Signs, symptoms and diagnosis of ADA-SCID

There may also be problems with other body systems, including the kidneys, liver and lungs.

How is it diagnosed?

Infants with typical early onset ADA-SCID have poor growth and frequent, severe and unusual infections, such as pneumonia with an organism called Pneumocystis jirovecii (a yeast-like fungus) that does not usually cause illness in healthy individuals. Breathing difficulties can also occur in infants with ADA-SCID without any detectable infection.

Blood count testing shows a very low lymphocyte count, and basic immunology tests show very low or absent levels of T, B and NK lymphocytes. Doctors refer to this pattern of SCID as ‘T -, B -, NK - SCID’, and this is highly suggestive of a diagnosis of ADA-SCID. The level of ADA enzyme activity in the blood can be measured and is usually less than one per cent of the normal levels seen in healthy children. Additionally, the levels of adenosine can be measured and will be much higher than normal.

Other (non-immunology) investigations

If ADA deficiency is confirmed, it is important to assess hearing as early as possible because of the high risk of deafness. A psychologist will also carry out a developmental assessment. The need for other investigations will depend on whether other systems of the body are involved.

Reviewed February 2018