CRYBB2 gene

Overview

Gene (OMIM No.)
Function of gene/protein
  • Protein: crystallin beta B2
  • Lens-specific protein with structural and functional components
  • Involved in lens development
  • Functions as a molecular chaperone in its oxidised form
Clinical phenotype
(OMIM phenotype no.)
  • Cataract 3, multiple types (#601547)
Inheritance
  • Autosomal dominant
Ocular features
Systemic features
  • No extraocular features have been reported
Key investigations
  • B-scan USS to measure axial length to document microphthalmia and detect any posterior segment abnormalities
  • Electrophysiology
  • TORCH screen
  • MRI brain and orbit
  • Assessment with a paediatrician if suspicious of systemic involvement
Molecular diagnosisNext generation sequencing
  • Targeted gene panels (cataract)
  • Whole exome sequencing
  • Whole genome sequencing
ManagementOcular
Therapies under research
  • None at present
Further information

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Additional information

In the first pedigree of autosomal dominant congenital cerulean cataract reported by Bodker et al and subsequently by Kramer et al, a female (individual #102) who was product of a consanguineous marriage between two affected cousins, displayed congenital cataract, microphthalmia and microcornea.[3,4] All other affected family members only had isolated cataract with mild visual symptoms in their childhood and early adolescence. Individual #102 required cataract extraction at age 5 years and loss her vision later in adulthood due to bilateral band keratopathy and corneal neovascularisation. Litt et al later identified that she harboured a homozygous truncating p.Gln155Ter mutation while the other affected family members were heterozygous, thus representing a rare example of homozygosity for a dominant mutation.[5]

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References

  1.  Bateman JB, von-Bischhoffshaunsen FR, Richter L, Flodman P, Burch D, Spence MA. Gene conversion mutation in crystallin, beta-B2 (CRYBB2) in a Chilean family with autosomal dominant cataract. Ophthalmology. 2007;114(3):425‐432
  2.  Bijlsma EK, Delattre O, Juyn JA, et al. Regional fine mapping of the beta crystallin genes on chromosome 22 excludes these genes as physically linked markers for neurofibromatosis type 2. Genes Chromosomes Cancer. 1993;8(2):112‐118
  3.  Bodker FS, Lavery MA, Mitchell TN, Lovrien EW, Maumenee IH. Microphthalmos in the presumed homozygous offspring of a first cousin marriage and linkage analysis of a locus in a family with autosomal dominant cerulean congenital cataracts. Am J Med Genet. 1990;37(1):54‐59
  4.  Kramer P, Yount J, Mitchell T, et al. A second gene for cerulean cataracts maps to the beta crystallin region on chromosome 22. Genomics. 1996;35(3):539‐542
  5.  Litt M, Carrero-Valenzuela R, LaMorticella DM, et al. Autosomal dominant cerulean cataract is associated with a chain termination mutation in the human beta-crystallin gene CRYBB2. Hum Mol Genet. 1997;6(5):665‐668
  6.  Gill D, Klose R, Munier FL, et al. Genetic heterogeneity of the Coppock-like cataract: a mutation in CRYBB2 on chromosome 22q11.2. Invest Ophthalmol Vis Sci. 2000;41(1):159‐165
  7.  Kerscher S, Church RL, Boyd Y, Lyon MF. Mapping of four mouse genes encoding eye lens-specific structural, gap junction, and integral membrane proteins: Cryba1 (crystallin beta A3/A1), Crybb2 (crystallin beta B2), Gja8 (MP70), and Lim2 (MP19). Genomics. 1995;29(2):445‐450

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Updated on November 30, 2020
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