Hereditary lattice corneal dystrophy is associated with corneal amyloid deposits enclosing C-terminal fragments of keratoepithelin.
OBJECTIVE
To investigate the molecular basis of hereditary lattice corneal dystrophy (LCD) type IIIA associated with corneal amyloid deposits afflicting several members of a four-generation family.


METHODS
Histologic, immunohistochemical and biochemical studies were performed on corneal tissue samples obtained after perforating keratoplasty. DNA was extracted from peripheral blood leukocytes. All exons of the keratoepithelin-encoding TGFBI gene were amplified and sequenced. The presence of a mutation was confirmed by digestion of the isolated PCR product with the restriction enzyme AlwNI.


RESULTS
The cornea of the index patient (II-1) contained large patchy deposits of amyloid, which were immunoreactive for the C terminus of keratoepithelin. Western blot analysis of the polypeptide chains extracted from the amyloid deposits of paraffin-embedded tissue revealed that these represented mainly fragments of the full-length protein. The smallest fragments were 6.5 and 6.9 kDa. DNA analyses of the TGFBI gene revealed a heterozygous T-->C transition at the second position of codon 540 in exon 12, indicating that replacement of phenylalanine by serine (Phe540Ser) leads to dominant disease. The mutation creates a new restriction site for the enzyme AlwNI. Five of the examined family members carried this mutation. Three of them (aged >/=41 years) had the disease, two family members (aged <20 years) do not yet show any clinical symptoms. An additional inconsequential single-nucleotide polymorphism (T1667C) was found at the third position of the same codon (Phe540Phe) in three unaffected family members.


CONCLUSIONS
This is the first report of a single-nucleotide mutation at codon 540 of TGFBI leading to LCD, and the first to demonstrate that the amyloid deposits in LCD contain proteolytic fragments of keratoepithelin.
Stix
Barbara
B
Institute of Pathology, Otto-von-Guericke University, Magdeburg, Germany.
Leber
Martina
M
Bingemer
Peter
P
Gross
Christof
C
Rüschoff
Josef
J
Fändrich
Marcus
M
Schorderet
Daniel F
DF
Vorwerk
Christian K
CK
Zacharias
Martin
M
Roessner
Albert
A
Röcken
Christoph
C
D000328:Adult; D000682:Amyloid / Q000378:metabolism*; D028226:Amyloidosis, Familial / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D015153:Blotting, Western; D003062:Codon; D003315:Cornea / Q000378:metabolism* / Q000473:pathology; D003317:Corneal Dystrophies, Hereditary / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D004591:Electrophoresis, Polyacrylamide Gel; D005091:Exons; D016326:Extracellular Matrix Proteins / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005784:Gene Amplification; D006801:Humans; D015948:Keratoplasty, Penetrating; D008297:Male; D008875:Middle Aged; D010375:Pedigree; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D016212:Transforming Growth Factor beta / Q000235:genetics* / Q000378:metabolism; D000099222:betaIG-H3 Protein
D000682:Amyloid; D003062:Codon; D016326:Extracellular Matrix Proteins; D016212:Transforming Growth Factor beta; D000099222:betaIG-H3 Protein