Severe Combined Immunodeficiency (SCID) is a rare congenital disorder characterized by severely compromised host immune response.
This disease is typically seen in infants who carry genetic mutations from one of their parents, most commonly from the mother. abies are born without competent T-cell, B-cell and sometimes-natural killer (NK) cell mechanism.
SCID is also known as “the bubble boy disease” after David Vetter, who survived for nearly 13 years in an isolated germ-free box (referred as “bubble”).
Defects in the natural pathways that produce and propagate lymphocytes can result from at least thirteen different types of genetic defects. Compromised lymphocytes leave the natural defense systems of the body in a paralyzed state.
The body becomes overly sensitive to the infections caused by viruses, bacteria or fungi. The resulting diseases are usually lethal in SCID patients. An early diagnosis followed by an effective treatment can save the patient’s life.
Common Signs
Even though the genetic defects causing SCID could be of a wide variety. However, the clinical manifestations of the disease remain common. Typical sign of the disease is an increased vulnerability to serious infections such as skin infections, oral thrush, pneumonia, meningitis, acute ear infection, and sinusitis.
Children with SCID also often suffer from chronic diarrhea. In SCID patients, these infections become less responsive to treatments. In such patients, prescribed clinical tests should be performed to confirm the disease.
Conventional Identification
Pathologists specifically look for the B- and T-lymphocyte counts in the blood samples of the patients suspected for SCID. In addition to decreased lymphocyte counts, the samples also reveal low levels or absence of germ-fighting antibodies.
An early diagnosis of SCID can be of life-saving importance, which however is very rare because it is not a routine practice to carry out differential blood count tests in newborns.
SCID usually does not manifest clinically very soon after the baby is born. This is because the newborns with SCID thrive on the acquired immunity from the mother’s antibodies, at least for initial few weeks. However, the infants over the period of time get affected even by the weakened microbes in the vaccines such as polio, rotavirus, chicken pox, BCG etc. due to deprived immune defense.
On an average, the diagnosis of SCID happens when the infants cross the age of four to six months, only after the symptoms become apparent.
Early Diagnosis
The earliest intervention could be made by performing DNA sequencing from the fetus for any relevant gene mutations, when there is a potential risk because of a family history of immunodeficiency. Prenatal identification of SCID can give an ample amount of time for treating the baby after birth.
The second best approach is new-born screening. Collection of blood sample at the time of birth for counting T-cells and B-cells and an assessment of their functions can be done. Postnatal DNA testing can also be performed for a detailed diagnosis.
However, due to the time taken in preparation and testing of samples with current methods and the expensiveness of genetic tests, it may not be feasible to include them as a part of routine tests for the newborns. Also due to low overall prevalence of SCID, it may not be reasonable to carry out gene sequencing for each newborn.
Nevertheless, till the time large-scale genetic testing methods become affordable and time-efficient, at least differential white blood cell counting should be done as a part of routine postnatal tests, in order to rule out any possibility of SCID. This simple preventive measure before the onset of clinical manifestations can reduce the cost of the treatment and minimizes the suffering in patients diagnosed with SCID.
Further Reading