Point mutations of the connexin32 (GJB1) gene in X-linked dominant Charcot — Marie — Tooth neuropathy

Abstract

Ten families with X-linked dominant CMT neuropathy (CMTX1) were screened for point mutations of the connexin32 (Cx32, GJB1) gene. Two families showed missense mutations, respectively an A-->G transition at amino acid 102 (glutamate to glycine) and a C-->T transition at amino acid 142 (arginine to tryptophan). Three families showed nonsense mutations, respectively a C-->T transition at amino acid 22 (arginine to stop) a G-->T transversion at amino acid 186 (glutamate to stop), and a T-->A transversion at amino acid 217 (cysteine to stop). Five CMTX1 neuropathy families showed no evidence of point mutations of the connexin32 coding sequence. These findings suggest that the CMTX1 neuropathy genotype is heterogeneous or the result of promoter mutations, 3'-untranslated region mutations or exon/intron splice site mutations. Four of the reported mutations created or destroyed restriction enzyme sites: a HaeIII restriction enzyme site was destroyed by the mutation at amino acid position 22, a HpaII site was eliminated at amino acid position 142, a Bfal restriction site was created by the mutation at amino acid 186 and a Ddel restriction site was created by the mutation at amino acid 217. These changes allowed us to test family members for the mutations and observe the segregation of the disease with the mutations.

Phenotypes of X-linked Charcot-Marie-Tooth disease and altered trafficking of mutant Connexin 32 (GJB1)

“…A correlation between Cx32 mutations and disease severity in CMTX has been suggested, but is still controversial in some aspects (Fairweather et al 1994;Ionasescu 1995;Ionasescu et al 1994Ionasescu et al , 1996Fischbeck et al 1996;Bone et al 1995Bone et al , 1997Janssen et al 1997;Birouk et al 1998;Sander et al 1998;Nelis et al 1999;Hahn et al 1999, Nicholson et al 1999. A dominant negative effect, loss of function effect, and interaction among different connexins have been proposed to explain the molecular mechanism of the genotype/ phenotype correlation in CMTX (Omori et al 1996;Deschênes et al 1997;Oh et al 1997;Ressot et al 1998;Sahenk and Chen 1998;Hahn et al 1999;Nicholson et al 1999;Fischbeck et al 1999).…”

“…Cx32 is a gap junction protein found mainly in the paranodal regions and the Schmidt-Lanterman incisures of peripheral nerve myelin; six connexin molecules assemble to form one connexon and act as gap junction channels providing direct intercellular communications (Bergoffen et al 1993;Scherer et al 1995). Since 1993, more than 200 different mutations, affecting every portion of the gene (Bergoffen et al 1993, Fairweather et al 1994Ionasescu 1995;Ionasescu et al 1994Ionasescu et al , 1996Bone et al 1995Bone et al , 1997Fischbeck et al 1996;Janssen et al 1997;Birouk et al 1998;Sander et al 1998;Nelis et al 1999;Hahn et al 1999), have been identified. However, only several mutations have been investigated in terms of their ability to form functional gap junctions and in terms of their relations with other connexins (Bruzzone et al 1994;Omori et al 1996;Deschênes et al 1997;Oh et al 1997;Ressot et al 1998;Sahenk and Chen 1998;Nicholson and Corbett 1999;Fischbeck et al 1999).…”

Connexin32 gene mutations in X-linked dominant Charcot-Marie-Tooth disease (CMTX1)

“…Following the demonstration that mutations in connexin32 segregate with CMTX1 (Bergoffen et al 1993), other mutations have been described (Bergoffen et al 1993;Bone et al 1995a;Bruzzone et al 1994;Cherryson et al 1994;Fairweather et al 1994;Ionasescu et al 1994Ionasescu et al , 1995Orth et al 1994;Ressot et al 1996;Tan et al 1994Tan et al , 1996. These mutations reveal which parts of the connexin32 molecule are important for properly functioning gap junctions.…”

“…The mutations are summarized in Table 1. Three mutations at nucleotides 126, 249, and 477 have previously been described in presumably unrelated families (Bergoffen et al 1993;Fairweather et al 1994;Ionasescu et al 1994;Bone et al 1995a;Ressot et al 1996).…”

“…In the X-linked dominant form (McKusick no. 302800) located at Xq13.1 (Gal et al 1985;PericakVance et al 1995), mutations have been reported in the connexin32 gene (Bergoffen et al 1993;Bone et al 1995a;Cherryson et al 1994;Fairweather et al 1994;Ionasescu et al 1994Ionasescu et al , 1995Orth et al 1994;Ressot et al 1996;Tan and Ainsworth 1994;Tan et al 1996) The connexins comprise a family of structural proteins important for the formation of gap junctions. Hexameric assemblies of connexins (connexons) interact with their counterpart in adjacent cells to form gap junctions.…”