Identification and in silico analysis of 14 novel GJB1, MPZ and PMP22 gene mutations

Abstract

Duplication within the chromosome 17p11.2 (CMT1Adup), peripheral myelin protein 22 (PMP22), myelin protein zero (MPZ) and gap junction b1-protein (GJB1) gene mutations are frequent causes of the CharcotMarie-Tooth disease (CMT). A large number of mutations in these genes are listed in databases. Sequence variants identified in patients are frequently reported as mutations without further evaluation. We analyzed 250 consecutively recruited unrelated Austrian CMT patients for CMT1Adup by microsatellite marker typing, real-time PCR or MLPA, and found 79 duplications (31.6%). The coding regions of the PMP22, MPZ and GJB1 genes were analyzed by direct sequencing in the remaining patients; 28 patients showed mutations, 14 of which were novel. We scored the pathogenicity of novel missense mutations by segregation studies and by their exclusion in control samples. Our comprehensive literature study found that up to 60% of the reported mutations in these genes had not been evaluated regarding their pathogenicity, and the PANTHER bioinformatics tool was used to score novel and published missense variants. The PANTHER program scored known polymorphisms as such, but scored B82-88% only of the published and novel mutations as most likely deleterious. Mutations associated with axonal CMT were less likely to be classified as deleterious, and the PMP22 S72L mutation repeatedly associated with severe CMT was classified as a polymorphism using default parameters. Our data suggest that this in silico analysis tool could be useful for assessing the functional impact of DNA variations only as a complementary approach. The CMT1Adup, GJB1, MPZ and PMP22 mutation frequencies were in the range of those described in other CMT patient collectives with different ethnical backgrounds.

Ferroportin disease: A systematic meta-analysis of clinical and molecular findings

“…We have assessed PolyPhen and SIFT [76] as alternatives to predict the effect of ferroportin mutations on protein function, because functional studies of ferroportin mutants [6,17,18,68,75] have shown conflicting results [17,18] . Our analysis shows that PolyPhen is a sensitive tool to identify disease-causing gene variants by classifying mutations identified in patients with iron overload as ‘possibly’ or ‘probably’ damaging.…”

Unusual Charcot–Marie–Tooth phenotype due to a mutation within the intracellular domain of myelin protein zero

“…Interestingly, this mutation reported as p.Asp195Tyr corresponds to the same position as in our patients (p.Asp234Tyr) after adapting the position after the MPZ reference sequence NM_000530. In addition, a familial case with the same mutation was recently reported,9 where disease onset in the index patient was found at 43 years of age with mild symptoms and a CMT1 phenotype. These findings indicate that this mutation can account for variable disease pathology phenotypes, including CMT1 or a mild CMT2, as indicated in our patients, as well as a variation in age at onset.…”

Neuropathy-related mutations alter the membrane binding properties of the human myelin protein P0 cytoplasmic tail

“…Functionally the most interesting mutant studied here is D224Y, which now has been described in at least 3 studies (Fabrizi et al 2006; Miltenberger-Miltenyi et al 2009; Schneider-Gold et al 2010). It is a gain-of-function mutant, inducing ordered lipid bilayer stacks in vitro , which are more tightly packed than those formed by wt-P0ct or the other variants.…”

“…Six known missense mutations are located within P0ct, of which four cause dominant demyelinating CMT type 1B (CMT1B). These include T216ER (Su et al 1993), D224Y (also referred to as D195Y and D234Y) (Fabrizi et al 2006; Miltenberger-Miltenyi et al 2009; Schneider-Gold et al 2010), R227S (Shy et al 2004), and the deletion of Lys236 (K236del) (Street et al 2002). In addition, K236E has been linked to dominant axonal CMT type 2I (CMT2I) (Choi et al 2004), and A221T, which was discovered as a co-mutation together with the deletion of Val42 in the Ig-like domain, was identified in a patient with DSS (Planté-Bordeneuve et al 2001).…”