14th February 2024

Examples

DiGeorge syndrome

Also known as 22q11.2 deletion syndrome, it is named due to a deletion on a small part of chromosome 22. It is an autosomal dominant condition whose clinical symptoms are due to a defect in the development of pharyngeal arches in the embryonic stage. Clinical manifestations can vary, but the classic triad is a hypoplastic thymus, hypocalcaemia and cardiac anomalies. The immunodeficiency comes from the hypoplastic thymus, the site of T cell maturation. Patients are noted to have recurrent sinus and respiratory infections. There is no specific treatment, but prompt administration of antibiotics is advised when indicated. Diagnosis is with genetic studies, usually via fluorescence in situ hybridisation (FISH).

Ataxia telangiectasia

A rare autosomal recessive condition leading to early onset ataxic gait and cutaneous telangiectasia due to mutations in the ataxia telangiectasia mutated (ATM) gene. ATM is involved in immunoglobulin production and T cell proliferation, so two-thirds will also experience immune system involvement, typically with low IgG and IgA levels and low CD4 counts. They are predisposed to recurrent sinopulmonary infections. Typically, neurological features are noticed first, followed by telangiectasia, usually seen in the eye. The diagnosis is clinical but confirmed by demonstrating high alfa-fetoprotein levels; a brain MRI demonstrates cerebellar atrophy and low immunoglobulin levels. The treatment is supportive and often involves a multi-disciplinary team.

Severe common immune deficiency (SCID)

The most severe of the primary immunodeficiencies affecting both B and T cell formation. It was known as the “bubble boy disease” after the child with SCID who was raised in a sterile environment. Mortality rates are high without treatment, and patients are vulnerable to recurrent infections from opportunistic pathogens such as Pneumocystis Jirovecii and Cryptosporidium. Antibiotic and antiviral prophylaxis is usually indicated. The definitive treatment is stem cell transplantation.