Intragenic loss-of-function variants in transcription factors MAZ, FOXP1 and SIN3B in colobomatous microphthalmia

Despite the identification of many genes involved in developmental eye phenotypes, a large percentage of families lack genetic diagnoses, suggesting novel mechanisms remain to be discovered. Large deletions of 16p11.2, 3p14 or 19p13.11 regions involving transcription factors MAZ, FOXP1 and SIN3B, correspondingly, along with other genes, have been previously reported in individuals with neurodevelopmental and variable other features, including ocular coloboma and/or microphthalmia; recently, intragenic variants in FOXP1 and SIN3B have also been shown to cause neurodevelopmental phenotypes, with developmental eye defects reported in a small number of individuals with FOXP1 variants. Through exome sequencing analysis we identified novel splicing variants in MAZ and SIN3B, and a recurrent nonsense allele in FOXP1 in unrelated families affected with colobomatous microphthalmia, all with predicted loss-of-function effects; additionally, we report two new families with coloboma and 16p11.2 genomic deletions including MAZ, one de novo and another inherited from an affected parent. These findings provide further support for a role for FOXP1 in structural eye phenotypes, expanding its spectrum to include colobomatous microphthalmia, and suggest a role for MAZ and SIN3B in human eye development and disease.