Curiously, complete absence of detectable CSB protein does not invariably cause CS: a nonsense mutation at codon 77 in CSB exon 2 causes only mild UV-sensitive syndrome (UVSS) with no syndromic or developmental components [20], whereas complete absence of CSB resulting from deletion of 5' UTR sequences including exon 1 causes classical early onset CS [22]. Here, ERCC6 is linked to Cowden syndrome 1.