Pituitary dwarfism is a genetically heterogeneous group of disorders associated with a variety of pathogenetic mechanisms which may involve any level of the hypothalamic-pituitary-
somatomedin-peripheral tissue axis. Developmental defects of the pituitary, such as congenital absence of the pituitary, and developmental defects of the hypothalamus, such as
anencephaly and
holoprosencephaly, have been described. Degeneration of the hypothalamus and pituitary, as in
histiocytosis X, may also result in
pituitary dwarfism. In "idiopathic" forms of
pituitary dwarfism, defects limited to either the hypothalamus or pituitary have been suggested by releasing
hormone stimulation studies and it is quite likely that specific defects of the hypothalamus, and pituitary, as well as defects in releasing hormonal synthesis and secretion and
growth hormone synthesis and secretion all exist. In
Laron dwarfism the basic defect appears to lie in the ability to generate
somatomedin, in the Pygmy the defect appears to involve peripheral unresponsiveness to
somatomedin. Further pathologic studies of the hypothalamus and pituitary in
pituitary dwarfism; analysis of
growth hormone and
somatomedin cellular receptors; and elucidation of the structure of
growth hormone releasing factor and techniques for its synthesis and assay should allow for the delineation of the specific pathogenetic mechanism in each of these syndromes.