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. 2000 May;84(5):527–530. doi: 10.1136/bjo.84.5.527

A novel keratin 12 mutation in a German kindred with Meesmann's corneal dystrophy

L Corden 1, O Swensson 1, B Swensson 1, R Rochels 1, B Wannke 1, H Thiel 1, W McLean 1
PMCID: PMC1723457  PMID: 10781519

Abstract

AIM—To study a kindred with Meesmann's corneal dystrophy (MCD) to determine if a mutation within the cornea specific K3 or K12 genes is responsible for the disease phenotype.
METHODS—Slit lamp examination of the cornea in four members of the kindred was carried out to confirm the diagnosis of MCD. The region encoding the helix initiation motif (HIM) of the K12 polypeptide was polymerase chain reaction (PCR) amplified from genomic DNA derived from affected individuals in the kindred. PCR products generated were subjected to direct automated sequencing. Restriction enzyme analysis employing Ban I was used to confirm the presence of the mutation in affected individuals of the family.
RESULTS—Sequencing of the K12 gene in an affected individual from the family revealed a novel heterozygous missense mutation (413A→C), predicting the substitution of a proline for a glutamine at codon 130 (Q130P) in the HIM of the K12 protein. The mutation was excluded from 50 normal, unaffected individuals by restriction enyzme analysis and was therefore unlikely to be a common polymorphism.
CONCLUSION—A novel missense mutation in the K12 gene leads to MCD in a German kindred. Missense mutations have now been identified within the region encoding the helix initiation motif of the K12 protein in eight of 11 MCD kindreds analysed at the molecular level.



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Figure 1  .

Figure 1  

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Pedigree of the kindred studied, displaying typical autosomal dominant inheritance. Family members from whom DNA was obtained are marked with an asterisk. Arrow indicates the proband.

Figure 2  .

Figure 2  

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Corneal changes in two patients in the family studied as shown by (a) retroillumination and (b) slit lamp examination. (a) Right eye of individual II-1 (see Fig 1), showing relatively even distribution of microcysts (black arrowheads). Grey lines in the corneal epithelium were also seen in this patient by slit lamp analysis (not shown). This phenomenon is not readily observed by retroillumination. (b) Left eye of individual III-4 (see Fig 1), showing intraepithelial blebs and an irregularly shaped area devoid of microcysts (white arrowhead). The underlying mechanism producing this area of phenotypic reversion is unknown.

Figure 3  .

Figure 3  

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Automated sequencing of K12e1.L/K12e.R PCR products derived from the proband (III-4) and an unaffected individual (II-2) from the kindred, codons 128-132 of K12 shown. (A) In the proband, CAA is replaced by CCA (413A→C) in one allele, predicted to lead to the substitution of a proline residue instead of the normal glutamine at codon 130 (Q130P). (B) Sequence derived from a normal, unaffected individual (II-2) revealing the nucleotide sequence in the region of codon 130, located within the helix initiation motif of the K12 protein. CAA encodes a glutamine at this position. (C) Ban I restriction enzyme digestion of PCR products spanning the mutant region. Through use of a mismatch primer, a Ban I restriction enzyme site is generated within the mutant product. Upon digestion, the 164 bp full sized product is cut into bands of 144 bp and 20 bp (the latter does not resolve on 3% agarose gel). DNA molecular weight markers are shown on the left, with bands at 2000 bp, 1500 bp, 1000 bp, 700 bp, 525 bp, 500 bp, 400 bp, 300 bp, 200 bp, 100 bp, and 50 bp (Cambio, Cambridge).

Figure 4  .

Figure 4  

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Model of the protein structure of the type I keratin, K12 and the type II keratin, K3, revealing the positions of published MCD mutations to January 2000. The α helical rod domain is composed of four subdomains termed 1A, 1B, 2A, and 2B. These subdomains are separated by non-α helical regions, the linkers L1, L12, and L2. The areas in red at the ends of the rod domain are regions of high sequence conservation, the helix initiation and termination motifs, which are critical in filament assembly. Only one mutation has been found within the K3 gene (E509K), in the region encoding the helix termination motif.4 There are two mutations within the region encoding the helix termination motif of the K12 protein; Y429D5 and I426V.23 The remaining mutations are all found within the helix initiation motif of the K12 protein, with mutation of arginine-135 found in four kindreds.4 5 24

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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