Posterior microphthalmia (PM) is a relatively rare autosomal recessive condition with normal anterior segment and small posterior
segment resulting in high hyperopia and retinal folding. It is an uncommon subtype of microphthalmia that has been mostly
reported to coexist with several other ophthalmic conditions and to occur in sporadic cases. The membrane-type frizzled-related
protein (
MFRP) is the only gene so far reported implicated in autosomal recessive, non-syndromic and syndromic forms of PM. Here, we performed
a clinical and genetic analysis using six consanguineous families ascertained from different regions of Tunisia and affected
with non-syndromic PM that segregates as an autosomal recessive trait. To identify the disease-causing defect in these families,
we first analysed
MFRP gene, then some candidate genes (
CHX10,
OPA1,
MITF,
SOX2,
CRYBB1-3 and
CRYBA4) and loci (MCOP1, NNO1 and NNO2) previously implicated in different forms of microphthalmia. After exclusion of these genes
and loci, we performed a genome-wide scan using a high density single nucleotide polymorphism (SNP) array 50 K in a large
consanguineous pedigree. SNP genotyping revealed eight homozygous candidate regions on chromosomes 1, 2, 3, 6, 15, 17 and
21. Linkage analysis with additional microsatellite markers only retained the 2q37.1 region with a maximum LOD score of 8.85
obtained for D2S2344 at θ = 0.00. Further investigations are compatible for linkage of four more families to this region with
a refined critical interval of 2.35 Mb. The screening of five candidate genes
SAG,
PDE6D,
CHRND,
CHRNG and
IRK13 did not reveal any disease-causing mutation.