Pontocerebellar hypoplasia type 9 (PCH9) is an autosomal recessive neurodevelopmental and neurodegenerative disorder characterized by severely delayed psychomotor development, progressive microcephaly, spasticity, seizures, and brain abnormalities, including brain atrophy, thin corpus callosum, and delayed myelination (summary by Akizu et al., 2013). For a general phenotypic description and a discussion of genetic heterogeneity of PCH, see PCH1 (607596).

Lissencephaly-8 (LIS8) is an autosomal recessive neurologic disorder characterized by delayed psychomotor development, intellectual disability with poor or absent speech, early-onset refractory seizures, and hypotonia. Brain imaging shows variable features, including cortical gyral abnormalities and hypoplasia of the corpus callosum, brainstem, and cerebellum (Jerber et al., 2016). For a general description and a discussion of genetic heterogeneity lissencephaly, see LIS1 (607432).

Autosomal recessive primary microcephaly-17 (MCPH17) is a severe neurologic disorder characterized by very small head circumference that is apparent at birth and worsens over time (up to -12 SD). Affected individuals have delayed psychomotor development, intellectual disability, spasticity, axial hypotonia, and dysmorphic features. Brain imaging shows a simplified gyral pattern; more severe cases have lissencephaly with hypoplasia of the brainstem and cerebellum (summary by Harding et al., 2016). For a phenotypic description and a discussion of genetic heterogeneity of primary microcephaly, see MCPH1 (251200).

Complex cortical dysplasia with other brain malformations-9 is a severe autosomal recessive disorder characterized by profoundly impaired motor and cognitive development apparent from early infancy. Affected individuals develop intractable seizures and are unable to speak or ambulate. Brain imaging shows pachygyria as well as hypogenesis of the corpus callosum and other variable brain abnormalities. The phenotype results from impaired cortical neuronal migration (summary by Schaffer et al., 2018). For a discussion of genetic heterogeneity of CDCBM, see CDCBM1 (614039).

Autosomal recessive spinocerebellar ataxia-20 is a neurodevelopmental disorder characterized by severely delayed psychomotor development with poor or absent speech, wide-based or absent gait, coarse facies, and cerebellar atrophy (summary by Thomas et al., 2014).

Complex cortical dysplasia with other brain malformations-10 (CDCBM10) is an autosomal recessive neurodevelopmental disorder characterized by severely impaired global development associated with abnormalities on brain imaging, including lissencephaly, cortical dysplasia, subcortical heterotopia, and paucity of white matter. The disorder results from defective neuronal migration during brain development. Affected individuals often develop seizures, are unable to walk, and do not acquire language (summary by Lee et al., 2019). For a discussion of genetic heterogeneity of CDCBM, see CDCBM1 (614039).

Permanent neonatal diabetes mellitus-3 (PNDM3) is characterized by the onset of mild to severe hyperglycemia within the first months of life, and requires lifelong therapy (summary by Babenko et al., 2006). Some patients also have neurologic features, including developmental delay and epilepsy (Proks et al., 2006; Babenko et al., 2006). The triad of developmental delay, epilepsy, and neonatal diabetes is known as DEND. For a discussion of genetic heterogeneity of permanent neonatal diabetes mellitus, see PNDM1 (606176).

Pontocerebellar hypoplasia type 14 (PCH14) is a severe autosomal recessive neurodevelopmental disorder characterized by congenital onset of progressive microcephaly and poor or absent psychomotor development with severely impaired intellectual development apparent from birth. Other features may include hypotonia, spastic quadriplegia, and early-onset seizures. Brain imaging shows pontocerebellar hypoplasia, agenesis or partial agenesis of the corpus callosum, and sometimes a simplified gyral pattern. Early death may occur (summary by et al., 2021). For a phenotypic description and a discussion of genetic heterogeneity of PCH, see PCH1A (607596).

Pontocerebellar hypoplasia type 15 (PCH15) is a severe autosomal recessive neurodevelopmental disorder characterized by congenital onset of progressive microcephaly and poor or absent psychomotor development with severely impaired intellectual development apparent from birth. Other features may include spastic quadriplegia, early-onset seizures, and chronic anemia and thrombocytopenia. Brain imaging shows pontocerebellar hypoplasia and partial agenesis of the corpus callosum (summary by et al., 2021). For a phenotypic description and a discussion of genetic heterogeneity of PCH, see PCH1A (607596).

Zaki syndrome (ZKS) is characterized by developmental delay, progressive microcephaly, and short stature, as well as dysmorphic features including sparse scalp hair, cupped ears, wide nose and mouth, short philtrum, and high-arched palate. Other variable features have been observed, including ocular, skeletal, cardiac, and renal anomalies (Chai et al., 2021).