Patients homozygous for the 17p 11.2 duplication in charcot-marie-tooth type 1A Disease

Charcot-Marie-Tooth type 1A disease is an inherited sensorimotor neuropathy that is most often associated with a duplication of chromosome 17p11.2. This region contains the gene of the peripheral myelin protein 22 (PMP22), which is responsible by a gene dosage effect for the Charcot-Marie-Tooth type 1A phenotype with 17p11.2 duplication. We performed a clinical, electrophysiological, and genetic study of a consanguinous Charcot-marie-Tooth type 1A family with 4 affected siblings, 3 of whom were homozygous for the 17p11.2 duplication, the other a heterozygote. Comparison of phenotypes showed that the severity of the disease was more severely affected than the heterozygous sibling who was pausiymptomatic. These results suggest that the severity of the disease is not determined solely by the number of copies of the PMP22 gene.     

Immunology

A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in immunology.     

The kinesin superfamily protein Rab6KIFL is not involved in the pathophysiology of Charcot-Marie-Tooth disease type 4C

Charcot-Marie-Tooth disease type 4C (CMT4C) is an autosomal recessive peripheral neuropathy reported in several Algerian families. The gene locus of this disease has been narrowed to 5q31-33. Recently, a missense mutation in the gene for the kinesin superfamily KIF1B was reported as the cause of Charcot Marie Tooth disease type 2A (CMT2A). We suspected that Rab6KIFL, one of the kinesin superfamily proteins, might be involved in the pathophysiology of CMT4C, because Rab6KIFL gene is located in 5q31. The coding regions of the Rab6KIFL gene of genomic DNA derived from one Algerian family with CMT4C were analyzed by direct sequencing. No mutation in Rab6KIFL gene was found in this family. Further investigation is necessary to identify the causative gene for CMT4C.     

Rapid detection of 17p11.2 rearrangements by FISH without cell culture (direct FISH,DFISH): a prospective study of 130 patients with inherited peripheral neuropathies

Charcot-Marie-Tooth (CMT) disease and hereditary neuropathy with pressure palsies (HNPP) are two frequent hereditary motor and sensory neuropathies. CMT is characterized by slowly progressive weakness and atrophy, primarily in peroneal and distal leg muscles. The most frequent form, CMT1A, is due, in most cases, to the duplication of a 1.5 Mb region on chromosome 17p11.2 containing the peripheral myelin protein 22 gene (PMP22). The phenotype seems to result from dosage of the PMP22 gene. This hypothesis is reinforced by the existence of HNPP, which is clinically characterized by various recurrent truncular palsies or sensory loss precipitated by minor trauma, which is caused by deletion of the same 1.5 Mb region in 17p11.2. In clinical practice, the detection of the duplication or the deletion in 17p11.2, which permits a positive diagnosis, is still performed by time consuming methods (Southern blot or various combinations of molecular tools). We developed a method for the rapid detection of 17p11.2 rearrangements, using "direct FISH" and PRINS analyses, which does not require cell culture. In a prospective study of 92 patients with CMT and 38 with suspected HNPP, we compared this new technique to classical strategies like Southern blot. The results demonstrate the high sensitivity and specificity of the new FISH technique for the diagnosis of CMT1A and HNPP. Moreover, because of its simplicity and rapidity, this technique provides a useful alternative to the molecular approaches that have been used to diagnose segmental aneusomies, especially in the case of duplications that often go undetected.     

A de novo case of hereditary neuropathy with liability to pressure palsies (HNPP) of maternal origin: a new mechanism for deletion in 17p11.2?

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant neuropathy, most often associated with a deletion of the 17p11.2 region, which is duplicated in 70% of patients with Charcot- Marie-Tooth type 1 (CMT1A). Most de novo CMT1A and HNPP cases have been of paternal origin. A rare case of de novo HNPP of maternal origin was analysed to determine the underlying mechanism. Affected individuals in the family carried a deletion corresponding to the CMT1A/HNPP monomer unit associated with a rearrangement of the CMT1A-REP sequences. Segregation analysis of 17p11-p12 markers in the family indicated that the deletion was not generated by unequal crossing over between homologous 17 chromosomes, as in de novo cases from paternal origin, but rather by an intrachromosomal rearrangement. Two distinct mechanisms can therefore lead to the same 17p11.2 deletion. This result suggests that intrachromosomal rearrangement may be specific to maternal transmissions.      

Expression of xenogeneic MHC class II molecules in HLA-DR(+) and -DR(-) cells: influence of retrovirus vector design and cellular context

We recently established that molecular chimeras of major histocompatibility complex (MHC) class II molecules, created via retroviral transfer of allogeneic class II cDNAs into bone marrow cells (BMCs), alleviated complications associated with mixed BMC chimeras while leading to T cell tolerance to renal grafts sharing the transferred class II. Initially demonstrated for allogeneic transplants in miniature swine, this concept was extended to T-dependent antibody (Ab) responses to xenogeneic antigens (Ags) in the pig --> baboon combination. Successful down-regulation of T cell responses appeared, however, to be contingent on a tight lineage-specific expression of transferred class II molecules. The present studies were, therefore, designed to evaluate the influence of construct design and cellular environment on expression of retrovirally transferred xenogeneic class II cDNAs. Proviral genomes for pig class II SLA-DR expression, differing only at the marker neo(r) or enhanced green fluorescent protein (EGFP) gene, showed increased membrane SLA-DR density on HLA-DR(-) fibroblasts as well as HLA-DR(+), TF-1 erythroleukemia cells. More importantly, HLA-DR(+) human B cell lines, although efficiently transduced with pig DR retroviruses, exhibited unstable surface pig DR. Surface pig DR- B cells, nevertheless, stimulated autologous human T cells pre-sensitized to pig Ags, a proliferation likely occurring through presentation of class II-derived peptides. Collectively, these data suggest that surface expression of transferred class II molecules is not related to the ability of recipient cells to synthesize xenogeneic class II molecules but rather to their Ag processing capacities.     

Coincidence of two genetic forms of Charcot-Marie-Tooth disease in a single family

The authors report a family in which two affected first cousins had a severe demyelinating Charcot-Marie-Tooth disease (CMT) phenotype. One had related parents, and there were no other affected relatives, suggesting an autosomal recessive mode of inheritance. Molecular studies showed that a de novo duplication in 17p11.2 and a second mutation in MTMR2 were present.