Anterior segment mesenchymal dysgenesis in a large Australian family is associated with the recurrent 17 bp duplication in PITX3

Abstract

Purpose: A recurrent 17 bp duplication (c.657ins17bp) of a segment of the paired-like homeodomain transcription factor 3 (PITX3) gene on human chromosome 10 has been reported in seven families with autosomal dominant posterior polar cataracts with or without anterior segment mesenchymal dysgenesis (ASMD). ASMD can include Peters anomaly with corneal clouding, iridolenticular corneal adhesions, displaced Schwalbe's line, and cataract as described previously in a large Australian family. This study reports the examination of PITX3 in this Australian family.

Methods: Clinical examinations of the proband and her relatives were performed as part of routine follow up. A polymerase chain reaction (PCR) based test for the duplication in PITX3 was developed, and DNA from 21 members of the proband's family was tested.

Results: All clinically affected members of the family had the same 17 bp duplication of PITX3. There was no difference in the size of the duplication between the severely affected individuals and the more mildly affected individuals. Prenatal diagnosis was performed for two offspring of one affected person. In the first pregnancy, the fetus was shown to carry the duplication while in the second pregnancy, the fetus was shown to be homozygous for the normal allele.

Conclusions: 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.

Figure 1

Pedigree of the anterior segment mesenchymal dysgenesis family. Clinical details are available in the previous paper [3]. Clinical details for IV-9 who has been born since that publication are presented in Methods. Grey symbols indicate individuals with cataract only, and black symbols indicate family members with cataract and additional anterior segment eye abnormalities. The proband, IV-2, is indicated with an arrow.

Figure 2

Proband, IV-2, at the age of 12 years and 6 months. A shows the severely affected right eye with peripheral sclerocornea. B shows the mildly affected left eye, with peripheral corneal  stromal opacity and displaced Schwalbe's line. C shows the proband's eyes without (upper) and with (lower) a colored contact lens in the right eye to mask the corneal opacity.

Figure 3

Sequence of exon 4 of PITX3. Primers are shown in bold. The 11 bp repeated sequence is underlined, and the 17 bp duplication within this block is enclosed in square brackets. The sequence terminates at the TGA stop codon.

Figure 4

Analysis of exon 4 of PITX3.  A: The gel of amplification products is shown. The 231 bp band containing the insertion is clearly separated from the 214 bp band. A heteroduplex band can also be seen in heterozygous individuals. –ve stands for the unaffected, control individual. M stands for the molecular weight marker, a HpaII digest of the plasmid pUC19. The bands either side of the amplification products are 190 and 242 bp. The heteroduplex runs with the 331 bp band. B: The sequence of exon 4, containing the insertion, for individual III-5 is shown.

Figure 5

Prenatal diagnosis of the inherited duplication. Gels of amplification products are shown. Lanes 1 and 6 are a negative control. Lanes 2 and 5 are the positive control, III-5. Lanes 3 and 4 show two dilutions of the CVS material for IV-9. Lanes 7 and 8 show two dilutions of the CVS material for IV-10. M is the molecular weight marker, a HpaII digest of pUC19. IV-9 has the insertion band and IV-10 has only the normal band.