What is SCID?
Severe combined immunodeficiency (SCID)
SCID is a primary immunodeficiency disease. It is a rare fatal syndrome of diverse genetic disorders. The prevalence is around 1 in 100,000 births. Its life expectancy is less than a year without treatment. Infants die from an array of infections associated with a lack of lymphocytes in the blood, which are required to fight off infections.
There are currently fourteen known different types of SCID that cause the absence of T-lymphocyte, B-lymphocyte function and natural killer cells function. These defects lead to extreme susceptibility to serious infections.
Normal kid
Different genetic causes of SCID
The most common are SCID X-lined and Adenosine Deaminase Deficiency (ADA). All types of SCID are due to genetic defects. These defects can be inherited from the parents or can be due to new mutations that arise in the affected infant.
The most common symptoms is an excessive number of infections. These infections can be more serious than the infections that normal children have. A baby with SCID will have recurrent bacterial, viral, or fungal infections that are much more serious and less responsive to treatment than would normally be expected. These can include ear infections (acute otitis media), sinus infections (sinusitis), oral thrush (a type of yeast infection in the mouth), skin infections, meningitis, and pneumonia. Infants with SCID also have chronic diarrhoea.
The diagnosis is usually first suspected in children because of the above clinical features. However, in some instances there has been a previous child with SCID in the family and this positive family history may prompt the diagnosis even before the child develops any symptoms. One of the easiest ways to diagnose this condition is to count the peripheral blood lymphocytes in the child (or those in the cord blood). This is done by two tests: the complete blood count and the manual differential, which is a count of the percentage of each different type of white cell in the blood.
