Only five unique PITX3 mutations have been described, of which the 17-bp duplication c.640_656dup, p.(Gly220Profs*95), is the most common one and the only one known to cause cataract with ASD.
The results show that in some individuals within one family, duplication of this segment of PITX3 can result in severe symptoms leading to functional blindness while in other individuals in the same family or in other families, the same duplication leads to treatable cataract with minimal visual impairment.
The 657ins17bp duplication of the PITX3 gene is the cause of the cataract phenotype in the large pedigree, however, this gene appears responsible for only a small proportion of congenital cataract in Australia.
The PITX3 gene, which codes for a homeobox bicoidlike transcription factor is responsible for dominant cataract and anterior segment mesenchymal dysgenesis in humans.
Although the same genotype was described in a family with ASMD and cataracts, the common phenotype of this mutation is probably posterior polar cataract; a modifier gene is presumed to cause anterior segment abnormalities in the previously described patients.
Mutations in the homologous human PITX3 gene have been demonstrated to be causative of cataracts and the dysmorphology of the anterior segment of the eye.