Van Gemund et al. (1969) described 2 boys, offspring of first-cousin parents, who were 'small for dates' at birth and showed marked dwarfism, severe mental retardation, and congenital deafness. One relative was congenitally deaf with normal stature and ... Van Gemund et al. (1969) described 2 boys, offspring of first-cousin parents, who were 'small for dates' at birth and showed marked dwarfism, severe mental retardation, and congenital deafness. One relative was congenitally deaf with normal stature and intellect. A maternal uncle showed marked dwarfism and severe mental retardation, but was not deaf. Insulin-induced hypoglycemia evoked excessively high levels of immunoreactive hGH. They did not show increased sensitivity to fatty acid levels. Orally administered glucose suppressed hGH and evoked insulin secretion. Exogenous hGH did not decrease urinary nitrogen excretion or increase urinary hydroxyproline excretion. Growth-promoting effects of exogenous testosterone were intact. Unresponsiveness to somatotropic effects of hGH was postulated. The consanguinity suggests autosomal recessive inheritance. Since a maternal uncle had dwarfism and mental retardation, X-linked recessive inheritance is a possibility.