Unusual patterns of inheritance were also observed when comparing genotype-wise associations in children versus mothers suggesting that there may be a direct effect of mother��s genotype, or that there may be parent-of-origin effects, i.e. that for the child it is the origin of, and not just the combination of, alleles that is important in determining disease risk. Using a log-linear method previously designed to evaluate maternal genotype and/or parent-of-origin effects in case-parent trios. The isoform without exon 10 has not been previously reported. Since there is no expressed sequence tag cDNA or RNA evidence for this spliced variant reported in the ENSEMBL genome database, we cannot be certain that this transcript is translated into a functional protein. For the known functional exon 10-containing isoform at ABCA4 we found that 4 of the 5 EBV lines that were heterozygous for genomic DNA showed monoallelic Epimedoside-A expression in cDNA for the exon 10 Yunaconitine rs3112831 SNP. This mono-allelic expression was observed independently in multiple RNA extractions from each of which multiple cDNA preparations were made from these EBV cell lines, demonstrating that this was not due to chance events in amplification of the cDNA. Examining parental genotypes in the EBV cell bank, we determined that the paternally-derived allele is silenced for the exon10-containing isoform of ABCA4. However, given the small sample of polyclonal EBV cell lines examined we cannot state definitively that it is always the paternally-derived allele that is silenced. Hence, this could represent random choice autosomal monoallelic expression, which has recently been shown to be more common in the genome than was previously supposed. This could also account for the apparent polymorphic nature of the silencing, since a majority of genes showing random choice autosomal monoallelic expression display biallelic expression in some clonal cell lines. Since all the EBV cell lines employed here were polyclonal, imprinting currently provides the more likely explanation for the monoallelic expression we observed. We also demonstrated monoallelic expression for a SNP in exon 7 in cDNA specifically amplified for the IIB short form of COL2A1, but not for cDNA amplified for the IIA long form, consistent with isoform-specific imprinting in this case with the maternally-derived allele silenced. This fits with the observation that COL2A1 lies within a cluster of genes on human chromosome 12q13.11 syntenic with mouse chromosome 15 band F2 that are known to be maternally imprinted, although again we cannot definitively exclude autosomal random mono-allelic expression. Herein we examined the specific genetic hypothesis that 
polymorphisms in two genes known to be associated with ocular disease, ABCA4 and COL2A1, are associated with ocular disease caused by congenital toxoplasmosis. Evidence for genetic associations observed initially in a European cohort was replicated in an independently ascertained cohort from North America. One value of genetic association studies is that they provide concrete insight into processes that determine clinical outcome of disease, in this case events that may occur in embryonic development when it is not easy to determine what is happening when the fetus is infected with a parasite such as T. gondii, or what the parasite is doing during early post-natal development. We chose to look specifically for associations with ABCA4 and COL2A1 because both had defined single gene disorders that result in congenital or early onset ocular disease.