Classification of Pontocerebellar Hypoplasia: Where does it End?

Pontocerebellar hypoplasia (PCH) represents a heterogeneous group of congenital neurodegenerative diseases. Patients are afflicted by severe motor and mental impairments and most patients die at a young age. The hallmark of PCH is hypoplasia of the cerebellum and the pons, often in combination with supratentorial involvement. PCH is caused by autosomal recessive mutations in genes, most of which play a role in RNA metabolism. Twelve types (PCH1-12) are described, mainly based on clinical features. Identification of the responsible genes showed that the clinical classification did not match with the genetic classification leading to definition of subtypes. The authors expect that the increasing use of next-generation sequencing will lead to the identification of even more new PCH genes, widening the genetic and phenotypical spectrum. This will expand the classification and make it more complex. Therefore, the authors suggest that a new adjusted classification should be formulated to save the functionality of the PCH group.