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Charcot-Marie-Tooth disease type 1a (CMT 1a) is an autosomal dominant peripheral neuropathy linked to the DNA markers D17S58 and D17S71, located in the pericentromeric region of the chromosome 17p arm. We analyzed an extended 5-generation Belgian family, multiply affected with CMT 1a, for linkage with eight chromosome 17 markers. The results indicated that the CMT 1a mutation is localized in the chromosomal region 17p11.2-p12 between the marker D17S71 and the gene for myosin heavy polypeptide 2 of adult skeletal muscle.

The alpha-spectrin locus (SPTA) on chromosome 1 maps to 1q22-q25 and alpha-spectrin specific probes detect restriction fragment length polymorphisms (RFLPs) with the endonucleases MspI and PvuII. The Duffy blood group (FY) has been mapped to the 1p21-q23 region. We found positive linkage between the alpha-spectrin and the Duffy loci with a maximal Lod score of 3.81 at theta = 0.0 using the computer program MLINK. This indicates that both loci are very closely linked and probably localized to 1q22-q23.

We report a large Belgian family with Charcot-Marie-Tooth disease (CMT) or hereditary motor and sensory neuropathy type I (HMSN-I). The pedigree consists of 5 generations with 350 family members comprising 42 patients. The disease is transmitted according to an autosomal dominant inheritance pattern. Several HMSN-I families have been reported to be closely linked to the Duffy blood group marker on chromosome 1. These families were designated HMSN-Ib families, opposed to the HMSN-Ia families which do not show evidence for such a linkage. Therefore we examined our family for the Duffy linkage relationship. We found no evidence for a strong linkage of the disease to the Duffy blood group locus, indicating that this family is of genetic subtype Ia.

We have recently demonstrated tight linkage of the Duffy blood group marker to the alpha-spectrin gene in an extended pedigree with Charcot-Marie-Tooth neuropathy. To determine a more precise location of the Duffy blood group locus on the chromosome 1 map we have tested several more chromosome 1 genes for linkage with this marker. We found suggestive linkage with the antithrombin III and apolipoprotein A2 genes and conclusive linkage with the gene coding for beta-nerve growth factor.

We previously reported a large Charcot-Marie-Tooth family not linked to the Duffy blood group marker, supporting the existence of genetic heterogeneity in this neuropathy. In order to investigate the possibility of another disease locus on chromosome 1, we analyzed this family further, using DNA polymorphisms of 6 genes. Absence of linkage makes a second disease locus on chromosome 1 unlikely.