Summary

• A clinical syndrome with diverse genetic causes that results in profoundly impaired combined cellular and humoral immunity.
• Early diagnosis is imperative as, without treatment, the condition is uniformly fatal in the first year of life.
• Any child under the age of 1 year with an absolute lymphocyte count (ALC) of <3000/mm^3 should be investigated.
• Haematopoietic stem cell transplantation, gene therapy, or enzyme replacement therapy (when applicable) are the definitive treatments.
• Infants present with recurrent infections, failure to thrive, and chronic diarrhoea. Key findings on examination may include the absence of lymphoid tissue, poor weight gain, or diffuse erythematous rash.
• Live vaccines should not be given to infants with suspected SCID.
• Blood or blood products should be irradiated and test serologically negative for cytomegalovirus (CMV) infection before administration to patients with confirmed or suspected SCID.