Genetic variation analysis of MLP, TFAP2A, and CSK in patients with neural tube defects.

Neural tube defects (NTDs) are congenital malformations which arise from incomplete closure of the neural tube during early embryogenesis. The most common types found in humans are spina bifida and anencephaly. These can occur together in a single family and in some cases even in one person. About 70–80% of all human NTDs show complex or multifactorial inheritance patterns, indicating that both genetic and environmental factors play a part in the aetiology of this malformation. Folic acid supplementation reduces the incidence of human and mouse NTDs. Furthermore, supplementation of myo-inositol reduces the incidence of NTDs substantially in the NTD mouse model, curly tail. In curly tail embryos, supplementary myo-inositol increases the flux through the inositol/lipid cycle, stimulating protein kinase C (Pkc) activity. Protein kinase C phosphorylates and thus activates several proteins that are directly involved in the formation of the neural tube, such as Ap2-α and Mlp (fig 1). 10 Ap2-α null as well as heterozygous and chimeric knockout mice have exencephaly. Mlp knockout mice have exencephaly and spina bifida. 15 Apart from the genes involved in inositol signalling, NTDs also occur in mice deficient for the Csk gene. This gene encodes a negative regulator of Src family tyrosine kinases and acts through phosphorylation of the Src family members at their C-terminal tyrosine residue (fig 1). Csk is involved in the organisation of the cytoskeleton. As outlined above, Ap2-α, Mlp, and Csk are associated with NTDs in mice. In humans, Stegmann et al, using a case-control study found no involvement of the human orthologue of Ap2-α, TFAP2A, in the aetiology of human NTDs. Furthermore, with transmission disequilibrium test (TDT) analysis for a small set of simplex families, no association was found between the human MLP gene and spina bifida. In this paper, with DNA material from a large panel of patients with NTDs, we present the results of an extensive mutation analysis in the genes coding for TFAP2A, MLP, and CSK.