AICDA and hyper-IgM syndrome type 2: Since the first report of bi-allelic AICDA variants in 12 unrelated families as causal for an autosomal recessive form of HIGM syndrome (HIGM-2; AR-AID) [23], various missense and nonsense variants in exons 2, 3, or 4 of AICDA have been reported [23–26].