Novel mutation in VCP gene causes atypical amyotrophic lateral sclerosis

Abstract

Objective: To identify the genetic variant that causes autosomal dominantly inherited motor neuron disease in a 4-generation Israeli-Arab family using genetic linkage and whole exome sequencing.

Methods: Genetic linkage analysis was performed in this family using Illumina single nucleotide polymorphism chips. Whole exome sequencing was then undertaken on DNA samples from 2 affected family members using an Illumina 2000 HiSeq platform in pursuit of potentially pathogenic genetic variants that comigrate with the disease in this pedigree. Variants meeting these criteria were then screened in all affected individuals.

Results: A novel mutation (p.R191G) in the valosin-containing protein (VCP) gene was identified in the index family. Direct sequencing of the VCP gene in a panel of DNA from 274 unrelated individuals with familial amyotrophic lateral sclerosis (FALS) revealed 5 additional mutations. Among them, 2 were previously identified in pedigrees with a constellation of inclusion body myopathy with Paget disease of the bone and frontotemporal dementia (IBMPFD) and in FALS, and 2 other mutations (p.R159C and p.R155C) in IBMPFD alone. We did not detect VCP gene mutations in DNA from 178 cases of sporadic amyotrophic lateral sclerosis.

Conclusions: We report a novel VCP mutation identified in an amyotrophic lateral sclerosis family (p.R191G) with atypical clinical features. In our experience, VCP mutations arise in approximately 1.5% of FALS cases. Our study supports the view that motor neuron disease is part of the clinical spectrum of VCP-associated disease.

Figure 1. Pedigree of valosin-containing protein (VCP) family FALS682

The arrow indicates the proband. Individuals III:2 and III:4 underwent full exome sequencing. Phenotype status is denoted by symbols as indicated. Individuals III:4 and III:9 had motor neuron disease, myopathy, and parkinsonism. Genders have been anonymized. FALS = familial amyotrophic lateral sclerosis.

Figure 2. Valosin-containing protein (VCP) mutations and crystal structure of VCP protein

(A) VCP mutations identified in inclusion body myopathy with Paget disease of the bone and frontotemporal dementia (IBMPFD) syndrome and amyotrophic lateral sclerosis (ALS): VCP mutations identified in individuals with the full IBMPFD syndrome are displayed in black. Mutations identified in this study in individuals with ALS (and other components of IBMPFD) are in red; those reported previously are in blue, whereas mutations detected both in the previous report and in the present study are in green. As illustrated, most of the mutations fall within the CDC48 polyubiquitin binding domain and the associated linker region L1 suggesting that these mutations interfere with the interaction of the VCP protein with polyubiquitinated substrates, and consequently with protein degradation by the proteasome. (B) Crystal structure of VCP protein showing the clustered locations of the mutated residues detected in familial ALS pedigrees in this study. The arginine at position 191 (implicated in the mutations p.R191G and in p.R191Q) is on a flexible loop corresponding to the linker between CDC48 and D1 domains (L1). The arginines at positions 155 and 159 (p.R155H and p.R159C) and the isoleucine at position 114 (p.I114V) are in β sheets within CDC48 domain. ADP = adenosine diphosphate; ATP = adenosine triphosphate; ATPase = adenosine triphosphatase.