Diagnosis of <i>TET3</i>‐Related Beck–Fahrner Syndrome in an Individual With Chorioretinal and Iris Colobomata Using a <scp>DNA</scp> Methylation Signature

Disorders of developmental delay can occur from pathogenic variants in genes responsible for epigenetic regulation. Heterozygous and biallelic pathogenic variants in TET3 have recently been described in TET3-related Beck-Fahrner syndrome (TET3-BEFAHRS), representing an autosomal dominant disorder with variable expressivity. Typical features include intellectual disability and developmental delay. Patients can also present with facial dysmorphism, seizure disorder, ophthalmic findings, and other neurobehavioral features. As the condition has recently been described and few patients have been reported in literature, the full scope of the phenotypic spectrum and approaches to identify them are still emerging. We report an individual meeting the criteria for TET3-BEFAHRS confirmed through clinical, genetic, and DNA methylation episignature analysis, who uniquely presents with bilateral chorioretinal and unilateral right iris colobomata. This case suggests a broader ophthalmic phenotype to TET3-BEFAHRS and demonstrates the utility of episignatures for the diagnosis of Mendelian disorders of epigenetic machinery.