Neonatal-Onset Familial Mediterranean Fever in an Infant with Human Parainfluenza Virus-4 Infection.

Unusual, severe infections or inflammatory episodes in newborns and infants are largely unexplained and often attributed to immature immune responses. Inborn errors of immunity (IEI) are increasingly recognized as the etiology of life-threatening inflammatory and infectious diseases in infancy. We describe a patient with a unique neonatal-onset Familial Mediterranean Fever (FMF) due to compound heterozygous variants in MEFV, presenting as pleuritis following human parainfluenza virus-4 infection. Diagnostic challenges of FMF in infancy include the interpretation of the attacks as infectious episodes. Newborns and infants with acute, recurrent, or chronic, unusually severe infectious or inflammatory conditions should be screened for IEI, including both disorders with defective immunological responses and autoinflammatory disorders.