Hereditary motor and sensory neuropathies (HMNS = Charcot-Marie-Tooth syndrom = CMT) and related neuropathies: Linkage analysis and gene identification in ulcero-mutilating neuropathies

Hereditary motor and sensory neuropathies (HMSN) are the most common inherited disorders of the peripheral nervous system with an incidence of 1 in 2500. Recent molecular genetic studies have shown heterogeneity of these disorders, dividing them into the subtypes HMSNIA-C, HMSNIIA-D, HMSNV, HMNII and V (hereditary motor neuropathy) and HSNI (hereditary sensory neuropathy) of autosomal dominant inheritance and X-linked forms. In contrast, HMSNIVA and B are inherited by an autosomal recessive trait. So far gene identification has only become available for the subtypes HMSNIA and B and X. The corresponding genes are the peripheral myelin protein (PMP22)-, the myelin protein zero (MPZ)-, and the connexin (Cx32)-gene, respectively. According to these genetically determined subtypes, clinical and neurophysiological examinations can differentiate corresponding phenotypes. Ulcero-mutilating neuropathies (i.e. genetically HMSNIIB and HSN) are characterised by typical clinical features like predominantly sensory loss and a varying degree of muscle weakness and wasting and frequent foot ulcers, which are complicated by osteolysis and/or osteomyelitis, not infrequently requiring amputations. In the last 2 years a series of patients with hereditary neuropathies have been investigated at the Department of Neurology in Graz. Neurological and electrophysiological examinations have been undertaken and DNA has been extracted. In Austria gene- identification has only been possible for patients with HMSNIA syndrome. DNA samples of patients and families with CMT caused by other mutations have been referred for gene identification or linkage analysis to Sydney (Australia) or Antwerp (Belgium), respectively. Study goals: 1. Clinical and electrophysiological examination of affected and unaffected persons, DNA and RNA isolation and establishment of lymphoblastoid cell lines from selected family members. 2. Mutation screening for affected persons. 3. Linkage analysis for known gene loci. 4. Whole genome scan. 5. Identification of the gene/genes of this novel form of ulcero-mutilating neuropathy. Persons and methods Affected and non affected members of 2 large families with ulcero-mutilating neuropathy have been clinically and electrophysiolocically investigated. After informed consent DNA has been extracted in all individuals. In one of the families the hitherto known gene loci on chromosome 3 and 9 have been excluded by linkage analysis

Using detailed neurological, electrophysiological and genetic methods in several families with hereditary neuropathies we have been able to narrow down the critical regions on human chromosomes that are responsible for expression of the disease. This is a very important step to find the gene or gene locus in the various families as the peripheral neuropathies are described as an extremely clinical and genetical heterogeneous disorder. It is also very important for the feasibility of a genetic counselling in the families. In collaboration with a Belgian working group we were able to improve the critical area for CMT2B and by analysing functional and positional candidate genes we have been able to find mutations in a gene in families from Austria, America and Scotland. In a large family from Austria we constructed a pedigree with more than 6 generations and we have been able to exclude all hitherto known genes and gene loci. We performed a whole genome scan using highly polymorphic DNA-markers distributed over the whole genome and could identify a new gene locus on the long arm of chromosome 11 in our family. At the moment we try to recruit new families with a similar phenotype to define the critical region more precisely. Furthermore we are annotating new genes through bioinformatics techniques and analyzing functional candidate genes for mutations in the coding region by direct DNA-sequencing.