Evidence for genetic heterogeneity underlying hereditary neuropathy with liability to pressure palsies.

Hereditary neuropathy with liability to pressure palsies (HNPP) is a disorder of the peripheral nervous system, the cause of which has recently been identified as a deletion on chromosome 17p. The deletion corresponds to the duplication that is commonly observed in patients with hereditary motor and sensory neuropathy type Ia (HMSNIa, 17p11.2-p12). Therefore, the gene for peripheral myelin protein 22 (PMP-22) is a candidate gene for both HMSNIa and HNPP. Here, we show that a similar deletion is present in one family with HNPP but is clearly absent in another family. Affected members of this family carry the expected two copies of the PMP-22 gene and the surrounding region. Furthermore, linkage analyses of this family exclude a large part of 17p, spanning the area deleted in other families with HNPP, as the location for the disease gene. These data strongly argue for the existence of genetic heterogeneity underlying HNPP. Results from two-point linkage analysis with markers on chromosome 1q are inconsistent with a possible involvement of the locus for HMSNIb in the present family.