Transcript Light and Electron Microscopic Studies, Gene Mutation Analysis of

Light and Electron Microscopic Studies,
Gene Mutation Analysis of Case of
Macular Corneal Dystrophy
Department of Ophthalmology, St. Mary’s Hospital,
College of Medicine, The Catholic University of Korea
Sung Kun Chung, MD, PhD, You Kyung Lee, MD, Dong Jin Chang, MD,
The authors have no financial interest in the subject matter of this poster.
Purpose
• To report and describe a novel mutation within the
CHST6 gene via light and electron microscopic study
in a case of macular corneal dystrophy after
penetrating keratoplasty in Korea.
Materials
• Case
– A 59 year-old female
– presented with progressive loss of vision over a period of
50 years.
– family history of macular corneal dystrophy.
– underwent penetrating keratoplasty of the right eye.
• Light microscopy and transmission electron microscopy
were conducted on the removed corneal specimens.
– Hematoxylin and eosin(HE), Alcian blue, periodic acidSchiff (PAS), Colloidal iron, and Masson-Trichrome stains
were performed on the specimen.
• genomic DNA was obtained from peripheral blood
samples.
Materials
The squares indicate males and the circles indicate females.
A shadowing image indicates a person affected with macular corneal
dystrophy.
The arrow indicates the case patient
Results
Comparison between light microscopic appearances (upper line: x100, lower line: x400)
Positive finding for glycosaminoglycan was indicated with arrows (B,C,D).
A, Hematoxylin and Eosin stain. B, Alcian blue stain. C, Colloidal iron stain. D, Periodic
acid-Schiff stain E, Masson-Trichrome stain
Results
Transmission electron microscopic
findings.
A, Keratocyte distended by
membrane-bound intracytoplasmic
vacuoles containing electron dense
fibrillogranular material (black
arrow). Vacuole containing dense
fibrillogranular material in the
interstromal lamellae (white arrow).
Asterisk indicates relatively normal
keratocyte (Scale bar: 2㎛).
B, Keratocyte with vacuoles
containing dense osmiophilic whirls
(Scale bar: 0.5㎛).
Results
Direct sequencing analysis of the coding region of CHST6.
Sequence of the coding region of CHST6 revealed a change
of the nucleotide at codon 205 (CGG→TGG).
This missense mutation has not been previously reported.
Results
Slit lamp photograph of case approximately 1 year after
penetrating keratoplasty shows no complications.
Conclusions
• Macular corneal dystrophy (MCD), an autosomal-recessive
disease, is the least common of the classic stromal dystrophies.
• We describe a case of macular corneal dystrophy with
histopathological findings. We also report a novel missense
mutation within the CHST6 gene (p.Arg205Trp) in Korea.
• The p.Arg205Trp mutation is a new missense mutation which
changes arginine to tryptophan, inducing the substitution of a
neutral amino acid to a basic amino acid. This mutation could
also affect protein function.
Conclusions
• Light microscopy presents abnormal deposits of
glycosaminoglycans in Bowman’s histiocytes, keratocytes,
between the stromal lamellae, Descemet’s membrane, and
endothelium. These glycosaminoglycans stain positively with
Alcian blue, Colloidal iron and periodic acid-Schiff (PAS).
• Electron microscopy revealed that these deposits correspond to
electro-lucent fibrillogranular material visible within membranebound intracytoplasmic vacuoles. Such abnormalities have been
shown to be the sequelae of an error in glycosaminoglycans
metabolism within the cornea, in particular the proteoglycan
keratan sulfate, resulting in its abnormal intra and extracellular
deposition.
Conclusions
• The CHST6 protein is a sulfotransferase, a carbohydrate
sulfotransferase of the semi-methyl-D/N-acetylgalactose/Nacetyl glucosamine-6-O-sulfotransferase family,
which can catalyze the phosphorylation of 6-hydroxy-6-O of Nacetyl glucosamine, galactose, and N-acetyl galactosamine.
• The variations in the coding region of CHST6 may reduce the
activity of the enzyme or cause it to be lost, resulting in a low
sulfated form or non-sulfated form of keratan sulfate. Due to
the loss of its soluble properties, non-sulfated keratan sulfate
cannot be completely metabolized, inducing the deposition of
sediment in the corneal stroma.