Phenotypic Spectrum of MFN2 Mutations in the Spanish Population

Carlos Casasnovas^1,*, Isabel Banchs², Julien Cassereau³, Naig Gueguen⁴, Arnaud Chevrollier⁴, Juan Antonio Martínez-Matos⁵, Dominique Bonneau⁴, Victor Volpini²

¹ Unitat de Neuromuscular. Hospital Universitari de Bellvitge - IDIBELL, Spain;
² Molecular Diagnostic Centre for Hereditary Diseases. Institut de Investigacions Biomèdiques d, Spain;
³ Departement de Neurologie, Centre Hospitalier Universitaire Angers, France;
⁴ Departement de Biochimie et Génétique, Centre Hospitalier Universitaire Angers, France;
⁵ Unitat de Neuromuscular. Hospital Universitari de Bellvitge, Spain

Correspondence to: Carlos Casasnovas, Unitat de Neuromuscular. Neurology Department, Hospital Universitari de Bellvitge - IDIBELL, Feixa Llarga s/n, L'Hospitalet de Llobregat, 08907, Spain; carloscasasnovas{at}bellvitgehospital.cat

Accepted 17 October 2009

The most common form of axonal Charcot–Marie–Tooth disease (CMT) is type 2A, caused by mutations in mitochondrial GTPase mitofusin 2 (MFN2). The objective of our study is to establish the incidence of MFN2 mutations in a cohort of Spanish patients with axonal CMT neuropathy. We studied 85 families with suspected axonal CMT. All MFN2 exons were studied through direct sequencing. A bioenergetics study in fibroblasts was conducted using a skin biopsy taken from a patient with an Arg468His mutation. Twenty-four patients from 14 different families were identified with nine different MFN2 mutations (Arg94Trp, Arg94Gln, Ile203Met, Asn252Lys, Gln276His, Gly296Arg, Met376Val, Arg364Gln, and Arg468His). All mutations were found in the heterozygous state and four of these mutations had not been described previously. MFN2 mutations were responsible for CMT2 in 16%±7.7% of the families studied and in 30.8%±14.2% (12/39) of families with known dominant inheritance. The bioenergetic studies in fibroblasts show typical results of MFN2 patients with a mitochondrial coupling defect (ATP/O) and an increase of the respiration rate linked to complex II. We conclude that mutations in MFN2 are the most frequent cause of CMT2 in this region. The Arg468His mutation was the most prevalent (6/14 families) and our study confirmed that it is pathological, presenting as a neuropathy in a mild to moderate degree. This study also demonstrated the value of MFN2 studies in cases of congenital axonal neuropathy, especially in cases of dominant inheritance, severe clinical symptoms, or additional symptoms such as optic atrophy.

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