Search

Microphthalmia, anophthalmia and coloboma (MAC) are distinct phenotypes that represent a continuum of structural developmental eye defects. In severe bilateral cases (anophthalmia or severe microphthalmia) the genetic cause is now identifiable in approximately 80 percent of cases, with de novo heterozygous loss-of-function mutations in SOX2 or OTX2 being the most common. The genetic cause of other forms of MAC, in particular isolated coloboma, remains unknown in the majority of cases. This review will focus on MAC phenotypes that are associated with mutation of the genes SOX2, OTX2, PAX6, STRA6, ALDH1A3, RARB, VSX2, RAX, FOXE3, BMP4, BMP7, GDF3, GDF6, ABCB6, ATOH7, C12orf57, TENM3 (ODZ3), and VAX1. Recently reported mutation of the SALL2 and YAP1 genes are discussed in brief. Clinical and genetic features were reviewed in a total of 283 unrelated MAC cases or families that were mutation-positive from these 20 genes. Both the relative frequency of mutations in MAC cohort screens and the level of confidence in the assignment of disease-causing status were evaluated for each gene., (Copyright © 2014 Elsevier Masson SAS. All rights reserved.)

Purpose: To investigate whether 173 patients with microphthalmia, anophthalmia, and coloboma have mutations in the eye-development gene SIX6., Methods: The two exons of the SIX6 gene were amplified by PCR from patients' genomic DNA and directly sequenced to search for mutations. The PCR products of 75 patients were also analyzed by denaturing high-performance liquid chromatography (DHPLC)., Results: Six SIX6 polymorphisms were identified in the patient panel. Three of these polymorphisms change the encoded amino acid. However, all six polymorphisms were also identified in unaffected individuals. There was no statistically significant difference in genotypes between patients and control subjects., Conclusions: No evidence was found that SIX6 mutations underlie human congenital structural eye malformations.

Anophthalmia and microphthalmia are important birth defects, but their pathogenesis remains incompletely understood. We studied a patient with severe unilateral microphthalmia who had a 2.7 Mb deletion at chromosome 18q22.1 that was inherited from his mother. In-situ hybridization showed that one of the deleted genes, TMX3, was expressed in the retinal neuroepithelium and lens epithelium in the developing murine eye. We re-sequenced TMX3 in 162 patients with anophthalmia or microphthalmia, and found two missense substitutions in unrelated patients: c.116G>A, predicting p.Arg39Gln, in a male with unilateral microphthalmia and retinal coloboma, and c.322G>A, predicting p.Asp108Asn, in a female with unilateral microphthalmia and severe micrognathia. We used two antisense morpholinos targeted against the zebrafish TMX3 orthologue, zgc:110025, to examine the effects of reduced gene expression in eye development. We noted that the morphant larvae resulting from both morpholinos had significantly smaller eye sizes and reduced labeling with islet-1 antibody directed against retinal ganglion cells at 2 days post fertilization. Co-injection of human wild type TMX3 mRNA rescued the small eye phenotype obtained with both morpholinos, whereas co-injection of human TMX3(p.Arg39Gln) mutant mRNA, analogous to the mutation in the patient with microphthalmia and coloboma, did not rescue the small eye phenotype. Our results show that haploinsufficiency for TMX3 results in a small eye phenotype and represents a novel genetic cause of microphthalmia and coloboma. Future experiments to determine if other thioredoxins are important in eye morphogenesis and to clarify the mechanism of function of TMX3 in eye development are warranted.

We describe a novel recognizable phenotype characterized by anophthalmia, a distinctive skeletal dysplasia and intellectual disability. Radiographic anomalies include severe rhizomelic shortness of the limbs and abnormal joint formation. Recent exome studies showed that these characteristics are part of the phenotypic spectrum of MAB21L2 gene mutations which cause a range of structural eye malformations such as microphthalmia/anophthalmia and ocular coloboma. The two unrelated individuals described here in detail are heterozygous carriers of the same de novo missense mutation c.151C > T (p.Arg51Cys) in MAB21L2. [ABSTRACT FROM AUTHOR]