A screen for mutations in human homologues of mice exencephaly genes Tfap2alpha and Msx2 in patients with neural tube defects

Background: Very little is known about the identity of genetic factors invo lved in the complex etiology of nonsyndromic neural tube defects (NTD). Pot ential susceptibility genes have emerged from the vast number of mutant mou se strains displaying NTD. Reasonable candidates are the human homologues o f mice exencephaly genes Tfap2 alpha and Msx2, which are expressed in the d eveloping neural tube. Methods: A single-strand conformation analysis (SSCA) mutation screen of th e coding sequences of TFAP2 alpha and MSX2 was performed for 204 nonsyndrom ic NTD patients including cases of anencephaly (n = 10), encephalocele (n = 8), and spina bifida aperta, SEA (n = 183). A selected number of SEA patie nts was additionally tested for specific mutations in MTHFD, FR alpha, and PAX1 already shown to be related to NTD. Results: Two TFAP2 alpha point mutations in individual SEA patients were si lent on the amino acid level (C308C, T396T). On nucleic acid level, these m utations change evolutionary conserved codons and thus may influence mRNA p rocessing and translation efficiency. One SEA patient displayed an exonic 9 -bp deletion in MSX2 leading to a shortened and possibly less functional pr otein. None of these mutations was found in 222 controls. Seven polymorphis ms detected in TFAP2 alpha and MSX2 were equally distributed in patients an d controls. Patients with combined heterozygosity of an exonic MSX2 and an intronic TFAP2 alpha polymorphism were at a slightly increased risk of NTD (OR 1.71; 95% CI 0.57-5.39). Conclusions: Although several new genetic variants were found in TFAP2 and MSX2, no statistically significant association was found between NTD cases and the new alleles or their combinations. Further studies are necessary to finally decide if these gene variants may have acted as susceptibility fac tors in our individual cases. Teratology 63:167-175, 2001. (C) 2001 Wiley-L iss, Inc.