A rare disorder characterized by the partial separation of the cerebral hemispheres. It is associated with mutations in the SIX3 gene.

Holoprosencephaly-9 refers to a disorder characterized by a wide phenotypic spectrum of brain developmental defects, with or without overt forebrain cleavage abnormalities. It usually includes midline craniofacial anomalies involving the first branchial arch and/or orbits, pituitary hypoplasia with panhypopituitarism, and postaxial polydactyly. The disorder shows incomplete penetrance and variable expressivity (summary by Roessler et al., 2003 and Bertolacini et al., 2012). For general phenotypic information and a discussion of genetic heterogeneity of holoprosencephaly, see HPE1 (236100).

Combined pituitary hormone deficiency-8 (CPHD8) is an autosomal dominant disorder characterized by deficiency of one or more of the pituitary hormones. Affected individuals have short stature due to growth hormone (GH; 139250) deficiency with variable deficiencies of other pituitary hormones, including TSH (see 188540), ACTH, and LH/FSH (see 118850). Posterior pituitary deficiency leading to central diabetes insipidus is rare (Bashamboo et al., 2017). Many patients are diagnosed with 'pituitary stalk interruption syndrome' (PSIS), which is characterized by a thin or absent pituitary stalk, absent or ectopic posterior pituitary, and hypoplasia of the anterior pituitary demonstrated on brain imaging, although this classic triad may be incomplete. Brauner et al. (2020) noted the complex phenotypic and genetic heterogeneity of PSIS, and concluded that it is a feature of genetic disorders or syndromes rather than a specific clinical entity. For a discussion of genetic heterogeneity of combined pituitary hormone deficiency, see CPHD1 (613038).