Familial occurrence of a small, supernumerary metacentric chromosome in phenotypically normal women.

Atypical, additional, metacentric chromosomes, approximating in size to that of G group chromosomes, have been reported in patients with undifferentiated types ofmental retardation and congenital malformation (Fr0land, Holst, and Terslev, 1963; Gustavson, Atkins, and Patricks, 1964; Taft, Dodge, and Atkins, 1965; Tamburro and Johnson, 1966; Ferrante et al., 1968; Ishmael and Laurence, 1968; Mukherjee et al., 1968), with Down's syndrome (Dekaban, 1965; Townes, 1968), with psychosis (Anders et al., 1968), and with oligospermia (Smith et al., 1965). The presence of additional 'minute' metacentrics has been noted in cases recorded by Hulten et al. (1966), by Fischer and Haslund (1968), and by Ginsberg, Dignan, and Soukup (1968). Occasionally, an extra metacentric has also been found in normal, healthy individuals (Smith et al., 1965; Townes, 1968). The derivation and possible significance of these supernumerary fragments is obscure, and substantial phenotypic variation has been associated with their presence in the human karyotype. This report presents data on a family in which each of three phenotypically normal women has an additional small metacentric chromosome, and provides evidence as to the possible identity of the extra fragment.