Keratocan

Alternative Names

  • KERA

Associated Diseases

Cornea Plana 2
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OMIM Number

603288

Gene Map Locus
12q21.33

Description

The core protein of a major corneal keratan sulfate proteoglycan is encoded by the KERA gene, located on chromosome 12q21.33.  KERA is expressed mainly in the cornea and sclera, and it is also expressed, at lower levels, in the skin, ligaments, cartilage, arteries, and striated muscles.  Keratan sulfate proteoglycan protein may play an important role in developing and maintaining corneal transparency and in forming the structure of the stromal matrix.

Molecular Genetics

The KERA gene spans approximately 7.9 kb of genomic DNA, and encodes a protein of 352 amino acids and weights 405.09 kDa.  The gene consists of three exons.  Exon 1 is untranslated while exon 2 contains the start codon and an N-terminal signal peptide followed by a highly conserved region containing 10 leucine-rich repeat (LRR) motifs.  Mutations in this gene are the cause of autosomal cornea plana type 2.

Epidemiology in the Arab World

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Other Reports

Saudi Arabia

Khan et al. (2004) performed PCR and direct DNA sequencing for the three exons and exon-intron boundaries of the KERA gene in an Arab family of first cousin parents with six children, five of whom were affected with cornea plana.  A novel homozygous (937C>T) nonsense mutation was identified within exon 3 in the five affected children.  This mutation changed the amino acid arginine to a premature termination codon at position 313 (p.R131X).  The resulting truncated protein had 312 amino acids instead of the normal 352 amino acids and does not have the highly conserved eleventh LRR motif of normal keratocan.  Both parents were heterozygous for the mutation, which was absent in the clinically unaffected brother.  In a second study, Khan et al. (2005) described 12 individuals from a Saudi nuclear family with autosomal recessive cornea plana.  All family members underwent KERA DNA sequencing.  A novel mutation was detected in exon 2 (c.1454 C>T) changing an arginine amino acid at position 279 to a stop codon (p.R279X).  The resultant truncated protein lacks the terminal 73 amino acids of normal keratocan. This mutation was homozygous in five siblings with clinically evident cornea plana and a sister with clinical findings of pellucid marginal degeneration and cornea plana.  All other family members were heterozygous for the mutation and clinically unaffected.

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