Any autosomal dominant non-syndromic intellectual disability in which the cause of the disease is a mutation in the CACNG2 gene.

The Cincinnati type of acrofacial dysostosis is a ribosomopathy characterized by a spectrum of mandibulofacial dysostosis phenotypes, with or without extrafacial skeletal defects (Weaver et al., 2015). In addition, a significant number of neurologic abnormalities have been reported, ranging from mild delays to refractory epilepsy, as well as an increased incidence of congenital heart defects, primarily septal in nature (Smallwood et al., 2023).

You-Hoover-Fong syndrome (YHFS) is an autosomal recessive disorder with clinical features of global developmental delay, impaired intellectual development, dysmorphic facial features, microcephaly, abnormal movements, and abnormal auditory and visual function (You et al., 2016).

Neurodevelopmental disorder with seizures and speech and walking impairment (NEDSSWI) is an autosomal recessive disorder with onset in infancy. Patients show global developmental delay, particularly of speech acquisition, as well as walking difficulties due to hypotonia, hypertonia, spasticity, or poor coordination. Other features include seizures, mild dysmorphic features, and variable short stature. The pregnancies tend to be complicated by hyper- or hypotension (summary by Ganapathi et al., 2019).

ATN1-related neurodevelopmental disorder (ATN1-NDD) is characterized by developmental delay / intellectual disability. Other neurologic findings can include infantile hypotonia, brain malformations, epilepsy, cortical visual impairment, and hearing loss. Feeding difficulties, present in some individuals, may require gastrostomy support when severe; similarly, respiratory issues, present in some, may require respiratory support after the neonatal period. Distinctive facial features and hand and foot differences are common. Other variable findings can include cardiac malformations and congenital anomalies of the kidney and urinary tract (CAKUT). To date, 18 individuals with ATN1-NDD have been identified.

Autosomal recessive limb-girdle muscular dystrophy-28 (LGMDR28) is characterized by progressive muscle weakness affecting the proximal and axial muscles of the upper and lower limbs. The age at onset is highly variable, usually in the first decade, although onset in the fourth decade has also been reported. The disorder can be rapidly progressive or show a slower course. Most patients have limited ambulation or become wheelchair-bound within a few decades, and respiratory insufficiency commonly occurs. Laboratory studies show increased serum creatine kinase and elevated fasting blood glucose levels, although cholesterol is normal. EMG shows a myopathic pattern; muscle biopsy is generally unremarkable, but can show nonspecific myopathic or dystrophic features (Yogev et al., 2023; Morales-Rosado et al., 2023). For a discussion of genetic heterogeneity of autosomal recessive limb-girdle muscular dystrophy, see LGMDR1 (253600).