[The human genome--chromosome 20].

There is an increasing interest on one of the smallest human chromosomes as it is shown by the First International Symposium on the Human Chromosome 20 and by the genetic map prepared by EUROGEN. The conserved part of the long arm of human chromosome 20 is synthenic with the distal part of the mouse chromosome 2 allowing for some analogies between them. Human chromosome 20 contains several important genes for the human pathology. Mutations of one of them, the vasopressin-neurophysin II gene, are responsible for hereditary neurohypophyseal diabetes insipidus. Severe combined immunodeficiency due to adenosin deaminase deficiency is the first human disorder successfully treated by somatic gene therapy. Spongiform encephalopathies are related to mutation and/or polymorphisms of the PRNP amyloid gene. One form of benign familiar neonatal convulsions is mapped to a specific locus on chromosome 20. In some families, maturity onset diabetes of the young (MODY) is caused by alterations of a hypothetical gene closely linked to the ADA locus. Allegile syndrome is often associated with deletions and microdeletions of the short arm of the chromosome. Finally, deletions of the long arm of the chromosome is a frequent finding in several hematologic malignities, specifically in myeloproliferative disorders and myelodysplastic syndromes.