BACKGROUND: Axenfeld-Rieger syndrome (ARS) is characterised by typical anterior segment anomalies, with or without systemic features. The discovery of causative genes identified ARS subtypes with distinct phenotypes, but our understanding is incomplete, complicated by the rarity of the condition. METHODS: Genetic and phenotypic characterisation of the largest reported ARS cohort through comprehensive genetic and clinical data analyses. RESULTS: 128 individuals with causative variants in PITX2 or FOXC1, including 81 new cases, were investigated. Ocular anomalies showed significant overlap but with broader variability and earlier onset of glaucoma for FOXC1-related ARS. Systemic anomalies were seen in all individuals with PITX2-related ARS and the majority of those with FOXC1-related ARS. PITX2-related ARS demonstrated typical umbilical anomalies and dental microdontia/hypodontia/oligodontia, along with a novel high rate of Meckel diverticulum. FOXC1-related ARS exhibited characteristic hearing loss and congenital heart defects as well as previously unrecognised phenotypes of dental enamel hypoplasia and/or crowding, a range of skeletal and joint anomalies, hypotonia/early delay and feeding disorders with structural oesophageal anomalies in some. Brain imaging revealed highly penetrant white matter hyperintensities, colpocephaly/ventriculomegaly and frequent arachnoid cysts. The expanded phenotype of FOXC1-related ARS identified here was found to fully overlap features of De Hauwere syndrome. The results were used to generate gene-specific management plans for the two types of ARS. CONCLUSION: Since clinical features of ARS vary significantly based on the affected gene, it is critical that families are provided with a gene-specific diagnosis, PITX2-related ARS or FOXC1-related ARS. De Hauwere syndrome is proposed to be a FOXC1opathy.

Byers Eye Institute Department of Ophthalmology Stanford University and Stanford Children's Health Stanford California USA

Center for Development Behavior and Genetics SUNY Upstate Medical University Syracuse New York USA

Department of Biology and Medical Genetics 2nd Faculty of Medicine Charles University and General University Hospital Prague Prague Czech Republic

Department of Cell Biology and Human Anatomy UC Davis School of Medicine Davis California USA

Department of Clinical Genetics Alberta Children's Hospital Calgary Alberta Canada

Department of Family Medicine McMaster University Hamilton Ontario Canada

Department of Medical Genetics Spectrum Health Grand Rapids Michigan USA

Department of Ophthalmology 1st Faculty of Medicine Charles University and General University Hospital Prague Prague Czech Republic

Department of Ophthalmology Medical College of Wisconsin Milwaukee Wisconsin USA

Department of Ophthalmology School of Medicine Ankara University Ankara Turkey

Department of Pediatric Radiology Medical College of Wisconsin and Children's Wisconsin Milwaukee Wisconsin USA

Department of Pediatrics and Children's Research Institute Medical College of Wisconsin and Children's Wisconsin Milwaukee Wisconsin USA

Department of Pediatrics and Inherited Metabolic Disorders 1st Faculty of Medicine Charles University and General University Hospital Prague Prague Czech Republic

Department of Pediatrics Geisinger Medical Center Danville Pennsylvania USA

Department of Pediatrics University of Iowa Iowa City Iowa USA

Department of Radiology 1st Faculty of Medicine Charles University and General University Hospital Prague Prague Czech Republic

GeneDx Gaithersburg Maryland USA

Gennet Centre for Fetal Medicine and Reproductive Genetics Prague Czech Republic

Pediatric Ophthalmology and Ocular Genetics Flaum Eye Institute Golisano Children's Hospital and University of Rochester Rochester New York USA

Unidad de Genética División de Pediatría Facultad de Medicina Pontificia Universidad Católica de Chile Santiago Chile

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