Dominant mutations in the cation channel gene transient receptor potential vanilloid 4 cause an unusual spectrum of neuropathies

Abstract

Hereditary neuropathies form a heterogeneous group of disorders for which over 40 causal genes have been identified to date. Recently, dominant mutations in the transient receptor potential vanilloid 4 gene were found to be associated with three distinct neuromuscular phenotypes: hereditary motor and sensory neuropathy 2C, scapuloperoneal spinal muscular atrophy and congenital distal spinal muscular atrophy. Transient receptor potential vanilloid 4 encodes a cation channel previously implicated in several types of dominantly inherited bone dysplasia syndromes. We performed DNA sequencing of the coding regions of transient receptor potential vanilloid 4 in a cohort of 145 patients with various types of hereditary neuropathy and identified five different heterozygous missense mutations in eight unrelated families. One mutation arose de novo in an isolated patient, and the remainder segregated in families. Two of the mutations were recurrent in unrelated families. Four mutations in transient receptor potential vanilloid 4 targeted conserved arginine residues in the ankyrin repeat domain, which is believed to be important in protein-protein interactions. Striking phenotypic variability between and within families was observed. The majority of patients displayed a predominantly, or pure, motor neuropathy with axonal characteristics observed on electrophysiological testing. The age of onset varied widely, ranging from congenital to late adulthood onset. Various combinations of additional features were present in most patients including vocal fold paralysis, scapular weakness, contractures and hearing loss. We identified six asymptomatic mutation carriers, indicating reduced penetrance of the transient receptor potential vanilloid 4 defects. This finding is relatively unusual in the context of hereditary neuropathies and has important implications for diagnostic testing and genetic counselling.

Figure 1

Location of mutations in the different domains of TRPV4 protein. Neuropathy causing mutations are indicated as well as previously described mutations for autosomal-dominant brachyolmia, spondylometaphyseal dysplasia (SMDK), Kozlowski type and metatropic dysplasia. Mutations identified in this study are in bold. The new neuropathy associated mutations are indicated by asterisks.

Figure 2

Pedigrees of families with TRPV4 mutations. Segregation analysis and sequence trace files is shown for seven families, the pedigree of family F1 is shown elsewhere (Landoure et al., 2010). (A) Families CMT-455, CMT-456 and CMT-1100 carrying the Arg232Cys mutation. (B) Family CMT-858 with the Arg269Cys mutation. (C) Family CMT-165 with the Arg269His mutation. (D) Family CMT-149 with the Arg315Trp mutation. (E) Family PN-1394 with the Val620Ile mutation. Square = male; circle = female; black filled symbol = affected; empty symbol = unaffected; empty symbol with black dot = unaffected mutation carrier. Genotype is indicated under each individual from whom the DNA was available for testing.

Figure 3

The four mutations at arginine residues in the TRPV4 ARD localize to the same conserved, positively charged protein surface. (A) A ribbon representation of the structure of the TRPV4 ARD from chicken (Landoure et al., 2010), with a transparent molecular surface. The side chains of Arg232, Arg269 and Arg315 (Arg218, Arg255 and Arg301, respectively, in chicken) are shown in green ‘van der Waals’ sphere representation, and the previously identified Arg316 (Arg302 in chicken) (Deng et al., 2010) is shown in light green. The backbone positions of the skeletal dysplasia mutations at Ile331 and Asp333 (Krakow et al., 2009) are shown as yellow spheres for reference. (B) The sequence conservation in TRPV4, using an alignment of 27 TRPV4 orthologues, is mapped onto the surface of the structure. Note that Arg232, Arg269, Arg315 and Arg316 are strictly conserved as arginine residues in available TRPV4 orthologues. (C) The solvent-accessible electrostatic properties of the protein are mapped onto the molecular surface, with blue representing positively charged surfaces (+5 kT) and red, negatively charged surfaces (–5 kT). In (B) and (C) the surface regions corresponding to Arg232, Arg269, Arg315 and Arg316 are outlined in black.