Focus on molecules: Pitx3

The molecular genetics of anterior segment dysgenesis

Anterior segment dysgenesis is a severe developmental eye disorder that leads to blindness in children. The exact mechanisms underlying this condition remain elusive. Recently, an increasing amount of studies have focused on genes and signal transduction pathways that affect anterior segment dysgenesis;these factors include transcription factors, developmental regulators, extracellular matrix genes, membrane-related proteins, cytoskeleton proteins and other associated genes. To date, dozens of gene variants have been found to cause anterior segment dysgenesis. However, there is still a lack of effective treatments. With a broader and deeper understanding of the molecular mechanisms underlying anterior segment development in the future, gene editing technology and stem cell technology may be new treatments for anterior segment dysgenesis. Further studies on the mechanisms of how different genes influence the onset and progression of anterior segment dysgenesis are still needed.

Investigating the Clinical Characteristics and PITX3Mutations of a Large Chinese Family with Anterior Segment Mesenchymal Dysgenesis and Congenital Posterior Polar Cataract

Objective

To investigate the clinical characteristics and pathogenic genetic mutations of a Chinese family with anterior segment mesenchymal dysgenesis and congenital posterior polar cataract.

Methods

Through family investigation, the family members were examined via slit lamp anterior segment imaging and screened for eye and other diseases by eye B-ultrasound. Genetic test was performed on the blood samples of the fourth family generation (23 people) via whole exome sequencing (trio-WES) and Sanger sequencing.

Results

Among the 36 members in four family generations, there were 11 living cases with different degrees of ocular abnormalities, such as cataracts, leukoplakia, and small cornea. All patients who received the genetic test had the heterozygous frameshift mutation c.640_656dup (p.G220Pfs∗95) on exon 4 of the PITX3 gene. This mutation was cosegregated with the clinical phenotypes in the family and thus might be one of the genetic factors that cause the corresponding ocular abnormalities in this family.

Conclusion

The congenital posterior polar cataract with or without anterior interstitial dysplasia (ASMD) of this family was inherited in an autosomal dominant manner, and the frameshift mutation (c.640_656dup) in the PITX3 gene was the cause of ocular abnormalities observed in this family. This study is of great significance for guiding prenatal diagnosis and disease treatment.

Conserved genetic pathways associated with microphthalmia, anophthalmia, and coloboma

The human eye is a complex organ whose development requires extraordinary coordination of developmental processes. The conservation of ocular developmental steps in vertebrates suggests possible common genetic mechanisms. Genetic diseases involving the eye represent a leading cause of blindness in children and adults. During the last decades, there has been an exponential increase in genetic studies of ocular disorders. In this review, we summarize current success in identification of genes responsible for microphthalmia, anophthalmia, and coloboma (MAC) phenotypes, which are associated with early defects in embryonic eye development. Studies in animal models for the orthologous genes identified overlapping phenotypes for most factors, confirming the conservation of their function in vertebrate development. These animal models allow for further investigation of the mechanisms of MAC, integration of various identified genes into common developmental pathways and finally, provide an avenue for the development and testing of therapeutic interventions.

Genetics of anterior segment dysgenesis disorders

PURPOSE OF REVIEW

Anterior segment dysgenesis (ASD) disorders encompass a spectrum of developmental conditions affecting the cornea, iris, and lens and are generally associated with an approximate 50% risk for glaucoma. These conditions are characterized by both autosomal dominant and recessive patterns of inheritance often with incomplete penetrance/variable expressivity. This article summarizes what is known about the genetics of ASD disorders and reviews recent developments.

RECENT FINDINGS

Mutations in Collagen type IV alpha-1 (COL4A1) and Beta-1,3-galactosyltransferase-like (B3GALTL) have been reported in ASD patients. Novel findings in other well known ocular genes are also presented, among which regulatory region deletions in PAX6 and PITX2 are most notable.

SUMMARY

Although a number of genetic causes have been identified, many ASD conditions are still awaiting genetic elucidation. The majority of characterized ASD genes encode transcription factors; several other genes represent extracellular matrix-related proteins. All of the involved genes play active roles in ocular development and demonstrate conserved functions across species. The use of novel technologies, such as whole genome sequencing/comparative genomic hybridization, is likely to broaden the mutation spectrums in known genes and assist in the identification of novel causative genes as well as modifiers explaining the phenotypic variability of ASD conditions.