The role of Frizzled-4 mutations in familial exudative vitreoretinopathy and Coats disease.

AIM: The aim of this study is to assess the role of Frizzled-4 (FZD4) in familial exudative vitreoretinopathy (FEVR) and Coats disease. METHODS: Tissue samples were collected for DNA extraction and automated DNA sequencing of the two coding exons of FZD4 in both directions. Cases carrying a FZD4 mutation and demonstrating extreme disease severity were selected for direct automated sequencing of all coding exons of LRP5, NDP and TSPAN12. Clinical data were obtained for the purpose of identifying genotype-phenotype correlations. RESULTS: 68 probands were diagnosed as having autosomal dominant or sporadic FEVR. Eleven FZD4 mutations (five missense, three deletions, one insertion, two nonsense) were identified. Six of these mutations are novel, and none were found in 346 control chromosomes. In 16 cases of Coats disease, one polymorphism combination was found in two samples: no mutations were detected. No genotype-phenotype correlation emerged. Three severely affected cases with FZD4 mutations failed to show additional mutations in the three other FEVR genes. CONCLUSION: The authors identified 12 FEVR probands with FZD4 mutations. FZD4 mutation screening can be a useful tool especially in mild or atypical cases of FEVR. Germ-line mutations in FZD4 do not appear to be a common cause of Coats disease.

Severe retinopathy of prematurity associated with FZD4 mutations.

PURPOSE: To determine whether mutations in the FZD4 gene are a risk factor for developing severe ROP. METHODS: Three Canadian tertiary care centers recruited premature infants prospectively and retrospectively, and assigned affectation status based on the maximum degree of severity of ROP recorded in both eyes. Mutation screening of the FZD4 gene was performed using direct sequencing. All sequence changes were evaluated for functional significance. RESULTS: Two novel FZD4 mutations (Ala370Gly or Lys203Asn) were identified in two infants from the severe ROP group (n=71). No mutation was detected in the mild to no ROP group (n=33), and the two novel mutations were absent in 173 random Caucasian samples. Mutation Ala370Gly was also found in one sibling and one parent of the affected infant, but no signs of familial exudative vitreoretinopathy (FEVR), a condition with phenotypic overlap with ROP known to be caused by FZD4 mutations, were present in either family member. CONCLUSIONS: Mutations in the FZD4 gene in this group of premature infants supports a role for the FZD4 pathway in the development of severe ROP and accounts for approximately 3% of severe ROP in Caucasian premature infants.

Mutant frizzled-4 disrupts retinal angiogenesis in familial exudative vitreoretinopathy.

Familial exudative vitreoretinopathy (FEVR) is a hereditary ocular disorder characterized by a failure of peripheral retinal vascularization. Loci associated with FEVR map to 11q13-q23 (EVR1; OMIM 133780, ref. 1), Xp11.4 (EVR2; OMIM 305390, ref. 2) and 11p13-12 (EVR3; OMIM 605750, ref. 3). Here we have confirmed linkage to the 11q13-23 locus for autosomal dominant FEVR in one large multigenerational family and refined the disease locus to a genomic region spanning 1.55 Mb. Mutations in FZD4, encoding the putative Wnt receptor frizzled-4, segregated completely with affected individuals in the family and were detected in affected individuals from an additional unrelated family, but not in normal controls. FZD genes encode Wnt receptors, which are implicated in development and carcinogenesis. Injection of wildtype and mutated FZD4 into Xenopus laevis embryos revealed that wildtype, but not mutant, frizzled-4 activated calcium/calmodulin-dependent protein kinase II (CAMKII) and protein kinase C (PKC), components of the Wnt/Ca(2+) signaling pathway. In one of the mutants, altered subcellular trafficking led to defective signaling. These findings support a function for frizzled-4 in retinal angiogenesis and establish the first association between a Wnt receptor and human disease.