Localization of PMP-22 gene (candidate gene for the Charcot-Marie-Tooth disease 1A) to band 17p11.2 by direct R-banding fluorescence in situ hybridization

Two Spanish families with Charcot-Marie-Tooth type 2A: clinical, electrophysiological and molecular findings

Mutations in the Mitofusin 2 (MFN2) gene have been related to the axonal type of Charcot-Marie-Tooth type 2 (CMT 2A). We report the first two Spanish families with CMT 2 and mutations in MFN2 gene. Molecular studies of one family with late onset revealed the novel mutation Arg364Gln. The affected family members presented mild clinical and electrophysiological worsening after 14 years of follow-up. The other family presented an early onset and optic atrophy. Molecular studies revealed the Arg94Gln mutation. This is the first report of a family in which this mutation is related to optic atrophy. Molecular analysis aimed at detecting mutations of MFN2 could be extremely useful in mild axonal neuropathies with slow evolution and indispensable in cases of dominant inheritance or optic atrophy. Population studies of mutations in MFN2 should be undertaken to discover the real frequencies in the Mediterranean area.

Molecular diagnosis of inheritable neuromuscular disorders. Part II: Application of genetic testing in neuromuscular disease

Molecular genetic advances have led to refinements in the classification of inherited neuromuscular disease, and to methods of molecular testing useful for diagnosis and management of selected patients. Testing should be performed as targeted studies, sometimes sequentially, but not as wasteful panels of multiple genetic tests performed simultaneously. Accurate diagnosis through molecular testing is available for the vast majority of patients with inherited neuropathies, resulting from mutations in three genes (PMP22, MPZ, and GJB1); the most common types of muscular dystrophies (Duchenne and Becker, facioscapulohumeral, and myotonic dystrophies); the inherited motor neuron disorders (spinal muscular atrophy, Kennedy's disease, and SOD1 related amyotrophic lateral sclerosis); and many other neuromuscular disorders. The role of potential multiple genetic influences on the development of acquired neuromuscular diseases is an increasingly active area of research.

Rapid Real-Time Fluorescent PCR Gene Dosage Test for the Diagnosis of DNA Duplications and Deletions

Background: Current methods to determine gene dosage are time-consuming and labor-intensive. We describe a new and rapid method to assess gene copy number for identification of DNA duplications or deletions occurring in Charcot-Marie-Tooth disease type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP), respectively.

Methods: We studied 16 patients with HNPP, 4 with CMT1A, and 49 control subjects. We used real-time PCR on the LightCycler system with use of a single capillary tube and no post-PCR handling. A polymorphic fragment of the PMP22 gene was amplified to determine gene dosage for heterozygous samples. The presence of two alleles was used to indicate that no deletion was present in HNPP samples. The ratio obtained between the areas under each allele melting curve of heterozygous CMT1A samples was used to determine whether the sequence was duplicated or normal. Homozygous samples required a competitive gene dosage test, where the ratio between the areas under the melting curves of the target DNA of samples and of the competitor molecule was used to determine whether the target sequence was duplicated, deleted, or normal. Samples from HNPP, CMT1A, and controls were analyzed.

Results: Area ratios were ∼0.6, 1.0, and 2.0 for HNPP, control, and CMT1A samples, respectively. The results agreed with those obtained by Southern blotting and microsatellite analysis in the same samples.

Conclusions: Direct and competitive real-time fluorescent PCR can differentiate one, two, or three copies of the target DNA. The method described is sensitive and accurate for detection of CMT1A duplications and HNPP deletions and is faster and easier than current methods.

Structure and function of peripheral nerve myelin proteins

(1) Two glycoproteins, P0 and PASII, are widely distributed in the peripheral myelin, but not in the central myelin of mammals. P0-like protein is expressed in both peripheral and central myelins of some lower vertebrates, such as fish and tadpoles. A close relationship is suggested between P0 expression and neural regenerative activity. (2) PMP22 was reported to show high sequence homology, not only to PASII, but also to the growth arrest specific protein. Human PASII/PMP22 sequence was deduced and the locus of its gene, chromosome 17p12-p11.2, is similar to the region linked to Charcot-Marie-Tooth disease type 1A. (3) P0 expressed on cultured cells mediated strong homophilic cell adhesion and neurite outgrowth. Addition of the P0 glycopeptide inhibited cell adhesion markedly, indicating that the oligosaccharide with peptide is essential for P0 mediated cell adhesion. The active site for neurite outgrowth in P0 appears to be different from the adhesion site. (4) We determined the human chromosomal locus of the P0 gene, 1q22-q23, which corresponded to the locus of hereditary motor and sensory neuropathy, Charcot-Marie-Tooth disease type 1B. Point mutations in the extracellular domain of P0 are found in the patient's chromosome. (5) L1 is a large multifunctional adhesive glycoprotein of 200 kD. Rat and human L1 sequences confirmed a common structure for the mammalian nervous systems. An isoform of L1 (L1cs), lacking four amino acids, appears to localize in non-neuronal cells such as Schwann cells, while the complete L1 is exclusively found in neurons. L1cs in Schwann cells may be functionally different from L1 in neurons.