SIgMID has been characterized as arare primary immunodeficiency differentiated by a low serum IgM level, lessthan 2 SD or <10% of age adjusted normal controls or absolute levels of 10–20 mg/dL in infants and children [3].The earliest recognized cases were described in children in 1966 [9, 19]. Here, CD40LG is linked to inborn error of immunity.