Adenosine Deaminase Severe Combined Immunodeficiency (ADA-SCID): Causes, Symptoms, Diagnosis, Treatments

Medically Reviewed by Dr. K. on 13 May 2022.

What Is Adenosine Deaminase Severe Combined Immunodeficiency (ADA-SCID)?

Your immune system can't fend off even minor infections when you have severe combined immunodeficiency (SCID). Your body's defenses stop functioning because of a problem with your genes in adenosine deaminase severe combined immunodeficiency (ADA-SCID).

ADA-SCID is a debilitating illness that typically manifests in childhood. Treatments will improve, and patients who undergo care before an illness develops have a higher chance of living a healthy and stable life.

The ADA gene is present in everybody. If you have ADA deficiency, you have a mutation of yours. As a result, the body produces insufficient amounts of an enzyme that helps the white blood cells shield you from infection. You will quickly get infected if you don't have enough protection.

If your child is born with ADA deficiency, he will almost certainly be diagnosed with SCID before the age of six months. If the condition develops later in life, the symptoms may be milder.

You can control the symptoms and prevent infections with medication. When left unchecked, the body's ability to fight infections deteriorates, which can be fatal.

Causes

Adenosine deaminase deficiency is caused by mutations in the ADA gene. This gene gives instructions for producing the enzyme adenosine deaminase. Adenosine deaminase is found throughout the body, however, it is most active in specialized white blood cells called lymphocytes. Our white blood cells protect us by making immune proteins called antibodies or by directly attacking infected cells. Lymphocytes are produced in specialized lymphoid tissues including the thymus, which is a gland located behind the breastbone, and lymph nodes, which are found throughout the body. Both our lymphocytes in the blood and in lymphoid tissues make up the immune system.

The function of the adenosine deaminase enzyme is to eliminate molecules called deoxyadenosine, which is generated when DNA is broken down. Adenosine deaminase converts deoxyadenosine, which can be toxic to lymphocytes, to another non-harmful molecule called deoxyinosine. Mutations in the ADA gene reduce or eliminate the activity of adenosine deaminase and allow the buildup of deoxyadenosine to levels that are toxic to lymphocytes.

Immature lymphocytes in the thymus are particularly vulnerable to a toxic buildup of deoxyadenosine. These cells die before they can mature to help fight infection. The number of lymphocytes in other lymphoid tissues is also greatly reduced. The loss of infection-fighting cells results in the signs and symptoms of SCID.

If any of your parents pass down a copy of a mutated gene to you will you develop ADA-SCID. You won't get the disorder if you get a copy from only one parent, but you can pass it on to your own children.

 

Symptoms

Symptoms are most common in the first few months of life. If your child has this disorder, they can develop a number of infections in their body, including:

  • Ear
  • Sinus
  • Mouth
  • Lung
  • Skin

Infections in babies are very common. Pay particular care if your child suffers from them frequently and they:

  • Are serious
  • Lasts long
  • Are unusual
  • Frequently recur

Diarrhea and extensive skin rashes are common in children with ADA-SCID. They can also be slow to develop and progress slowly in other areas of growth, such as motor and social skills.

The signs may be mild at first if the condition does not manifest until later in adolescence or adulthood. The first symptoms may include recurring ear or upper-respiratory infections.

Getting a Diagnosis

Early diagnosis and recovery improve the odds of leading a healthy life.

Most countries mandate all newborns to be screened for ADA-SCID. At any age, you can be examined. A doctor will draw blood and test it to see if the immune system is functioning properly.

To detect ADA-SCID, a doctor may need to do more than one blood test.

Your doctor may like to know the following:

  • What infections have you (or your child) experienced?
  • What was the duration of their infection?
  • Are they gone now that you've had treatment?
  • Have they returned?
  • Is there anybody else in your family who suffers from immune system issues?
  • Has someone in your family got their DNA tested?

If you or your child is diagnosed with ADA-SCID, your doctor can prescribe genetic counseling and early blood tests for both of your children.

Questions for Your Doctor:

  • Do I need to undergo some more tests?
  • What is the seriousness of my condition?
  • Have you ever worked for someone who had this problem?
  • What medications will I be required to take?
  • What resources can I use to learn more?
  • What resources can I use to find other families who are struggling with ADA-SCID?
  • How will I prevent being infected?
  • Is it possible for me to participate in clinical trials? How do you do it?
  • Will the rest of the family get it?

Treatment

You should begin therapy right away. Look for a doctor who specializes in immune deficiencies.

To cure any latent illnesses, the doctor will administer antibiotics, antifungals, or antiviral drugs.

Antibiotics may be used by the doctor to avoid new infections. A baby or child with ADA-SCID may need to remain in an isolated hospital room for a period of time, but their parents will be allowed to stay with them.

Enzyme replacement therapy (ERT) can help your immune system function better and avoid infections, even if it does not cure the disease. In this treatment, you are given doses of safe enzymes, which are normally obtained from a cow.

A stem cell transplant is the best way to treat ADA-SCID. Doctors will aim to regenerate your immune system by injecting stable stem cells into your body. It functions well in babies and where the donor stem cells are from a similar family member. Chemotherapy may be needed before a transplant in some cases to destroy damaged cells.

More treatments for ADA-SCID are being researched by scientists. Good genes are added to your own cells in the lab and then transplanted back into the body to correct defective cells in these trials.

Taking Care of Yourself or Your Child

If you or your kid has ADA-SCID, try to stay away from diseases as far as possible. Wash your hands often, avoid contact with sick people, and consult your doctor before receiving any vaccines. Vaccines made of live viruses should be prevented at all times. Rotavirus, MMR, chickenpox, and the flu vaccine in mist form are among them. (Other flu vaccines are available that do not contain the live virus.)

Make sure you look after yourself. To keep your body safe, eat well, exercise enough, and get enough sleep.

Stay in touch with the doctor and arrange daily checkups.

Seek help and support. Other families affected by the illness may be able to assist. Chat about your issues and get advice about how to make your life better.

 

What to Expect

The timing of your treatment is important. Babies with ADA-SCID rarely survive through their second birthdays without it. Many that receive care before illnesses occur, on the other hand, will live long and stable lives.

 

Getting Support

Visit the Immune Deficiency Foundation's website to read more about ADA-SCID. There are references on the website to help you communicate with other families that are dealing with the same problem.

Sources

Referenced on 2.3.2021:

  1. American Society of Gene & Cell Therapy: ''Gene Therapy for Genetic Disorders.''
  2. Baby’s First Test: ''Severe combined immunodeficiency.''
  3. GeneReviews: ''Adenosine Deaminase Deficiency.''
  4. Great Ormond Street Hospital for Children NHS Trust: “Severe combined immunodeficiency (SCID) information."
  5. Nemours Foundation: ''Severe Combined Immunodeficiency.''
  6. Pai, S. New England Journal Of Medicine, published online July 31, 2014.
  7. NIH: ''Adenosine deaminase deficiency.''
  8. Immune Deficiency Foundation: ''About Primary Immunodeficiency'' and ''Severe Combined Immune Deficiency and Combined Immune Deficiency.''
  9. https://www.webmd.com/a-to-z-guides/adenosine-deaminase-severe-combined-immunodeficiency#1

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