Pontocerebellar hypoplasia type 5

Pontocerebellar hypoplasia type 5 (PCH5) is an extremely rare and severe neurodegenerative disorder characterized by pronounced underdevelopment (hypoplasia) of the pons and cerebellum — structures in the brainstem and hindbrain critical for motor coordination, balance, and many autonomic functions. PCH5 is distinguished from other forms of pontocerebellar hypoplasia by its prenatal onset with fetal seizures, and it presents at birth with severe encephalopathy, profound intellectual disability, and seizures that are often intractable. Affected infants typically exhibit microcephaly, spasticity, and minimal voluntary movement. The condition has been associated with mutations in the TSEN54 gene, which encodes a subunit of the tRNA splicing endonuclease complex, linking it molecularly to several other PCH subtypes. Clinically, PCH5 affects the central nervous system profoundly. Neuroimaging reveals severe cerebellar and pontine hypoplasia, with a characteristic "dragonfly" or "butterfly" appearance of the cerebellum on MRI due to preferential involvement of the cerebellar hemispheres relative to the vermis. Affected neonates may present with respiratory difficulties, feeding problems, and opisthotonus. Fetal seizures, which may be detected prenatally, are a hallmark feature that helps distinguish PCH5 from other PCH subtypes. The prognosis is extremely poor, with most affected individuals dying in the neonatal period or early infancy. There is currently no curative treatment for PCH5. Management is entirely supportive and palliative, focusing on seizure control with anticonvulsant medications, nutritional support (often via nasogastric or gastrostomy tube feeding), respiratory support, and physical therapy. Genetic counseling is recommended for affected families. Research into the molecular mechanisms underlying tRNA splicing endonuclease complex dysfunction continues, but no disease-modifying therapies are available at this time.

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