A novel, non-stop mutation in FOXE3 causes an autosomal dominant form of variable anterior segment dysgenesis including Peters anomaly

Abstract

Anterior segment dysgenesis (ASD) is a spectrum of disorders that affect the anterior ocular chamber. Clinical studies on a Newfoundland family over the past 30 years show that 11 relatives have a variable ocular phenotype ranging from microcornea to Peters anomaly, segregating as an autosomal dominant trait. To determine the molecular etiology of the variable ASD in this family, we sequenced nine functional candidate genes and identified 44 variants. A point mutation in FOXE3, which codes for a transcription factor involved in the formation of the lens and surrounding structures, co-segregated with the variable ocular phenotype. This novel mutation (c.959G>T) substitutes the stop codon for a leucine residue, predicting the addition of 72 amino acids to the C-terminus of FOXE3. Two recent reports have also identified non-stop mutations in FOXE3 in patients with variable ocular phenotypes and predict an extended protein. Although FOXE3 is a lens-specific gene, we successfully isolated complementary DNA from lymphoblasts of an affected family member, and our sequencing results show that the c.959T allele is absent, suggesting that it may be degraded at the RNA level. Though preliminary, our results challenge the notion that an extended FOXE3 protein causes ASD, and instead suggests a mechanism of haploinsufficiency in the case of non-stop mutations. This study adds to several reports that suggest that autosomal-dominant mutations within FOXE3 cause ASD and has important clinical utility, especially for the diagnosis of mildly affected patients.

Figure 1

A four generation Newfoundland family segregating an autosomal dominant form of anterior segment dysgenesis. The proband (PID III-6: arrow) has congenital Peters anomaly.

Figure 2

Eye phenotype of the proband (PID III-6) over time. (a) Picture of the proband's right eye at 7 weeks showing corneal opacities consistent with Peters anomaly. (b) Surgical drawing of the proband's left eye showing keratolenticular adhesion, and corneal leukoma (pictures a and b are taken from Green and Johnson with permission. (c) Proband's right eye at 30 years of age. (d) Proband's phthisical left eye at 30 years of age.

Figure 3

(a) Agarose gel (1%) stained with SYBR Safe showing PCR amplification of FOXE3 from cDNA from a lymphoblastoid cell line of PID IV-1 (in quadruplicate). The internal control of GAPDH amplifying a 170 bp fragment to check for presence of cDNA (and absence of gDNA) is shown below. A genomic control is shown to the right, and the 278 bp fragment amplified from GAPDH exclusively in gDNA. (b, top) Electropherogram of the novel, non-stop mutation in FOXE3 (c.959 G>T: p.X320L) identified in all affected family members. (Bottom) Electropherogram of the region surrounding the stop codon of FOXE3 from the cDNA of an affected patient (PID IV-1) isolated from a lymphoblast cell line.