Pontocerebellar hypoplasia (PCH) is a heterogeneous group of rare neurodegenerative disorders caused by genetic mutations and characterised by progressive atrophy of various parts of the brain such as the cerebellum or brainstem (particularly the pons). Where known, these disorders are inherited in an autosomal recessive fashion. There is no known cure for PCH.
Pontocerebellar hypoplasia is classified as follows:
|Type||OMIM||Gene||Locus||Distinctive features||Alternate names|
|PCH1A||607596||VRK1||14q32||Anterior horn cell degeneration||Spinal muscular atrophy with pontocerebellar hypoplasia (SMA-PCH)|
|PCH1B||614678||EXOSC3||9p13.2||Decreased body tone, respiratory insufficiency, muscle atrophy|
|PCH2A||277470||TSEN54||17q25.1||Dyskinetic movements, seizures (frequently)||Volendam neurodegenerative disease|
|PCH2D||613811||SEPSECS||4p15.2||Progressive cerebello-cerebral atrophy (PCCA)|
|PCH3||608027||CLAM||7q11–q21||Seizures, short stature, optic atrophy||CLAM-PCH, cerebellar atrophy with progressive microcephaly|
|PCH4||225753||TSEN54||17q25.1||Severe prenatal form of PCH2 with excess fluid in the amniotic sac, muscle contractures, brief involuntary muscle twitching, brief episodes without breathing, and early death following birth|
|PCH5||610204||unknown||unknown||Severe prenatal form, described in one family||Olivopontocerebellar hypoplasia (OPCH)|
|PCH6||611523||RARS2||6q15||Severe encephalopathy in the newborn with hypotonia, and inconstantly: intractable seizures, edema, increased lactate blood levels, mitochondrial respiratory chain defects|
|PCH7||—||unknown||unknown||Hypotonia, apneic episodes, seizures, vanishing testis|
Signs and symptoms
There are different signs and symptoms for different forms of pontocerebellar hypoplasia, at least six of which have been described by researchers. All forms involve abnormal development of the brain, leading to slow development, movement problems, and intellectual impairment.
The following values seem to be aberrant in children with CASK gene defects: lactate, pyruvate, 2-ketoglutaric acid, adipic acid, and suberic acid which seems to support the thesis that CASK affects mitochondrial function.
Pontocerebellar hypoplasia is caused by mutations in genes including VRK1 (PCH1); TSEN2, TSEN34 (PCH2); RARS2 (PCH6); and TSEN54 (PCH2 and PCH4). The genes associated with PCH3 and PCH5 have not yet been identified.
The mutated genes in PCH are autosomal recessive, which means that parents of an affected child each carry only one copy of the damaged gene. In each parent the other copy performs its proper function and they display no signs of PCH. A child inheriting two damaged copies of the gene will be affected by PCH.
Mutations in the genes that cause PCH produce faults in the production of chemicals, usually enzymes, that are required for the development of nerve cells (neurons) and for properly processing RNA, which is needed for any cell to function normally. The exact mechanism by which PCH affects the development of the cerebellum and pons is not well understood.
The severity of different forms of PCH varies, but many children inheriting the mutated gene responsible do not survive infancy or childhood; nevertheless, some individuals born with PCH have reached adulthood.
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- "Pontocerebellar hypoplasia". Genetics Home Reference. U.S. National Library of Medicine. December 2009. Retrieved 20 September 2014.
- Anderson, C; Davies, JH; Lamont, L; Foulds, N (April 2011). "Early pontocerebellar hypoplasia with vanishing testes: A new syndrome?". American Journal of Medical Genetics. Part a 155A (4): 667–72. doi:10.1002/ajmg.a.33897. PMID 21594990.
- Namavar, Y; Barth, PG; Poll-The, BT; Baas, F (2011). "Classification, diagnosis and potential mechanisms in pontocerebellar hypoplasia". Orphanet Journal of Rare Diseases 6: 50. doi:10.1186/1750-1172-6-50. PMC 3159098. PMID 21749694.
- Mukherjee, K; Slawson, JB; Christmann, BL; Griffith, LC (2014). "Neuron-specific protein interactions of Drosophila CASK-β are revealed by mass spectrometry". Frontiers in Molecular Neuroscience 7: 58. doi:10.3389/fnmol.2014.00058. PMC 4075472. PMID 25071438.
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