Possible explanations for the observed patterns of association between COL2A1 and clinical signs in congenital toxoplasmosis are (a) that the etiological variant only influences expression or function of the non-silenced exon 2-containing IIA long-form allele; or (b) the disease-causing variant is common to both isoforms but does not manifest as skeletal abnormalities due to the silencing of isoform IIB expressed in cartilage. This evidence concerns the gene COL2A1 and congenital toxoplasmosis.