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Nanophthalmos and posterior microphthalmos are ocular abnormalities in which both eyes are abnormally small, and typically associated with extreme hyperopia. We recruited 40 individuals from 13 kindreds with nanophthalmos or posterior microphthalmos, with 12 probands subjected to exome sequencing. Nine probands (69.2%) were assigned a genetic diagnosis, with variants in MYRF, TMEM98, MFRP, and PRSS56. Two of four PRSS56 families harboured the previously described c.1066dupC variant implicated in over half of all reported PRSS56 kindreds, with different surrounding haplotypes in each family suggesting a mutational hotspot. Individuals with a genetic diagnosis had shorter mean axial lengths and higher hyperopia than those without, with recessive forms associated with the most extreme phenotypes. These findings detail the genetic architecture of nanophthalmos and posterior microphthalmos in a cohort of predominantly European ancestry, their relative clinical phenotypes, and highlight the shared genetic architecture of rare and common disorders of refractive error.

PurposeRefractive error is caused by a disparity between the axial length and focusing power of the eye. Nanophthalmos is a rare ocular abnormality in which both eyes are abnormally small, typically causing extreme hyperopic refractive error, and associated with an increased risk of angle-closure glaucoma.MethodsA cohort of 40 individuals from 13 unrelated nanophthalmos kindreds were recruited, with 11 probands subjected to exome sequencing.ResultsNine probands (69.2%) were assigned a genetic diagnosis, with variants in PRSS56 (4), MFRP (3), and previously reported variants in TMEM98 (1) and MYRF (1). Two of the four PRSS56 probands harboured the previously described c.1066dupC frameshift variant implicated in over half of all reported PRSS56 kindreds, with surrounding haplotypes distinct from each other, and from a previously reported Tunisian c.1066dupC haplotype. Individuals with a genetic diagnosis had shorter mean axial lengths (P=7.22×10−9) and more extreme hyperopia (P=0.0005) than those without a genetic diagnosis, with recessive forms associated with the shortest axial lengths and highest hyperopia. All individuals with an axial length below 18 mm in their smaller eye (17/17) were assigned a genetic diagnosis.ConclusionsThese findings detail the genetic architecture of nanophthalmos in an Australian cohort of predominantly European ancestry, their relative clinical phenotypes, and highlight the shared genetic architecture of rare and common disorders of refractive error.