· Hereditary diseases with a genetic basis have been treatable since the introduction of molecular genetic techniques just over two decades ago, and their study forms a fundamental part of integrated, modern medicine. Almost all human ailments have an element of genetic variability, although there are some that are caused, fundamentally, by the action of only one mutant gene (monogenic diseases) - these are the type most susceptible to an effective molecular diagnosis. At the moment some 13,000 diseases have been identified where heredity depends essentially on the action of one major or principal gene. Of them, 10,000 genes have been identified (Online Mendelian Inheritance in Man, OMIM: www.ncbi.nlm.nih.gov) of which some 3,000 have been cloned or isolated and the respective pathogenetic properties of approximately 1,000 are known. In most cases, it is therefore possible to do a molecular diagnosis of the ailments, identifying the corresponding alterations or mutations, and to produce an accurate genetic consultation for the patients and their relatives.

The genetic analysis tests are to be considered as index case studies (where the diagnosis is confirmed and a differential diagnosis and classification of the mutation are done) of subjects and their families. The latter allows for the diagnosis of carriers and for the collection of information (often indispensable) in order to make a global hereditary gene study. That is to say, usually one works with a "genealogy in progress".

Often genetic analysis tests do not specifically search out the causal mutation either because it is not known or because determining it is too costly; instead they employ an indirect method of gene linkage or "gene tracking".

Our Centre for Molecular Genetic Diagnosis of hereditary diseases is a pioneer in Spain in the study of genetic medicine and has been carrying out its activities   in medical assistance and research since 1990.