Biased Paternal Transmission of TRH Variant to Female down Syndrome Probands: Possible Correlation with Low Breast Cancer Frequency

Abstract

Thyroid malfunction is more common in individuals with Down syndrome (DS) than in the general population. It has been hypothesized that thyroid may influence cancer risk. Individuals with DS are at greater risk of developing leukemia than the general population, while solid tumors especially breast cancer (BC) are rare. BC patients have higher levels of circulating thyroid-stimulating hormone (TSH) and prolactin (PRL), both regulated by the thyrotropin-releasing hormone (TRH), a hypothalamic tripeptide. This study was aimed at investigating the status of TRH functional polymorphisms in subjects with DS and BC. Unrelated families with DS probands (n=180), individuals with BC (n=99) and ethnically matched controls (n=216) were recruited. Genomic DNA isolated from peripheral blood was subjected to PCR amplification followed by DNA sequence analysis. Data obtained were analyzed by population- and family-based statistical analysis. Among 30 studied sites, only 2 (rs7645772 and rs13097335) were polymorphic. Case-control analysis showed a lack of any significant association with DS, while the rs13097335 GG and GT genotype frequency was significantly different in the BC samples. A paternal-biased transmission of the G allele was observed in female DS probands. It may be concluded that rs13097335 may have a protective role toward the development of BC.