Lack of evidence for connexin 43 gene mutations in human autosomal recessive lateralization defects

Heterotaxy is the failure of the developing embryo to establish normal left-right asymmetry, which is often associated with multiple malformations. Previous studies have identified different mutations in the cytoplasmic tail of the connexin 43 (cx 43) gene in six patients from a series of six sporadic cases with defects of laterality and severe heart malformations. These cases showed that of the genes involved in lateralization defects with autosomal recessive transmission, cx 43 was the most important. This result was challenged by two different teams, which, on sequencing only the carboxyl terminal end of the cx 43 gene in 30 patients, found no mutations. To assess the responsibility of the cx 43 gene in human autosomal recessive lateralization defects, we tested its involvement in a selected group of 25 patients (19 familial cases) with a wide variety of lateralization defects and cardiovascular malformations. The whole coding sequence and direct flanking sequences were screened for mutations, both by single strand conformation analysis and direct fluorescent sequencing. We could only detect a single base pair insertion in the 3' untranslated region of one patient. To test the possibility of mutations in other parts of the cx 43 gene, the gene was located onto the physical map of chromosome 6, and flanking polymorphic markers were genotyped. Haplotype analysis excluded the cx 43 gene locus in nearly all of the familial cases of lateralization defects. Thus, our results do not support the suggestion that this gene is implicated in human autosomal recessive lateralization defects.