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Pontocerebellar hypoplasia type 2
Pontocerebellar hypoplasia type 2 (PCH2) is the most common subtype of pontocerebellar hypoplasia (see this term) characterized by neonatal onset and a lack of voluntary motor development and later progressive microencephaly, generalized clonus, development of chorea and spasticity. The majority of patients will not reach puberty.
PCH2 is reported in at least 81 families to date
After an uneventful pregnancy and birth without dysmorphic features, affected neonates present usually, but not always, with dysphagia due to bucco-pharyngeal incoordination, respiratory and feeding difficulties and generalized clonus. Extrapyramidal dyskinesia with mixed spasticity such as chorea, athetosis and dystonia develop later. From infancy onward, affected children develop progressive microencephaly, central visual impairment, seizures and a severe impairment of cognitive and motor development, marked by an impaired statural motor development with failing head control, lack of voluntary hand control and the absence of speech and communication. PCH2 is often fatal in early childhood.
PCH2 is generally caused by homozygous mutations in the TSEN54 gene, most frequently a founder mutation, prevalent in families of European extraction: p.A307S/A307S or and missense mutations. Rarely mutations in the TSEN2, TSEN34 , SEPSECS (Sep (O-phosphoserine) tRNA) genes are reported.
Diagnosis is made is based on a combination of neuroradiologic and clinical findings : MRI demonstrates variable neocortical atrophy, progressive in time, flattening of the caudate nuclear heads, and pontocerebellar hypoplasia with a typical dragonfly-like cerebellar pattern on coronal sections caused by the flat hemispheres heavily reduced in size together with a comparatively spared vermis.
In case of risk for recurrence of PCH2, secure prenatal diagnosis will require by amniocentesis or chorionic villus sampling and cytogenetic analysis.
PCH2 is inherited in an autosomal recessive manner. Genetic counseling is recommended in case of family history and requires parental screening for heterozygous TSEN mutations.
Prognosis is variable; the majority of patients will not reach puberty.