Dr Quintana-Murci's data were drawn from a project called HapMap, which catalogues what are known as single-nucleotide polymorphisms, or SNPs.

They analyzed more than 1, 400 single nucleotide polymorphisms, or SNPs for short, to see if any particular SNPs were more frequently carried by schizophrenia patients than unaffected people.

Two single nucleotide polymorphisms (SNPs), both located onthe chromosomal region 2p35, had the highest degree of associationwith alcohol dependence in a relatively homogenous patient population.