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Severe combined immunodeficiency

Severe Combined Immunodeficiency, or SCID, is a genetic disorder in which both "arms" (B cells and T cells) of the adaptive immune system are crippled, due to a defect in one of several possible genes. SCID is a severe form of heritable immunodeficiency. It is also known as the "bubble boy" disease because its victims are extremely vulnerable to infectious diseases and must live (if untreated) in a completely sterile environment. The most famous case is the boy David Vetter. more...

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SCID affects about 1 in 80,000 live births. These babies, if untreated, usually die within 1 year due to severe, recurrent infections. Chronic diarrhea, ear infections, recurrent Pneumocystis jiroveci pneumonia, and profuse oral candidiasis commonly occur. Treatment options are much improved since David Vetter, and living in a bubble is no longer necessary.

Types

IL-7 signalling pathway

Most cases of SCID are derived from mutations in the γc chain in the receptors for interleukins IL-2, IL-4, IL-7, IL-9 and IL-15. These interleukins and their receptors are involved in the development and differentiation of T and B cells. Deleterious mutations in the gamma-chain or in the JAK3 protein cause a form of SCID that is characterized by low numbers of T and NK cells, and presence of non-functional B cells.

The IL-2 receptor γ (IL-2Rγ) gene is located on the X chromosome and mutation of this gene causes X-linked SCID.

Janus kinase-3 (JAK3) is an enzyme that mediates transduction downstream of the γc signal. Mutation of its gene also causes SCID.

VDJ recombination

The manufacture of immunoglobulins requires recombinase enzymes derived from the recombination activating genes RAG-1 and RAG-2. These enzymes are involved in the first stage of VDJ recombination, the process by which segements of a B cell or T cell's DNA are rearranged to create a new T cell receptor or B cell receptor (and, in the B cell's case, the template for antibodies). Certain mutations of the RAG-1 or RAG-2 genes prevent VDJ recombination, causing SCID.

Adenosine deaminase

Another well-known form of SCID is caused by a defective enzyme, adenosine deaminase (ADA), necessary for the breakdown of purines. Lack of ADA causes accumulation of dGTP. This metabolite is toxic to lymphoid stem cells.

Detection

Standard testing of SCID is not performed for newborns due to the rarity of the disease and the cost of the testing. SCID can be detected by sequencing fetal DNA if a known history of the disease exists. Otherwise, SCID is not detected until about six months of age, usually indicated by recurrent infections. The delay in detection is due to the fact that newborns carry their mother's antibodies for the first few weeks of life and have not yet been exposed to any diseases.

Treatment

The most common treatment for SCID is bone marrow transplantation, which requires matched donors (a sibling is generally best). David Vetter, the original "bubble boy," endured several failed transplantations, and finally passed away because of an unscreened virus, Epstein-Barr, in his newly-transplanted bone marrow from his sister. Today, transplants done in the first three months of life have a high success rate.

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Continuing education activity sponsored by CDC applying public health strategies to primary immunodeficiency diseases: a potential approach to genetic
From Morbidity and Mortality Weekly Report, 1/16/04

EXPIRATION--January 16, 2007

You must complete and return the response form electronically or by mail by January 16, 2007, to receive continuing education credit. If you answer all of the questions, you will receive an award letter for 1.5 hours Continuing Medical Education (CME) credit; 0.15 Continuing Education Units (CEUs); or 2.0 contact hours Continuing Nursing Education (CNE) credit. If you return the form electronically, you will receive educational credit immediately. If you mail the form, you will receive educational credit in approximately 30 days. No fees are charged for participating in this continuing education activity.

INSTRUCTIONS

By Internet

1. Read this MMWR (Vol. 53, RR-1), which contains the correct answers to the questions beginning on the next page.

2. Go to the MMWR Continuing Education Internet site at <http:// www.cdc.gov/mmwr/cme/conted.html>.

3. Select which exam you want to take and select whether you want to register for CME, CEU, or CNE credit.

4. Fill out and submit the registration form.

5. Select exam questions. To receive continuing education credit, you must answer all of the questions. Questions with more than one correct answer will instruct you to "Indicate all that apply."

6. Submit your answers no later than January 16, 2007.

7. Immediately print your Certificate of Completion for your records.

By Mail or Fax

1. Read this MMWR (Vol. 53, RR-1), which contains the correct answers to the questions beginning on the next page.

2. Complete all registration information on the response form, including your name, mailing address, phone number, and e-mail address, if available.

3. Indicate whether you are registering for CME, CEU, or CNE credit.

4. Select your answers to the questions, and mark the corresponding letters on the response form. To receive continuing education credit, you must answer all of the questions. Questions with more than one correct answer will instruct you to "Indicate all that apply."

5. Sign and date the response form or a photocopy of the form and send no later than January 16, 2007, to Fax: 404-639-4198 Mail: MMWR CE Credit

Office of Scientific and Health Communications

Epidemiology Program Office, MS 008

Centers for Disease Control and Prevention

1600 Clifton Rd, N.E. Atlanta, GA 30333

6. Your Certificate of Completion will be mailed to you within 30 days.

Goal and Objectives

This MMWR provides recommendations regarding public health strategies for primary immunodeficiency (PI) diseases. These recommendations were prepared by CDC staff and other specialists in PI diseases after consultation with a multidisciplinary panel. The goal of this report is to familiarize readers with a public health framework for addressing health problems resulting from a group of primarily single-gene disorders. Upon completion of this continuing education activity, the reader should be able to describe 1) the four components of a public health framework; 2) how public health assessment can be applied to PI and other genetic diseases; 3) the framework for evaluating genetic tests, including analytic validity, clinical validity, clinical utility, and ethical, legal, and social considerations; 4) two public health interventions to increase early diagnosis and treatment for genetic diseases (i.e., newborn screening and early clinical recognition); and 5) the key components of an effective health education program for PI diseases.

To receive continuing education credit, please answer all of the following questions.

COPYRIGHT 2004 U.S. Government Printing Office
COPYRIGHT 2004 Gale Group

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