Familial X-linked mental retardation with a marker X chromosome and its relationship to macro-orchidism.

It has been suggested that the form of X-linked mental retardation with macro-orchidism and the form associated with a marker X chromosome (fragile site at Xq27 or 28) are the same entity. Although our data support this hypothesis, one family from the literature does not. Data are presented suggesting that actual measurements are required for accurate evaluation of testicular size.