De novomutations in the GTP/GDP-binding region of RALA, a RAS-like small GTPase, cause intellectual disability and developmental delay
Authors: Hiatt Susan M. , Neu Matthew B. , Ramaker Ryne C. , Hardigan Andrew A. , Prokop Jeremy W. , Hancarova Miroslava , Prchalova Darina , Havlovicova Marketa , Prchal Jan , Stranecky Viktor , Yim Dwight K.C. , Powis Zöe , Keren Boris , Nava Caroline , Mignot Cyril , Rio Marlene , Revah-Politi Anya , Hemati Parisa , Stong Nicholas , Iglesias Alejandro D. , Suchy Sharon F. , Willaert Rebecca , Wentzensen Ingrid M. , Wheeler Patricia G. , Brick Lauren , Kozenko Mariya , Hurst Anna C.E. , Wheless James W. , Lacassie Yves , Myers Richard M. , Barsh Gregory S. , Sedlacek Zdenek , Cooper Gregory M. 
Published: July 2018

Mutations that alter signaling of RAS/MAPK-family proteins give rise to a group of Mendelian diseases known as RASopathies, but 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, withde novoprotein-altering variation inRALA, 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 ofde novo RALAvariants in affected probands is significantly higher (p=4.93 × 10−11) than expected from the estimated mutation rate. Further, allde novovariants described here affect conserved residues within the GTP/GDP-binding region ofRALA; in fact, six alleles arose at only two codons, Val25 and Lys128. We directly assayed GTP hydrolysis and RALA effector-protein binding, and all but one tested variant significantly reduced both activities. 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 includeRALA, and provide additional insight into the pathogenesis of human disease caused by mutations in small GTPases.

Author Summary

While many causes of developmental disabilities have been identified, a large number of affected children cannot be diagnosed despite extensive medical testing. Previously unknown genetic factors are likely to be the culprits in many of these cases. Using DNA sequencing, and by sharing information among many doctors and researchers, we have identified a set of individuals with developmental problems who all have changes to the same gene,RALA.The affected individuals all have similar symptoms, including intellectual disability, speech delay (or no speech), and problems with motor skills like walking. In nearly all of these cases (10 of 11), the genetic change found in the child was not inherited from either parent. The locations and biological properties of these changes suggest that they are likely to disrupt the normal functions of RALA and cause significant health problems. We also performed experiments to show that the genetic changes found in these individuals alter two key functions of RALA. Together, we have provided evidence that genetic changes inRALAcan cause DD/ID. These results will allow doctors and researchers to identify additional children with the same condition, providing a clinical diagnosis to these families and leading to new research opportunities.