What is Severe Combined Immunodeficiency (SCID)?
Severe Combined Immunodeficiency (SCID) is the result of several defective genes in a child's immune system. Kids with SCID are extremely susceptible to life-threatening infections. SCID is sometimes known as the "bubble boy disease" because of the 1976 television movie about David Vetter, the boy who spent his childhood in a plastic bubble. Despite the extreme precautions to keep him safe from pathogens, David died after an unsuccessful bone marrow transplant when he was 12.
Severe combined immunodeficiency is quite rare. Researchers estimate only between 40-100 babies are born with SCID in the United States annually. The numbers may be higher, though, because there likely are infants who die from infections before they were diagnosed with SCID.
What are the different types of Severe Combined Immunodeficiency (SCID)?
There are two main types of SCID.
X-linked severe combined immunodeficiency (XSCID)
X-linked severe combined immunodeficiency (XSCID) results from mutations in a gene on the X chromosome. It only affects boys because males don't have a backup X chromosome to compensate for the flawed one. Because of this, SCID affects many more boys than girls
ADA deficiency SCID (ADA SCID)
ADA deficiency SCID (ADA SCID) involves a mutation on a protein that cells need to make new DNA. Without treatment, patients with ADA SCID will not survive.
What are the signs and symptoms of Severe Combined Immunodeficiency (SCID)?
Symptoms of SCID are both recurrent and severe.
If your baby shows any of the following symptoms in his first year of life, see a doctor:
- 8 or more ear infections
- Persistent oral thrush
- 2 or more cases of pneumonia
- Failure to thrive (or loses weight)
- Deep infections that affect an entire lung or the liver
- Infections that do not go away with antibiotics for two months or more
- Infections requiring intravenous (IV) antibiotic treatments
- A family history of immunodeficiencies (or if you've had other children die from infections)
How is Severe Combined Immunodeficiency (SCID) diagnosed?
Because SCID is both rare and inherited, it is hard to detect in children. There are fewer than 100 known cases of SCID each year in the United States, but some babies likely die from infections without ever being diagnosed with the condition. To make diagnosis even more difficult, most babies born with SCID are asymptomatic at birth due to protection from their mother’s antibodies. If your infant suffers from frequent viral, fungal or bacterial infections in the first year of life, see a doctor.
Tests and diagnoses
According to the American Association for Clinical Chemistry (AACC), identifying SCID in newborns is a pediatric emergency. SCID runs in families, so it is important to let your doctor know if you've had a child die from a severe infection in the past. New life-saving treatments make newborn screening for SCID more important than ever. Screening for SCID includes DNA sequencing - if there is a family history of immunodeficiency disease, doctors can perform this test to see if your child has it. Blood tests also will be performed to count T and B cells and determine their level of functioning, which also can indicate SCID in infants.
Diagnosing SCID before your child gets an infection could save his life. Without treatment, there is a 100 percent morbidity rate for children with the disease.
What are the causes of Severe Combined Immunodeficiency (SCID)?
Due to the genetic mutation, children with the type known as XSCID don’t produce enough disease-fighting B and T white blood cells; this is linked to the X chromosome. Kids with another form, called ADA SCID, don’t produce the enzyme adenosine deaminase, which compromises their immune system.
How is Severe Combined Immunodeficiency (SCID) treated?
While prenatal screening is becoming more common for a child with Severe Combined Immunodeficiency, it is still rarely diagnosed in newborns. Most infants with SCID aren't diagnosed until they are just over 6 months of age. Diagnosis usually follows several infections, or a child's failure to thrive.
- Isolating infants with a confirmed diagnosis of SCID is important to protect them from life-threatening germs
- Avoiding breastfeeding until the mother has been cleared of any exposure to certain infectious diseases is crucial
- Avoiding the injection of live attenuated vaccines
Hematopoietic cell transplantation (HCT)
- Stem cells transplanted from the bone marrow of a healthy donor can cure an infant with SCID. It is the best option for patients with the disease. The best donors are a baby's healthy siblings, which, unfortunately, is a rare situation. Other donors may include parents or close relatives or even strangers who are a good genetic match. The earlier a transplant is done, the better chance your child has to survive SCID.
- Enzyme replacement therapy can help children with ADA SCID until other treatment options are available
- Gene therapy is an emerging treatment for infants with SCID but, currently, it only works for certain forms of the disease and may have fatal side effects.