A rare mitochondrial disorder due to a defect in mitochondrial protein synthesis characterized by severe intrauterine growth retardation, neonatal limb edema and redundant skin on the neck (hydrops), developmental brain defects (corpus callosum agenesis, ventriculomegaly), brachydactyly, dysmorphic facial features with low set ears, severe intractable neonatal lactic acidosis with lethargy, hypotonia, absent spontaneous movements and fatal outcome. Markedly decreased activity of complex I, II + III and IV in muscle and liver have been determined.

Shashi-Pena syndrome is characterized by distinctive facial features accompanied by variable further clinical findings. Facial features may include glabellar nevus simplex, widely spaced and prominent/proptotic eyes with epicanthal folds and ptosis, arched eyebrows, broad nasal tip, and low-set/posteriorly rotated ears. Dental anomalies may include early eruption and loss of teeth as well as small and fragile teeth. Most affected individuals have infantile hypotonia that frequently resolves over time. Macrosomia and macrocephaly are also common. Affected individuals can have variable developmental delay / intellectual disability, ranging from low-average intellectual abilities to severe intellectual disability. They often demonstrate difficulties with attention and aggressive behavior. Affected individuals may have feeding difficulties that require supportive nasogastric or gastrostomy tube feeding, skin findings (capillary malformations, deep palmar creases, hypertrichosis), skeletal anomalies (scoliosis/kyphosis, hypermobility, frequent fractures), congenital heart defects, seizures, hypoglycemia (most typically in infancy, may be due to hyperinsulinism), vision abnormalities (strabismus, amblyopia), conductive hearing loss, sleep apnea, temperature dysregulation, and global volume loss on brain MRI.

Ritscher-Schinzel syndrome-4 (RTSC4) is characterized by a constellation of congenital anomalies, including dysmorphic craniofacial features and structural brain anomalies, such as Dandy-Walker malformation (220200), hindbrain malformations, or agenesis of the corpus callosum, associated with global developmental delay and impaired intellectual development. Congenital cardiac defects have been reported in 1 family (summary by Ritscher et al., 1987 and Jeanne et al., 2021). For a discussion of genetic heterogeneity of Ritscher-Schinzel syndrome, see RTSC1 (220210).

Chilton-Okur-Chung neurodevelopmental syndrome (CHOCNS) is characterized mainly by global developmental delay with variably impaired intellectual development and occasional speech delay. Most patients have behavioral abnormalities, including autism spectrum disorder, ADHD, and aggression. About half of patients have dysmorphic facial features, and about half have nonspecific brain abnormalities, including thin corpus callosum. Rare involvement of other organ systems may be present. At least 1 child with normal development at age 2.5 years has been reported (Chilton et al., 2020).