Most individuals with Canavan disease have the neonatal/infantile form. Although such infants appear normal early in life, by age three to five months, hypotonia, head lag, macrocephaly, and developmental delays become apparent. With age, children with neonatal/infantile-onset Canavan disease often become irritable and experience sleep disturbance, seizures, and feeding difficulties. Swallowing deteriorates, and some children require nasogastric feeding or permanent feeding gastrostomies. Joint stiffness increases, so that these children resemble individuals with cerebral palsy. Children with mild/juvenile Canavan disease may have normal or mildly delayed speech or motor development early in life without regression. In spite of developmental delay most of these children can be educated in typical classroom settings and may benefit from speech therapy or tutoring as needed. Most children with mild forms of Canavan disease have normal head size, although macrocephaly, retinitis pigmentosa, and seizures have been reported in a few individuals.

The spectrum of FARS2 deficiency ranges from the infantile-onset phenotype, characterized by epileptic encephalopathy with lactic acidosis and poor prognosis (70% of affected individuals), to the later-onset phenotype, characterized by spastic paraplegia, less severe neurologic manifestations, and longer survival (30% of affected individuals). To date FARS2 deficiency has been reported in 37 individuals from 25 families. Infantile-onset phenotype. Seizures are difficult to control and may progress quickly at an early age to intractable seizures with frequent status epilepticus; some children have hypsarrhythmia on EEG. All have developmental delay; most are nonverbal and unable to walk. Feeding difficulties are common. More than half of affected children die in early childhood. Later-onset phenotype. All affected individuals have spastic paraplegia manifested by weakness, spasticity, and exaggerated reflexes of the lower extremities associated with walking difficulties; some have developmental delay/intellectual disability; some have brief seizures that resolve over time.

Severe congenital liver disease (SCOLIV) is an autosomal recessive disorder characterized by the onset of progressive hepatic dysfunction usually in the first years of life. Affected individuals show feeding difficulties with failure to thrive and features such as jaundice, hepatomegaly, and abdominal distension. Laboratory workup is consistent with hepatic insufficiency and may also show coagulation defects, anemia, or metabolic disturbances. Cirrhosis and hypernodularity are commonly observed on liver biopsy. Many patients die of liver failure in early childhood (Moreno Traspas et al., 2022).