We have investigated the peripheral myelin protein gene, PMP-22, in a family with Charcot-Marie-Tooth disease type 1A (CMT1A). The DNA duplication commonly found in CMT1A was absent in this family, but strong linkage existed between the disease and the CMT1A marker VAW409R3 on chromosome 17p11.2. We found a point mutation in PMP-22 which was completely linked with the disease. The mutation, a proline for leucine substitution in the first putative transmembrane domain, is identical to that recently found in the Trembler-J mouse. The presence of this PMP-22 defect in this CMT1A family and the location of PMP-22 within the DNA duplication associated with CMT1A suggest that both structural alteration and overexpression of PMP-22 may lead to the disease.

Charcot-Marie-Tooth disease type 1A (CMT1A) is associated with a DNA duplication at chromosome 17p11.2. In view of the point mutation in the gene for peripheral myelin protein pmp-22/gas-3 in Trembler mice, a murine model for CMT1A, we have analysed whether this gene is altered in CMT1A. Here we show that the human homologue of the murine pmp-22 gene is located within the CMT1A DNA duplication, which is a direct repeat and does not interrupt the coding region of PMP-22. Expression of PMP-22 in CMT1A fibroblasts is similar to expression in control fibroblasts. Increased gene dosage or altered PMP-22 expression in the peripheral nervous system are therefore possible mechanisms by which PMP-22 is involved in CMT1A.

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Mutations in the major peripheral myelin protein zero (PO) gene on chromosome Iq21-q23 have been found with the hereditary demyelinating polyneuropathy Char co t-Marie-Tooth type IB. Here, we describe 2 patients with distinct neurological characteristics, carrying differ ent substitutions at the saíne codon-Arg69His and Arg69Cys. The patients were heterozygous for the mutation3 which in both appeared to be de novo. Histological exam ination of sural nerve biopsy specimens revealed defective myelin as well as marked differences, confirming the im portance of PO in the compaction of myelin.

In this study, we describe the molecular cloning and characterization of a Src-like adaptor protein gene embedded within the genomic organization of the human thyroglobulin (Tg) gene. This gene was identified by exon trapping on overlapping cosmids encompassing the largest Tg intron. A 2.6-kb transcript, with the highest levels of expression in fetal brain and lung, was detected on Northern blots. Two full-length cDNAs (one alternatively spliced) were isolated from a fetal brain library, both containing an open reading frame of 276 amino acids, but lacking a catalytic tyrosine kinase domain. The gene shows a high degree of cross-species similarity and appears to be transcribed in the direction opposite to Tg. This gene, designated hslap, appears to be the human ortholog of the recently described gene for the murine Src-like adaptor protein (mSLAP), a candidate intermediate in the signal-transduction pathway of the Eck receptor tyrosine kinase. Human slap is located in the candidate region for a recessive demyelinating neuropathy on chromosome 8q24, but sequence analysis failed to identify mutations, suggesting that it is not the gene for this disease.Keywords : human Src-like adaptor protein; exon trapping ; intron ; thyroglobulin gene; chromosome 8.Little is known about the function of introns and very few BLAST [9] and GRAIL programs [10]. The search identified a novel Src-like adaptor protein (hSLAP) gene embedded in the examples are available of large human introns harbouring other genes, as is the case in the neurofibromatosis type 1 (NF1) and large conserved intron of the Tg gene. The hSLAP gene is abundantly expressed in fetal brain and in lung. Its murine counterblood clotting factor VIII (F8) genes [1, 2]. In this study, we have identified a novel gene located inside a large conserved part (mSLAP) has been shown to associate with the Eck receptor tyrosine kinase [11], a member of the Eph family of receptor intron of the thyroglobulin (Tg) gene. Tg is the glycoprotein precursor to the thyroid hormones. The Tg gene, assigned to protein tyrosine kinases (RPTKs) [12] thought to be involved in the development of the nervous system [13, 14]. In general, chromosome 8q24, spans 300 kb genomic DNA with a coding sequence spread over at least 37 exons and an 8.7-kb mRNA [3, RPTKs are involved in fundamental biological processes such as regulation of cell growth and differentiation [12]. Extracellular 4]. A large intron of 64 kb is located in the 3′ part of the gene [4]. The intron is conserved in various mammalian species and signals are transduced across the cellular membrane by these transmembrane receptors, which in this way become activated, is found in the same region in rat [5] and cow [6].enabling the phosphorylation of their cytoplasmic substrates. We have tested the possibility of evolutionary selection for Adaptor proteins, e.g. NCK, CRK and GRB2 [12], are a class this large intron, resulting from the presence of another gene of signaling molecules that lack a catalytic domain and bind to located with...

The most frequently found mutation in autosomal dominant hereditary motor and sensory neuropathy type I (HMSN I) is a large duplication on chromosome 17p11.2 containing probes VAW409R3, VAW412R3, and EW401. We investigated a family with severe features of HMSN I, and demonstrated the absence of this duplication by a quantitative analysis of the hybridization signals of VAW409R3 and VAW412R3. Linkage analysis, however, revealed linkage with probe VAW409R3a (lod score, 3.22), which demonstrates the existence of allelic heterogeneity within the HMSN Ia locus. These findings have implications for clinical practice and for investigating the identity of the HMSN Ia gene.

Zidovudine-induced mitochondrial myopathy in AIDS patients reported recently might be due to inhibition of mitochondrial DNA polymerase gamma. We investigated the effect of zidovudine on proliferation, differentiation, activity of mitochondrial- and nuclear-encoded enzymes, and mitochondrial DNA (mtDNA), in cultured human muscle cells. Marked inhibition of cell proliferation was found, even in the presence of low (10 mumol/L) zidovudine concentrations. Enzyme activity of the nuclear-encoded mitochondrial citrate synthase was not affected, and the partially mitochondrial-encoded cytochrome c oxidase was not decreased, except only after exposure to high concentrations (5 mmol/L) zidovudine. No decrease of mtDNA content and no mtDNA deletions were found in zidovudine-exposed muscle cells. We propose that the effect of zidovudine on muscle, seen in zidovudine-treated AIDS patients, results mainly from decrease in proliferation of muscle cells rather than inhibition of mtDNA replication.

Recently, it has been shown that Charcot-Marie-Tooth disease type 1a (CMT1a) is linked with a duplication of a DNA segment that is detected by probe VAW409R3, and that is located on chromosome 17p11.2. Here, we show that this duplication also contains VAW412R3a, but not A10-41 and EW503. Accounting for the duplication in recombination analysis, we found recombinants between CMT1a and EW301 and EW502, but not with A10-41, VAW409R3, and VAW412R3. Using pulsed-field gel electrophoresis analysis, we estimated the minimal size of the duplicated region in CMT1a patients to be 1100 kb.