Phenotypic variability in autosomal recessive axonal Charcot–Marie–Tooth disease due to the R298C mutation in lamin A/C

DOI: 10.1093/brain/awh021 Advanced Access publication November 7, 2003 Brain (2004), 127, 154±163 Phenotypic variability in autosomal recessive axonal Charcot±Marie±Tooth disease due to the R298C mutation in lamin A/C M. Tazir,1 H. Azzedine,4 S. Assami,1 P. Sindou,6 S. Nouioua,1 R. Zemmouri,1 T. Hamadouche,2 M. Chaouch,3 J. Feingold,4 J. M. Vallat,6 E. Leguern4,5 and D. Grid7 Summary Autosomal recessive forms of axonal Charcot±Marie± Tooth (ARCMT2) disease are frequent in some areas, such as North Africa and the Middle East, since consanguineous marriages are still common there. Recently, a unique homozygous mutation in LMNA, which encodes lamin A/C, a component of the nuclear envelope, was identi®ed in members of three Algerian families with ARCMT2 linked to chromosome 1q21.2-q21.3. In the present study we describe a group of 21 ARCMT2 patients from seven unrelated Algerian families with the same R298C mutation in the lamin A/C gene and marked variability of the clinical phenotype. There is a wide range of age of onset, from 6 to 27 years, with a mean of 14.4 6 4.6 years. The course of the disease varies considerably from one patient to another. Twelve patients with a disease duration of 10±15 years had a severe CMT phenotype with distal wasting and weakness of all four limbs and are¯exia associated with involvement of the proximal lower limb muscles. In Correspondence to: Pr M. Tazir, Service de Neurologie, CHU Mustapha 16.000 Algiers, Algeria E-mail: contrast, nine patients had the classical CMT phenotype with mild functional disability without proximal lower limb involvement after a disease duration of 5±18 years. Electrophysiological studies showed a median motor nerve conduction velocity (MNCV) in the normal range in almost all the patients. MNCV and compound muscle action potential (CMAP) values were inversely correlated with the disease duration and the MNCV was strictly related to the CMAP, strongly supporting a pure axonal process without a demyelinating component. Six patients had a nerve biopsy, which revealed severe rarefaction of myelinated ®bres in all cases and an increased density of unmyelinated ®bres in the majority of cases. In conclusion, the ARCMT2 associated with the R298C mutation differs from other types of ARCMT2. The variability among patients in the age of onset and the course of the disease strongly suggests the action of modifying genes, which remain to be identi®ed. Keywords: autosomal recessive CMT; lamin A/C gene mutation; phenotypic variability; modifying genes Abbreviations: ARCMT = autosomal recessive Charcot±Marie±Tooth; CMAP = compound muscle action potential; GDAP = ganglioside-induced differentiation-associated protein; MNCV = motor nerve conduction velocity Introduction Charcot±Marie±Tooth disease (CMT) or hereditary motor and sensory neuropathy (HMSN) represents a heterogeneous group of disorders which have been classi®ed according to clinical, electrophysiological, morphological and genetic criteria (Dyck and Lambert, 1968; Harding and Thomas 1980a; De Jonghe et al., 1998). Clinically, it is characterized by distal weakness and atrophy of the limb muscles, mild sensory loss and are¯exia. On the basis of motor nerve conduction velocity (MNCV) in the median nerve, the CMT disorders can be divided into Brain Vol. 127 No. 1 ã Guarantors of Brain 2003; all rights reserved 1Service de Neurologie, Centre Hospitalier Universitaire Mustapha, 2Laboratoire de Biologie Moleculaire, Institut Pasteur, 3Service de Neurologie, Centre Hospitalier Universitaire de Ben-Aknoun, Alger, Algeria, 4U 289 INSERM, 5De  partement de GeÂneÂtique, CytogeÂneÂtique et Embryologie, HoÃpital de la PitieÂ-SalpeÃtrieÁre, Paris, 6Centre Hospitalier Universitaire Dupuytren, Service de Neurologie, Limoges and 7Ge  neÂthon, Evry, France Phenotypic variability in ARCMT2A Patients and methods Clinical assessment Twenty-one patients from six families, their parents and most of their healthy siblings were assessed. All patients and the 41 at-risk relatives were examined for the presence of motor and sensory loss, are¯exia, foot deformities, scoliosis and other associated signs, such as nerve hypertrophy, tremor, ataxia, pyramidal signs and cranial nerve involvement. Disease severity was evaluated in terms of the ability to walk and run and to use the hands in daily tasks, according to the following scales. For the lower limbs, stage 0 = normal; 1 = normal walking and running but fatigability and cramps; 2 = normal walking, running and jumping impossible; 3 = abnormal walking without help; 4 = abnormal walking only with simple canes; 5 = abnormal walking, only with crutches; 6 = abnormal walking, only with a walker; 7 = wheelchair-bound; and 8 = bedridden. For the upper limbs, stage 0 = normal; 1 = mild disability with no effect on daily life; 2 = severe disability affecting daily life; 3 = claw hand; and 4 = no movements of ®ngers. Ophthalmological and auditory examination, cardiological ECG examination and echocardiography were performed on all the propositii and most of the secondary patients. All subjects gave informed consent to take part in the study which was approved by the Ministry of Health, Health Ethic Committee, Algeria. Electrophysiological analysis Nerve conduction studies were performed with surface stimulation and recording electrodes. MNCVs in the median and the peroneal nerves were recorded. Antidromic sensory compound action potential was recorded from the median and sural nerves. Electromyography of the tibialis anterior and the ®rst dorsalis interosseous muscle was performed with a concentric needle electrode. Pathological study Six patients from six families underwent super®cial peroneal nerve biopsy. For analysis of the nerve biopsy, fascicles of the super®cial peroneal nerves were divided into several pieces. One was ®xed in formaldehyde (10%) and embedded in paraf®n; routine sections were stained using conventional methods. Other fascicles were ®xed in buffered glutaraldehyde, processed and embedded in epon. Transverse semithin sections were stained with toluidine blue and ultrathin sections were stained with uranyl acetate and lead citrate and viewed in a Philips CM10 electron microscope. For technical reasons morphometric studies were performed only in ®ve cases. Genetic study Blood samples from the 41 individuals were obtained after informed consent. Genomic DNA was extracted using standard procedures. The R298C mutation was detected in the seven families with axonal ARCMT using restriction digestion by AciI of a polymerase chain reaction (PCR) fragment containing exon 5 of the lamin A/C gene. The mutation was con®rmed by sequencing the exon 5 of each index case after ampli®cation by PCR using previously published primers (De Sandre-Giovannoli, 2002). The 5¢3¢ and 3¢5¢ strands of the PCR products were sequenced with BigdyeÔ dRhodamine Terminatorsâ (PE Applied Biosystems) on an ABI 377 sequencer and sequence chro (...truncated)