Right after they're born, babies are protected from
infections by immunity transmitted to them by their mothers. Within
the next few months, though, their immune systems develop and begin
to assume responsibility for fighting off infections. But
sometimes, babies have immune deficiencies and they don't have
the ability to fight off routine infections on their own.
The symptoms of immune deficiency depend on what part of the
immune system is affected and can range from mild to
life-threatening. One example of a life-threatening immune
deficiency is severe combined immunodeficiency (SCID).
SCID, which is believed to be rare, can be successfully treated
if it's identified early. Otherwise, it can be fatal within the
first year of life.
What Is SCID?
SCID is actually a group of inherited disorders that cause
severe abnormalities of the
. These disorders lead to reduced or malfunctioning T- and
B-lymphocytes, the specialized white blood cells made in the bone
marrow to fight infection. When the immune system doesn't
function properly, it can be difficult or impossible for it to
battle viruses, bacteria, and fungi that cause infections.
Called "combined" immune deficiency because it affects
the function of two kinds of infection-fighting cells where other
immune system diseases involve only one, there are several forms of
SCID. The most common type is caused by a problem in a gene found
on the X chromosome and affects only males. Females may be carriers
of the condition, but because they also inherit a normal X
chromosome, the abnormal X may be canceled out. Males, on the other
hand, only have one X chromosome.
Another form is caused by a deficiency of the enzyme adenosine
deaminase (ADA). Other cases of SCID are caused by a variety of
other genetic defects.
Classic signs of SCID include an increased susceptibility to
failure to thrive
as a result of infections. A baby with SCID may 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 may also have chronic diarrhea. If a child has these
symptoms, a doctor will test for SCID or other types of immune
Parents who have a child with SCID or a family history of
immunodeficiency might want to consider genetic counseling and
early blood testing, since early diagnosis can lead to prompt
treatment and improve the chances of a good outcome. It may also be
possible to test a high-risk baby for the disease before birth if
the genetic mutation causing SCID in a family is known. Babies born
with SCID can have a healthy immune system if they are treated
early in life.
Most children without a known family history of the disease are
not diagnosed until 6 months of age or older.
When a child is diagnosed with SCID, a referral typically is
made to a doctor who specializes in treating immune deficiencies -
usually a pediatric immunologist or pediatric infectious disease
It's important to prevent infections in kids with SCID, so
your doctor may prescribe antibiotics to prevent infection and
advise keeping the child away from crowds and sick people.
Children with SCID should not be immunized with live viruses -
like the chickenpox (varicella) or measles, mumps, and rubella
(MMR) vaccines - because they lack the normal defense of antibodies
to the viruses. Introducing a virus, even a weakened vaccine virus,
can be dangerous.
Doctors may also administer an infusion of intravenous immune
globulin (IVIG) to help the body fight infection.
The most effective treatment for SCID is a
stem cell transplant
. This is when stem cells - cells found primarily in the bone
marrow from which all types of blood cells develop - are introduced
into the body in the hopes that the new cells will rebuild the
To provide the best chances for success, a transplant is usually
done using the bone marrow of a sibling. However, a parent's
marrow might also be acceptable. Some children do not have family
members who are suitable donors - in such cases, doctors may use
stem cells from an unrelated donor. The likelihood of a good
outcome also is higher if the transplant is done early, within the
first few months of life, if possible.
Some SCID patients require chemotherapy before their transplant.
Chemotherapy will destroy cells in the bone marrow to make room for
the donated cells and help prevent the child's immune cells
from attacking the donated cells. Other kids with SCID may not need
such treatment, especially if they have very few immune cells to
start with. The use of pre-transplant chemotherapy depends on the
severity of the immune deficiency, the type of SCID, the donor
used, and the transplant center.
In cases of SCID caused by a missing enzyme, the enzyme can be
replaced via a weekly injection. This is not a cure and these
children must receive the injections for the rest of their
Another treatment approach currently being studied is
. This involves removing cells from a child with SCID and inserting
healthy genes into them, then transplanting them back into the
child. When they find their way to the bone marrow, they can start
to produce healthy immune cells. Gene therapy has been successful
for some patients with certain types of SCID, but a few children
treated with it developed complications, so it has not yet become
routine treatment. New trials of gene therapy are ongoing.
Caring for Your Child
Babies who have had bone marrow transplants may need additional
treatment with antibiotics or immunoglobulins. Your doctor will
advise you about these.
Until your child's immune system develops adequate
protection after a bone marrow transplant, you can help reduce the
risk of infection by having your child wear a mask. A mask can also
serve as a signal to others that your child is trying to avoid
Understand that infants with SCID may have to endure many
painful procedures and repeated hospital stays. And that can be
stressful and difficult for the entire family. Luckily, this
doesn't have to be handled alone: support groups, social
workers, and family friends often can lend a helping hand. It's
important to reach out for support during this time.
When to Call the Doctor
If you're concerned that your child has more frequent
infections than usual, discuss the possibility of immune deficiency
with your doctor. If your child has a serious infection, contact
your doctor immediately. Because early treatment is more
successful, you can improve your child's chances of developing
a healthy immune system by acting quickly. If your child has SCID,
any illness merits close medical attention.
Elana Pearl Ben-Joseph, MD
Date reviewed: October 2006
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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