The 5HTTLPR is perhaps one of the best studied human polymorphisms. The polymorphism consists of two common alleles in European populations, a short (s) variant with 12 copies of a 22 bp repeat element and a long (l) variant, which has 14 copies of the repeat element. The properties of the s allele have been extensively examined and it has been associated with decreased mRNA transcription [Heils et al., 1996; Lesch et al., 1996; Bradley et al., 2005], decreased protein production [Stoltenberg et al., 2002] and increased vulnerability to alcohol dependence (AD) and MD as demonstrated by meta-analyses [Lotrich and Pollock, 2004; Feinn et al., 2005].
