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inherited abnormalityany genetically determined malfunction. These fall into two main types:
- those controlled by single genes where, for example, a biochemical process is disrupted by faulty enzymes coded by abnormal alleles such as those causing ALBINISM (See also INBORN ERRORS OF METABOLISM). In other cases, such as SICKLE-CELL ANAEMIA, a molecule is produced that does not function in the normal way.
- those produced by chromosomal changes (see CHROMOSOMAL MUTATION). Here, loss or addition of parts or of whole chromosomes can have serious effects. Changes to autosomal chromosomes (see DOWN'S SYNDROME) often produce more severe effects than to sex chromosomes (see KLINEFELTER'S SYNDROME).