Corsico et al. Monoamine oxidase is an enzyme involved in the metabolism of biogenic amines. Platelet MAO activity was normal in Type I alcoholics and in healthy controls, but was lower in Type II alcoholics, suggesting a possible biological marker for alcoholism. However, in a study by Tabakoff et al. Instead they found that monoamine oxidase activity was correlated with the time since the last drink in alcoholics, but not in controls.
Linkage studies consider the cosegregation of a particular disorder with marker genes in families.
Linkage analysis has been made easier with the use of restriction fragment length polymorphisms, or RFLPs. RFLPs are different sized fragments of DNA created by polymorphisms in the recognition sites of restriction endonucleases. However, neither of these two linkages has been confirmed. While linkage refers to cosegregation of disease and a marker allele within families, association refers to population differences. Association studies are less complicated than other forms of genetic analysis because DNA only needs to be obtained from affected individuals, and not from a large number of family members.