Whole-exome sequencing is a valuable diagnostic tool for inherited peripheral neuropathies: Outcomes from a cohort of 50 families.

The inherited peripheral neuropathies (IPNs) are characterized by marked clinical and genetic heterogeneity and include relatively frequent presentations such as Charcot-Marie-Tooth disease and hereditary motor neuropathy, as well as more rare conditions where peripheral neuropathy is associated with additional features. There are over 250 genes known to cause IPN-related disorders but it is estimated that in approximately 50% of affected individuals a molecular diagnosis is not achieved. In this study, we examine the diagnostic utility of whole-exome sequencing (WES) in a cohort of 50 families with 1 or more affected individuals with a molecularly undiagnosed IPN with or without additional features. Pathogenic or likely pathogenic variants in genes known to cause IPN were identified in 24% (12/50) of the families. A further 22% (11/50) of families carried sequence variants in IPN genes in which the significance remains unclear. An additional 12% (6/50) of families had variants in novel IPN candidate genes, 3 of which have been published thus far as novel discoveries (KIF1A, TBCK, and MCM3AP). This study highlights the use of WES in the molecular diagnostic approach of highly heterogeneous disorders, such as IPNs, places it in context of other published neuropathy cohorts, while further highlighting associated benefits for discovery.

Two females with mutations in USP9X highlight the variable expressivity of the intellectual disability syndrome.

The genetic causes of intellectual disability (ID) are heterogeneous and include both chromosomal and monogenic etiologies. The X-chromosome is known to contain many ID-related genes and males show a marked predominance for intellectual disability. Here we report two females with syndromic intellectual disability. The first individual was relatively mild in her presentation with mild-moderate intellectual disability, hydronephrosis and altered pigmentation along the lines of Blaschko without additional congenital anomalies. A second female presented shortly after birth with dysmorphic facial features, post-axial polydactyly and, on follow-up assessment, demonstrated moderate intellectual disability. Chromosomal studies for Individual 1 identified an X-chromosome deletion due to a de novo pericentric inversion; the inversion breakpoint was associated with deletion of the 5'UTR of the USP9X, a gene which has been implicated in a syndromic intellectual disability affecting females. The second individual had a de novo frameshift mutation detected by whole-exome sequencing that was predicted to be deleterious, NM_001039590.2 (USP9X): c.4104_4105del (p.(Arg1368Serfs*2)). Haploinsufficiency of USP9X in females has been associated with ID and congenital malformations that include heart defects, scoliosis, dental abnormalities, anal atresia, polydactyly, Dandy Walker malformation and hypoplastic corpus callosum. The extent of the congenital malformations observed in Individual 1 was less striking than Individual 2 and other individuals previously reported in the literature, and suggests that USP9X mutations in females can have a wider spectrum of presentation than previously appreciated.