Molecular biology. (techniques to identify genes involved in alcoholism)(The Genetics of Alcoholism)

Recent advances in molecular biology techniques permit scientists to identify genetic contributions to alcoholism. Two main types of technology are commonly used to identify genes that cause or predispose a person to a disease: positional cloning techniques and candidate gene techniques. Positional cloning techniques allow disease genes to be identified based solely on their location within the genome without prior knowledge of the gene's function. Techniques for confirming the role of candidate genes rely on sufficient prior understanding of the disease process to implicate possible disease-related genes. Scientists use cloning techniques or the application of certain enzymes to reproduce a candidate gene in sufficient quantity for study. As the human genome project progresses and the gene map becomes increasingly complete, more and more disease genes will be identified through a combination of positional cloning and the candidate gene approach. Key Words: AOD dependence; gene; research; laboratory method; molecular genetics; genome; genetic mapping; genetic linkage; environmental factors; etiology

Alcoholism is a complex disease caused by a matrix of biological, psychological, and social factors. Although family, twin, and adoption studies have established a genetic contribution to alcoholism, the nature of this contribution is unknown. Researchers are using molecular biology techniques to identify and elucidate the mode of action of genes that predispose people to alcoholism.

Genes and Disease

The genetic "blueprint" that determines the structure and composition of any living organism resides within the DNA molecule. DNA forms the backbone of each of the 23 pairs of chromosomes in the nucleus of every cell in the human body. A DNA molecule comprises long chains of chemical subunits called nucleotides.

Genes are specific sequences of nucleotides that provide the code for particular genetic traits. Each gene directs the synthesis of a different protein from chemical subunits called amino acids. The sequence of nucleotides in a gene determines the order of different amino acids in the finished protein and, hence, the nature of the protein.(1)

Some proteins form structural components of cells and tissues. Other proteins (e.g., enzymes) perform vital functions. A normal range of genetic variability contributes to diversity among the human population (e.g., racial characteristics and variation in eye color). Variation at a key site within a gene, however, may render the gene defective. Defective genes produce defective proteins; the resulting structural or functional abnormality forms the basis of genetic disease.

Chromosomes are inherited in pairs, one set of 23 from each parent. Consequently, each cell contains two copies of each gene. Diseases caused by a defect in a single gene are described as Mendelian, after the Austrian monk Gregor Mendel, who formulated many of the principles of inheritance in the …