RASSF1 and Down syndrome: Finally, in other studies on papillary carcinoma of the thyroid it was shown that abnormal methylation may occur in tumour cells, and is probably responsible for loss or for decreased expression of several genes including TSH receptor (TSHR) (Xing et al, 2003a) the Pendred syndrome gene SLC26A4 (Xing et al, 2003b), the Ras association domain family 1A gene (RASSF1A) (Schagdarsurengin et al, 2002), the metallothionein heavy metal binding protein gene (MT1G) (Huang et al, 2003) and the high-affinity cellular retinoic binding protein (CRABP1) (Huang et al, 2003).