and found that all but one tested variant significantly reduced both activities compared to wild-type. The one exception, S157A, reduced GTP hydrolysis but significantly increased RALA-effector binding, an observation similar to that seen for oncogenic RAS variants. These results show the power of data sharing for the interpretation and analysis of rare variation, expand the spectrum of molecular causes of developmental disability to include RALA, and provide additional insight into the pathogenesis of human disease caused by mutations in small GTPases.

A novel CLCN5 mutation in a boy with asymptomatic proteinuria and focal global glomerulosclerosis.

Dent disease is an X-linked proximal tubulopathy that typically presents with hypercalciuria, low-molecular-weight proteinuria and slow progression to endstage renal disease. We report the case of a 5-year-old boy who presented with asymptomatic nephrotic range proteinuria and was later diagnosed with Dent disease. Absence of specific glomerular pathology in the first kidney biopsy led to erroneous treatment for presumably unsampled primary focal segmental glomerulosclerosis. Aggressive angiotensin blockade and immunosuppression resulted in significant side effects with marginal benefit. The continued nonspecific findings after a second kidney biopsy 2 years later led to the suspicion of a congenital tubulopathy. We detected a novel CLCN5 gene mutation, c.1396G > C, that creates a G466R missense change in the ClC-5 protein. Dent disease should be considered in the differential diagnosis of asymptomatic proteinuria for male patients. Profiling proteinuria in these patients by spot urine albumin/creatinine ratio may give the first clue to a tubulopathy. Determining the extent to which the clinical work-up should proceed for females with Dent phenotype or asymptomatic proteinuria remains to be a challenging clinical dilemma.

Sertoli cell vacuolization and abnormal germ cell adhesion in mice deficient in an inositol polyphosphate 5-phosphatase.

The dynamic nature of cellular interactions during differentiation of germ cells and their translocation from the basement membrane to the lumen of the seminiferous tubules requires the existence of complex and well-regulated cellular adhesion mechanisms in the testis. Successful migration of the developing germ cells is characterized by dynamic breakage and reformation of cadherin-containing adherens junctions between the germ cells and Sertoli cells, the polarized somatic cells of the testis that support and nourish the developing gametes. Here, we demonstrate the accumulation of abnormally swollen, actin-coated, endosome-like structures that contain intact adherens junctions and stain positive for N-cadherin and beta-catenin in the Sertoli cell cytosol of mice deficient in Inpp5b, an inositol polyphosphate 5-phosphatase. Simultaneous to the formation of these abnormal structures, developing germ cells are prematurely released from the seminiferous epithelium and sloughed into the epididymis. Our results demonstrate a role for Inpp5b in the regulation of cell adhesion in the testis and in the formation of junctional complexes with neighboring cells, and they emphasize the important and essential role of phosphoinositides in spermatogenesis.