Deletions in PITX1 cause a spectrum of lower-limb malformations including mirror-image polydactyly

Abstract

PITX1 is a bicoid-related homeodomain transcription factor implicated in vertebrate hindlimb development. Recently, mutations in PITX1 have been associated with autosomal-dominant clubfoot. In addition, one affected individual showed a polydactyly and right-sided tibial hemimelia. We now report on PITX1 deletions in two fetuses with a high-degree polydactyly, that is, mirror-image polydactyly. Analysis of DNA from additional individuals with isolated lower-limb malformations and higher-degree polydactyly identified a third individual with long-bone deficiency and preaxial polydactyly harboring a heterozygous 35 bp deletion in PITX1. The findings demonstrate that mutations in PITX1 can cause a broad spectrum of isolated lower-limb malformations including clubfoot, deficiency of long bones, and mirror-image polydactyly.

Figure 1

Haploinsufficiency of PITX1 causes variable lower-limb malformations. Case 1: Reconstructions of postmortem CT scans, as well as clinical pictures showing the pes equinovarus configuration and mirror-image polydactyly. Whole body CT reconstruction shows normal upper limb and axial skeleton. FISH analysis indicating a deletion on 5q31 (arrow; green=control probe, red=locus specific probe). Case2: Ultrasound examination in a fetus in the 15th gestational week shows polydactyly and long-bone deficiency. Case 3: Note long-bone deficiency, preaxial polydactyly as well as bilateral clubfoot. The right side is more severely affected (absent tibia) than the left. Molecular genetic testing of PITX1 showed a second faster migrating amplicon of exon 3 by gel electrophoresis of the DNA from the affected individual (pat) in comparison with the maternal amplicon (co). Direct sequencing revealed a deletion of 35 bases (c.765_799del). The electropherograms show the respective genomic sequence of exon 3 (upper panel) as well as a subcloned mutated allele (lower panel) from the patient. The breakpoint is indicated by a dashed line. PITX1 is composed of three exons (E1-E3, NM_002653.4, coding region in blue). Case 1 and case 2 showed larger interstitial genomic deletions on chromosome 5 including PITX1 as determined by array CGH. The location and size of the three deletions is visualized by red bars and is given according to NCBI36/hg18.