Medicine:Temple–Baraitser syndrome

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Temple–Baraitser syndrome
Other namesSevere mental retardation and absent nails of hallux and pollex
Temple Baraitser Hand.jpg
Small fingernails typical of Temple–Baraitser syndrome.
CausesGain of function variants in KCNH1
Differential diagnosisZimmermann–Laband syndrome
DOOR syndrome
Frequencyunknown

Temple–Baraitser syndrome (TBS) is a very rare autosomal dominant genetic disorder, characterised by intellectual disability, epilepsy, small or absent nail of the thumbs and great toes, and distinct craniofacial features.[1]

Genetics

TBS is caused by pathogenic variants (mutations) in the KCNH1 gene at chromosomal locus 1q32.2, (GRCh38): 1:210,678,313-211,134,147.[2] It has an autosomal dominant transmission, however affected individuals are not known to reproduce, so all reported cases have been caused by de novo mutations or transmission from a mosaic parent.[3]

Diagnosis

Temple–Baraitser syndrome is diagnosed by clinical examination of a person with a severe developmental disability, intellectual impairment and epilepsy. The face is often long and myopathic. Overgrown gums become apparent in late childhood. The finger and toenails are characteristically small, with complete or almost complete absence of the nails of the thumb (pollex) and great toe (hallux).[4][5] The diagnosis can be confirmed by demonstrating a gain-of-function mutation in the KCNH1 gene.[6] Temple–Baraitser has clinical and genetic overlap with type 1 Zimmermann–Laband syndrome.[7]

Management

Affected individuals should see a pediatrician or adult physician at least annually to monitor growth, development, seizures and general health and well-being. Developmental potential is maximized through the use of physiotherapy, occupational therapy and speech pathology. Anticonvulsants are used to control epilepsy.[8]

Prevalence

With fewer than 100 cases having been reported worldwide, the exact prevalence is unknown but is believed to be rare. It is likely to be underdiagnosed, with one large study identifying 2.7% of people with intellectual disability to have a mutation in KCNH1.[9]

Etymology

The syndrome's named was coined by Michael Gabbett who named it after English clinical geneticists Karen Temple and Michael Baraitser.[10][11] Temple and Baraitser described the first case in 1991.[12][13]

References

  1. ↑ Vilain, C. "Temple-Baraitser syndrome". Orphanet. https://rarediseases.info.nih.gov/diseases/9441/temple-baraitser-syndrome. 
  2. ↑ Simons, Cas; Rash, Lachlan D.; Crawford, Joanna; Ma, Linlin; Cristofori-Armstrong, Ben; Miller, David; Ru, Kelin; Baillie, Gregory J. et al. (January 2015). "Mutations in the voltage-gated potassium channel gene KCNH1 cause Temple–Baraitser syndrome and epilepsy" (in en). Nature Genetics 47 (1): 73–77. doi:10.1038/ng.3153. ISSN 1061-4036. PMID 25420144. 
  3. ↑ Genetic Services Laboratory. "Temple–Baraitser syndrome testing: Mutation analysis of KCNH1". University of Chicago. https://dnatesting.uchicago.edu/sites/default/files/media/documents/Temple-Baraitser%20%28KCNH1%29%20Infosheet%206-20-19.pdf. 
  4. ↑ Jacquinet, Adeline; Gérard, Marion; Gabbett, Michael T.; Rausin, Léon; Misson, Jean-Paul; Menten, Bjorn; Mortier, Geert; van Maldergem, Lionel et al. (2010). "Temple–Baraitser Syndrome: A Rare and Possibly Unrecognized Condition". Am J Med Genet A 152A (9): 2322–2326. doi:10.1002/ajmg.a.33574. PMID 20683999. https://doi.org/10.1002/ajmg.a.33574. 
  5. ↑ McLaren, H. "Temple-Baraitser syndrome". OLS. http://www.ebi.ac.uk/efo/EFO_0009062. 
  6. ↑ Gabbett, Michael T.. "KCNH1 - Molecular Characteristics". Human Disease Genes. https://humandiseasegenes.nl/kcnh1/professionals/molecular-characteristics. 
  7. ↑ Bramswig, Nuria C; Ockeloen, CW; Czeschik, JC; vanEssen, AJ; Pfundt, R; Smeitink, J; Poll-The, BT; Engels, H et al. (2015). "'Splitting versus lumping': Temple-Baraitser and Zimmermann-Laband Syndromes". Hum Genet 134 (10): 1089–97. doi:10.1007/s00439-015-1590-1. PMID 26264464. http://doi.org/10.1007/s00439-015-1590-1. 
  8. ↑ Gabbett, Michael T.. "KCNH1 Management". Human Disease Genes. https://humandiseasegenes.nl/kcnh1/professionals/management. 
  9. ↑ Bramswig, NC; Ockeloen, CW; Czeschik, JC; van Essen, AJ; Pfundt, R; Smeitink, J; Poll-The, BT; Engels, H et al. (2015). "Splitting versus lumping': Temple–Baraitser and Zimmermann–Laband Syndromes". Hum Genet 134 (10): 1089–1097. doi:10.1007/s00439-015-1590-1. PMID 26264464. https://doi.org/10.1007/s00439-015-1590-1. 
  10. ↑ Ward, Gemma (25 November 2014). "Genetic test unlocks cause of Brisbane boy's rare disease". The University of Queensland. https://imb.uq.edu.au/genetic-test-unlocks-rare-disease. 
  11. ↑ Pash, Chris. "This Brisbane Boy Is Just One Of Seven People In The World With A Rare Condition". Pedestrian Group. https://www.thechainsaw.com/this-brisbane-boy-is-just-one-of-seven-people-in-the-world-with-a-rare-condition-2014-11. 
  12. ↑ Gabbett, Michael T.; Clark, Ronald C; McGaughran, Julie M (2008). "A Second Case of Severe Mental Retardation and Absent Nails of Hallux and Pollex (Temple–Baraitser Syndrome)". American Journal of Medical Genetics Part A 146A (4): 450–452. doi:10.1002/ajmg.a.32129. PMID 18203178. https://doi.org/10.1002/ajmg.a.32129. 
  13. ↑ Temple, Karen I; Baraitser, Michael (1991). "Severe mental retardation and absent nails of hallux and pollex". Am J Med Genet 41 (2): 173–175. doi:10.1002/ajmg.1320410207. PMID 1785628. https://doi.org/10.1002/ajmg.1320410207. 

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