Immunology - Severe Combined Immunodeficiency

Question 1

What causes Severe combined immunodeficiency?

Answer 1

50% of cases caused by common gamma chain mutations on the X chromosome that codes for IL receptors on T and B cells

Absent or dysfunctional T and B cells

X-linked recessive

Most severe condition causing immunodeficiency

Question 2

What other genetic mutations can cause SCID?

Answer 2

JAC3 gene mutations
Adenosine deaminase deficiency

Question 3

When does SCID first present?

Answer 3

First few months of life

Question 4

How does SCID present?

Answer 4

• Persistent severe diarrhoea
• Failure to thrive
• Opportunistic infections, more frequent or severe than in normal kids e.g. severe and fatal chickenpox, PCP and CMV
• Unwell after live vaccines e.g. BCG, MMR, nasal flu vaccine
• Omenn syndrome

Question 5

What causes Omenn syndrome?

Answer 5

Rare cause of SCID

Result of a mutation in the recombination-activating gene (RAG 1 or RAG 2)

Codes for important proteins in T and B cells

Autosomal recessive

Question 6

What is Omenn syndrome?

Answer 6

Abnormally functioning and deregulated T cells that attack tissues in the foetus or neonate

Question 7

What are the classic features of Omenn syndrome?

Answer 7

• Red, scaly, dry rash (erythroderma)
• Alopecia
• Diarrhoea
• Failure to thrive
• Lymphadenopathy
• Hepatosplenomegaly

Question 8

How is SCID managed?

Answer 8

Fatal unless successfully treated

Specialist immunology centre

• Treat underlying infections
• Immunoglobulin therapy
• Minimising new infection risk (sterile environment)
• Avoiding live vaccines
• Heamopoietic steml cell transplantation