Nesrine Radwan, assistant lecturer of pediatrics, faculty of medicine, Ain Shams University, Cairo, Egypt.

Severe combined immunodeficiency (SCID) is a life-threatening syndrome of recurrent infections, diarrhea, dermatitis, and failure to thrive. It is caused by numerous molecular defects that lead to severe compromise in the number and function of T cells, B cells, and occasionally natural killer (NK) cells. Clinically, most patients present before age of 3 months and death occurs around 2 years due to infection. SCID is considered a pediatric emergency because survival depends on expeditious stem cell reconstitution, usually by bone marrow transplantation (BMT).

All forms of SCID are inherited either as AR or XL. X-linked SCID results from a mutation in the interleukin 2 receptor gamma (IL2RG) gene which produces the common gamma chain subunit, a component of several IL receptors. JAK3 mutation, located on chromosome 19, can also result in SCID. Another type of SCID is caused by mutations in a gene that encodes an enzyme called adenosine deaminase (ADA) (2nd most common) (T-, B- and NK-) which is essential for the metabolic function of a variety of body cells especially T-cells, or deficiency of the Alpha Chain of the IL-7 Receptor (T-,B+,NK+)(3rd most common). Other types of SCID (CD3 Chains, Deficiency of CD45 ; recombinase activating genes 1 and 2 ( RAG1 and RAG2 deficiency)) encode proteins necessary for the development of the immune recognition receptors on T- and B-lymphocytes (in some instances mutations in these genes also cause Omenn’s Syndrome). As for Artemis, Cernunnos and Ligase 4 deficiency, infants with these types of SCID lack T- and B-lymphocytes but have NK-lymphocytes (T-B-NK+ phenotype). Thera are also less Severe Combined Immunodeficiencies, such as MHC class-II deficiency, purine nucleoside phosphorylase (PNP) deficiency, ZAP70 deficiency, CD25 deficiency, Cartilage-Hair Hypoplasia, Coronin 1A deficiency and MHC class I deficiency. Sometimes a child with clinical CID is found to have a mutation in a gene that would be expected to result in SCID, but does not have the typically severe disease as anticipated. This situation is often called “leaky” SCID.

Severe infection is the most common presenting symptom of patients with SCID. Children with SCID may develop infections caused by organisms or vaccines, which are usually not harmful in children who have normal immunity. Among the most dangerous is an organism called Pneumocystis jiroveci, which can cause a rapidly fatal pneumonia (PCP) if not diagnosed and treated promptly. Another dangerous organism is the chicken pox virus (varicella).  Other features include chronic diarrhea, persistent oral monaliasis and failure to thrive. One of the easiest way to diagnose is the presence of lymphopenia, with decreased T-cell subtype. Immunoglobulin levels are usually very low in SCID. Curative treatment is achieved by stem cell transplantation from matching donor. The supportive management is by intravenous immunoglobulin and cotrimoxazole.

Case Presentation: We present a six month old male patient, firstborn from first-degree cousins. At the age of four months, he started to suffer from persistent fever, diarrhea and napkin dermatitis. His CBC showed leucopenia with marked lymphopenia (TLC: 3.5X109/L, Lymphocytes: 1.2x109/L). Serum immunoglobulin (Ig) levels were as follows: Ig A:35 mg/dl, Ig, IgM:42 mg/dl, IgG:240 mg/dl and E: 25 IU/L. Analysis of lymphocyte subsets by flow cytometry revealed the followings: CD3: 5.6%, CD4: 26.9%, CD8: 54.6%, CD19: <1%, CD45RA: 31.1%, CD45RO: 92.2%. Few days later he developed severe pallor and tachycardia, and the hemoglobin level dropped to 3 mg/dl. He received irradiated washed packed red cells.  The diagnosis of fetomaternal engraftment was put forward because of low CD45RA and high CD45RO, and consequently oral steroid therapy was initiated at a dose of 0.5 mg/kg/day.

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