A suite of
behaviors characterized by radical mood swings, from euphoria to
depression. Two major, distinct
modes are recognized:
bipolar affective disorder (BPAD,
aka manic depressive illness), and unipolar
affective disorder (depression without mania). Onset in the first
case is usually the second decade, and in the third decade for the latter. Affected individuals with a
family history apparently respond better to lithium than do sporadic
cases. MZ:DZ twin concordance rates of 57%:14% (see twins and concordant trait), and studies of adoptees correlated with biological
parents, suggest some contribution of
genetic factors, but with incomplete
penetrance. MAFD is an
ambiguous multifactorial disorder. Families with affected individuals tend to show co-morbidity with schizoaffective
disorder, alcoholism, and/or
anorexia nervosa. The possibility of
genetic anticipation as an additional
mechanism has been proposed. Early
linkage studies reporting
genes on
chromosomes 11 and X (MADF2) have been retracted; other current
factors map to 18p.I.