Common MFRP sequence variants are not associated with moderate to high hyperopia, isolated microphthalmia, and high myopia.
OBJECTIVE
The membrane-type frizzled-related protein (MFRP) gene is selectively expressed in the retinal pigment epithelium and ciliary body, and mutations of this gene cause nanophthalmos. The MFRP gene may not be essential for retinal function but has been hypothesized to play a role in ocular axial length regulation. The involvement of the MFRP gene in moderate to high hyperopic, isolated microphthalmic/anophthalmic, and high myopic patients was tested in two phases: a mutation screening/sequence variant discovery phase and a genetic association study phase.


METHODS
Eleven hyperopic, ten microphthalmic/anophthalmic, and seven non-syndromic high-grade myopic patients of varying ages and 11 control subjects participated in the mutation screening phase. Sixteen primer pairs were designed to amplify the 13 exons of the MFRP gene including intron/exon boundaries. Polymerase chain reactions were performed, and amplified products were sequenced using standard techniques. Normal and affected individual DNA sequences were compared alongside the known reference sequence (UCSC genome browser) for the MFRP gene. The genetic association study included 146 multiplex non-syndromic high-grade myopia families. Seventeen intragenic and flanking single nucleotide polymorphisms (SNPs) were chosen for the MFRP gene and genotyped in the large data set using the Taqman allelic discrimination assay. The family-based association Pedigree Disequilibrium Test (PDT) and GenoPDT were performed.


RESULTS
The average spherical refractive error of the hyperopic patient cohort was +4.21 diopters (D; range +2.00 to +9.25 D) and of the myopic patient cohort was -12.36 D (range -8.25 to -14.50 D). A total of 16 SNPs were identified by direct sequencing. No significant association was determined between the 16 MFRP gene SNPs and the moderate to high hyperopia, microphthalmia/anophthalmia affection status, and high myopia. Family based association analysis did not reveal any association between the 17 SNPs genotyped in the larger family data set for any refractive error type.


CONCLUSIONS
Sequence variants of the MFRP gene do not appear to be associated with either the less severe forms of hyperopia, extreme forms of limited eye growth and development, or high myopia. These results indicate that the MFRP gene may not play a role in regulating ocular axial length in these phenotypes.
Metlapally
Ravikanth
R
Duke University Eye Center, Durham, NC, USA.
Li
Yi-Ju
YJ
Tran-Viet
Khanh-Nhat
KN
Bulusu
Anuradha
A
White
Tristan R
TR
Ellis
Jaclyn
J
Kao
Daniel
D
Young
Terri L
TL
D001483:Base Sequence; D002880:Chromosomes, Human, Pair 11 / Q000235:genetics; D004252:DNA Mutational Analysis; D005091:Exons / Q000235:genetics; D005190:Family; D020022:Genetic Predisposition to Disease; D006801:Humans; D006956:Hyperopia / Q000235:genetics*; D015810:Linkage Disequilibrium / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics*; D008850:Microphthalmos / Q000235:genetics*; D009154:Mutation / Q000235:genetics*; D009216:Myopia / Q000235:genetics*; D010641:Phenotype; D012031:Refractometry; D000099274:Frizzled-Related Proteins
D008565:Membrane Proteins; C490110:MFRP protein, human; D000099274:Frizzled-Related Proteins