Sequence variations of NKX2-5 and HAND1 genes in patients with atrial isomerism

Atrial isomerism is a congenital disorder, which is characterized by lateralization defects in normally asymmetrical developing organs like the heart. Atrial isomerism is supposed to be caused by molecular defects during early development. The NKX2-5 is a cardiac specific transcription factor, which initiates and regulates downstream transcriptional cascades of cardiogenesis. The HAND1 is another transcription factor expressed in the heart, and it is characterized by an asymmetrical pattern of expression. In this study, we aimed to test whether mutations in NKX2-5 and HAND1 genes play a role in the etiology of atrial isomerism.

This case-control study consisted of 70 patients who underwent surgical treatment for congenital heart defects including atrial isomerism, 80 healthy subjects (HAND1 gene) and 40 healthy subjects (NKX2-5 gene). All exons and exon-intron boundaries of NKX2-5 and HAND1 genes were analyzed by SSCP, and suspected samples were sequenced for mutation analysis. Digestion with appropriate restriction enzymes was performed for analysis of known mutations and polymorphisms. The frequencies of the alleles and the genotypes were compared among patient and control groups using the Chi-square and the Fisher tests when appropriate.

In intronic region of HAND1 gene, we identified a C>G substitution both in patients and controls. Frequency of mutant allele (11, 42%) was found higher (p=0.046) in patient group than that of the control group (2.5%). Association between atrial isomerism and genotypes with mutant allele was found borderline significant (p=0.054). In NKX2-5 gene, we identified heterozygous Q170X (Gln170ter) mutation in one patient. We did not found any correlation between defined sequence variations and clinical properties of the patients.

Our results suggest that mutations or sequence variations in HAND1 or NKX2-5 genes may play role in etiology or pathogenesis of atrial isomerism.