L239F founder mutation in GDAP1 is associated with a mild Charcot-Marie-Tooth type 4C4 (CMT4C4) phenotype.

Over 40 mutations in the GDAP1 gene have been shown to segregate with Charcot-Marie-Tooth disease (CMT). Among these, only two mutations, i.e., S194X and Q163X have been reported in a sufficient number of CMT families to allow for the construction of reliable phenotype-genotype correlations. Both the S194X and Q163X mutations have been shown to segregate with an early-onset and severe neuropathy resulting in loss of ambulance at the beginning of the second decade of life. In this study, we identified the L239F mutation in the GDAP1 gene in one Bulgarian and five Polish families. We hypothesized that the L239F mutation may result from a founder effect in the European population since this mutation has previously been reported in Belgian, Czech, and Polish patients. In fact, we detected a common disease-associated haplotype within the 8q13-q21 region in the Polish, German, Italian, Czech, and Bulgarian CMT families. Like the previously detected "regional" S194X and Q163X mutations, respectively present in Maghreb countries and in patients of Spanish descent, the L239F mutation seems to be the most common GDAP1 pathogenic variant in the Central and Eastern European population. Given the likely presence of a common ancestor harboring the L239F mutation, we decided to compare the phenotypes of the CMT (L239F) patients collected in this study with those of previously reported cases. In contrast to CMT4A caused by the S194X and Q163X mutations, the CMT phenotype resulting from the L239F substitution represents a milder clinical entity with a long-preserved period of ambulance at least until the end of the second decade of life.

Emery-Dreifuss muscular dystrophy: a novel mutation in the LMNA gene.

Described here is the phenotypical expression of a novel LMNA mutation c.1157 G>T in a Czech patient with an early-onset form of Emery-Dreifuss muscular dystrophy. The mutation predicts aberrant splicing. Now 21 years old, the patient has had slowly progressing muscle dystrophy since the age of one and early contractures of elbows. He is the only family member affected. Even though the dystrophy typically affects the heart as well, in the present case these signs are not yet expressed.

Mutations in the LMNA gene do not cause axonal CMT in Czech patients.

The LMNA gene was sequenced in 98 Czech patients from 94 unrelated families with early-onset axonal Charcot-Marie-Tooth (CMT) disease consistent with both autosomal recessive inheritance and sporadic cases. Biallelic pathogenic mutations were not found in any patient in this group. One patient carried the c.1870C>T mutation that is predicted to result in the amino-acid substitution, p. Arg624Cys, on one allele, but the second causative mutation was not detected. LMNA mutation is not likely to be associated with the disease in this family. To exclude larger deletions/duplications in the LMNA gene not detectable by sequencing, 48 patients from this group were also analyzed with multiplex ligation-dependent probe amplification. No rearrangements in the LMNA gene were detected. We conclude that mutations in the LMNA gene are absent from a large group of Czech patients with axonal autosomal recessive CMT disease. Consequently, LMNA mutation screening does not seem to be relevant for axonal CMT DNA diagnostics. A similar situation may apply to other European populations.

Quantitative multiplex real-time PCR for detection of PLP1 gene duplications in Pelizaeus-Merzbacher patients.

Pelizaeus-Merzbacher disease (PMD) is an X-linked recessive disorder of central nervous system (CNS) myelination typically affecting males. A genomic duplication of variable size at Xq22.2, containing the entire proteolipid protein 1 gene (PLP1), is responsible for approximately 60-70% of PMD cases. The aim of this study was to develop a rapid and robust method for determination of PLP1 gene dosage. We optimized two multiplex real-time quantitative PCR (Q-PCR) assays targeting exons 3 and 6 of the PLP1 gene, and then validated these assays by retrospective analysis of a set of genomic DNAs from 67 previously tested patients and 43 normal controls. Samples were analyzed in multiplex PCR reactions using TaqMan chemistry and the ABI Prism 7000 Sequence Detection System. PLP1 dosage was determined by the relative quantitative comparative threshold cycle method (DeltaDeltaCt) using the human serum albumin gene as the endogenous reference gene. Three clearly non-overlapping ranges of results, corresponding to the presence of one, two, or three PLP1 copies, were detected in both assays. The results were completely concordant with gender and previous PLP1 gene dosage testing based on quantitative fluorescent multiplex PCR and analysis of a dinucleotide polymorphism in the first intron of the PLP1 gene. We conclude that multiplex real-time Q-PCR represents a fast and reliable tool for PLP1 duplication testing in PMD families.