Expansion of the CCDC22 associated Ritscher-Schinzel/3C syndrome and review of the literature: Should the minimal diagnostic criteria be revised

The Ritscher-Schinzel syndrome (RTSCS) is a rare condition with craniofacial, cardiac and fossa posterior abnormalities. RTSCS is subdivided into Ritscher-Schinzel syndrome 1 (RTSCS1) caused by pathogenic variants in coiled-coil domain-containing protein 22 (CCDC22), and Ritscher-Schinzel syndrome 2 (RTSCS2) caused by pathogenic variants in WASH complex subunit 5 (WASHC5). CCDC22 is inherited in an X-linked recessive manner while WASHC5 is inherited in an autosomal recessive manner. Only 17 individuals with a molecular diagnosis are reported. In the past, the diagnosis of RTSCS was solely based on the clinical findings, and minimal diagnostic criteria has been proposed for the syndrome: Cardiac malformations (other than isolated patent ductus arteriosis), fossa posterior malformations, and certain dysmorphic features. However, those criteria are not present in all patients. We aim to further delineate the spectrum of CDCC22 associated RTSCS and present a novel patient with epileptic encephalopathy due to a presumed disease causing CCDC22 missense variant inherited from a healthy mother and grandmother. An affected maternal uncle had passed away at the age of 12 months and was thus unavailable for genetic testing. The proband and the maternal uncle had the typical facial dysmorphism associated with RTSCS, and they closely resembled previously published RTSCS2 patients with a molecular diagnosis. This suggests that RTSCS1 and RTSCS2 patients have a similar facial gestalt. We also review the literature on RTSCS, we explore potential differences and similarities between CCDC22 and W ASHC5 associated RTSCS and discuss the minimal diagnostic criteria.