RESUMEN
Immunoglobulin class switch recombination deficiencies [Ig CSR deficiencies] or Hyper IgM syndromes [HIGM] are a group of primary immunodeficiency diseases, characterized by defective CD40 signaling of B cells resulting into a CSR and a somatic hypermutation. The affected patients are characterized with reduced serum levels of IgG and IgA, and normal or elevated level of IgM, which lead to increased susceptibility to infections. We describe a 3 year-old boy with frequent bacterial infections of the skin and respiratory tract, mucosal ulcers, and diarrhea. He experienced onychomadesis in both fingernails and toenails during recent bacterial infection. Quantitative immunoglobulin levels revealed high levels of serum IgM and very low levels of IgG, IgA, and IgE. Clinical and immunologic studies supported the diagnosis of HIGM. Onychomadesis as a finding in HIGM could be considered. Considering exclusion of CD40L, CD40, AID and UNG genes by molecular analysis, new CSR selective deficiencies could be suspected in this case