SCID (Severe Combined Immunodeficiency)
Disorder Name: Severe Combined Immunodeficiency
- What is SCID?
- What causes SCID?
- What are the symptoms of SCID?
- What are the treatments for SCID?
- What happens when SCID is treated?
- How is SCID inherited?
- Is genetic testing available?
- What other testing is available?
- Can you test for SCID during a future pregnancy?
- Can other members of the family have SCID or be carriers?
- How many people have SCID?
- Does SCID happen more often in a certain ethnic group?
- Does SCID go by any other names?
- Where can I find more information?
This fact sheet has general information about Severe Combined Immunodeficiency (SCID). Every child is different and some of this information may not apply to your child specifically. Certain treatments may be recommended for some children but not others. If you have specific questions about SCID and available treatments, you should contact your doctor.
WHAT IS SCID?
Severe Combined Immunodeficiency (SCID) is the name for a group of inheritedAcquiring a trait from one’s parents. Most traits, such as eye color or hair color, are inherited from a parent through genes. disorders that cause babies to be born without a working immune systemThis system protects the body from diseases and germs. Through a series of steps called the immune response, the immune system attacks things that infect the body and cause disease.. These disorders are also called primary immune deficiency disorders (PID)A group of conditions caused by genetic errors in the immune system.. Newborns with SCID may seem healthy at first because their mother’s immune system protects them from infections for the first few weeks of life. However, without necessary treatment, common infections and certain types of vaccines can be life threatening to these infants.
The immune system functions with the help of lymphocytesA group of cells that are a part of the immune system. These cells allow the body to remember and recognize previous invaders and help the body destroy them.. Lymphocytes are a type of white blood cellsThe smallest living unit. Cells make up all organs and tissues in multi-cellular organisms, like humans. They can also live independently, as in bacteria and other microorganisms. At a minimum, a cell is surrounded by a membrane, contains DNA at some stage in its life, and is able to replicate itself into two equal parts. made by the bone marrowBone marrow is the tissue that is located around the hollow center of bones. Bone marrow produces new red blood cells..
There are two types of lymphocytes: T cells and B cellsA type of white blood cell that matures in the bone marrow. B cells make antibodies against antigens and create new B cells that remember the antigens old B cells already encountered..
People with SCID have:
- a severe defect in their T cellsA type of white blood cell that matures in the thymus gland. T cells are some of the cells that may be recruited during an immune response., and
- B cells that do not work well.
People with SCID are not able to fight off common infections. They also cannot make antibodies to protect themselves.
WHAT CAUSES SCID?
Genes tell the body how to function. People with SCID can have a change in one or more genesA segment of DNA that contains the instructions to make a specific protein (or part of a protein). Genes are contained on chromosomes. Chromosomes, and the genes on those chromosomes, are passed on from parent to child. Errors in the DNA that make up a gene are called variants and can lead to diseases. that cause SCID. Over 20 different genes are known to cause SCID. VariantsA variant is a change or alteration in a person’s DNA sequence. Variants can happen in genes and affect how the gene functions. There are different types of variants – they can be non-problem causing (benign), disease-causing (pathogenic) or of unknown significance. The term variants is now used in place of the term mutation., or changes to the DNADeoxyribonucleic acid (DNA) is a molecule found in the chromosomes that carries genetic information. DNA is composed of four units (called bases) that are designated A, T, G, and C. The sequence of the bases spell out instructions for making all of the proteins needed by an organism. A gene is a section of DNA that holds the instructions for a specific protein. A change in one or more of the DNA bases making up a gene is called a mutation. Some mutations change the protein instructions and can lead to particular health problems or disorders. Each parent passes half of their chromosomes, and thus half of their DNA instructions, onto their children. It is these instructions that cause certain traits, such as eye or hair color, to be inherited. code in these genes cause the body to have little or no T cells and B cells. This means that the body is not able to defend itself and make the antibodiesAs part of the immune system, antibodies are found in the blood and help to detect and destroy invaders like bacteria and viruses. that are needed to fight infections. This causes common infections, like a cold or flu, to make the child very sick or may even lead to death.
T cells and B cells are normally made by the body. We cannot get them by eating. SCID is not contagious. You cannot get SCID from living with, touching, or spending time with someone who has SCID.
WHAT ARE THE SYMPTOMS OF SCID?
Symptoms of SCID are usually seen in the first year of life. They can be severe and lead to death. It is important to remember that each child with SCID is different and may experience symptoms differently. Symptoms of SCID may include:
- Failure to thrive (not gaining weight, or not growing at a healthy rate)
- Serious and/or life-threatening infections that happen more than once, are not easily treated, and do not get better with medicine. These infections can include:
- Meningitis (brain infection)
- PneumoniaAn infection of the air-sacs (alveoli) of the lungs that causes inflammation (swelling and redness) and fluid build-up. Symptoms include fever, chills, muscle aches and weakness, severe chest pain, cough, shortness of breath and difficulty breathing. It can be dangerous, especially in young children and the elderly. (lung infection)
- Sepsis (blood infection)
- Opportunistic infections (infections that do not cause disease in healthy people). These can include:
- Pneumocystis pneumonia (a specific type of pneumonia)
- Fungal infections
- Viral infections
- Other infections that may happen more frequently include:
- Otitis media (ear infection)
- Sinusitis (sinus infection)
- Skin rashes/infections
- Yeast infections in the mouth or diaper area
- Liver infections
SCID does not affect a person’s intelligence or their ability to learn. Once they get treatment, people with SCID can go to regular school and should be able to reach the same level of education as people without SCID.
An early diagnosis of SCID can lead to early treatment. This can improve the chances for a child to have a good outcome. If it is not treated, SCID will lead to death in infancy or early childhood.
WHAT ARE THE TREATMENTS FOR SCID?
For infants with SCID, the main focus is to prevent infections and treat any active infections.
For prevention, antibiotics and immune globulinA treatment for SCID that gives the body antibodies that would normally be made by the B cells to help fight off infections. It can also be called immunoglobulin or gammaglobulin. may be used. Immune globulin (also called immunoglobulin or gammaglobulin) gives the body antibodies that would normally be made by the B cells. These antibodies help fight infections.
Infants with SCID should also avoid certain types of vaccines called live vaccines. Live vaccines (such as chickenpox, measlesThis is a very contagious type of viral infection. It is also called ‘rubeola.’ Symptoms include red spots and a skin rash, fever, sneezing, nasal congestion, cough, and fatigue., rotavirus, oral polio and BCG and others) contain viruses and bacteria that are weakened and don’t harm children with a healthy immune system. In patients with SCID however, these viruses and bacteria may cause severe, life-threatening infections.
Infants with SCID should avoid things that might expose them to CMV (cytomegalovirus). CMV is a common virus that most people have contracted and carry in their bodies. CMV usually does not cause serious symptoms in healthy infants. However, infants with SCID can get sick from CMV. Some sources of CMV include non-irradiated blood products and possibly breast-milk.
For active infections, aggressive antibiotic, antifungal, and antiviral medicines may be used.
Medicines and immune globulin are only short term treatment options. They can only keep patients with SCID healthy temporarily.
Patients with SCID need more permanent treatments. Treatment options are different depending on which type of SCID your infant has and other factors. Permanent treatment options include:
- Hematopoetic stem cell transplant (HCT) (also known as a bone marrow transplant):
In most cases of SCID, children will need a bone marrow transplant (BMT)When a person does not have enough working red blood cells, they may have a bone marrow transplant. In this surgical procedure, bone marrow is removed from another person (donor) and implanted into the patient. The patient and bone marrow donor must be a genetic match. There are many risks associated with bone marrow transplants.. This is the only treatment that gives children a working immune system that is able to prevent and fight infections
- Enzyme replacement therapy (ERT)A type of therapy that can be used in some metabolic disorders. In people who have certain enzymes either missing or not working correctly, an IV infusion that contains the enzyme can be given. Enzyme replacement therapy is not a cure, but can help with the health problems and symptoms of the disorder.:
Some cases of SCID are caused by a shortage of an enzymeA molecule that helps chemical reactions take place. For example, enzymes in the stomach speed up the process of breaking down food. Each enzyme can participate in many chemical reactions without changing or being used up. called adenosine deaminase (ADA). ADA is found throughout the body but is most active in lymphocytes. A shortage of this enzyme leads to low numbers of T cells and B cells. Enzyme replacement therapy (ERT) with pegademase bovine (PEG-ADA) allows lymphocytes to recover. It may be a long-term treatment option for some children. It is not considered a cure, however, and HCT may still be needed.
- Gene therapyGene therapy is an experimental technique that treats diseases using genes. There are many ways that gene therapy can be done. Sometimes a gene with a disease-causing mutation can be replaced with a healthy gene. Sometimes a gene with a disease-causing mutation can be inactivated or “silenced.” And sometimes a new gene can be put into the body to help fight a disease. Gene therapy is still experimental.:
Gene therapy can be used to treat SCID. Some clinical trials have shown positive outcomes for children, but this form of therapy is still being studied as there are some risks. Gene therapy is still an experimental treatment. Gene therapy is only available as part of a research study and is not FDA-approved yet. Currently, the only way to receive treatment with gene therapy is to participate in a clinical trialClinical trials test the effectiveness of new drugs or treatments. These studies determine how well the treatments work, what risks are associated with them, and whether they work better than the current treatment.. People with SCID must meet strict eligibility criteria and be informed about the potential risks and benefits of being part of a clinical trial. Your medical team can talk to you more about gene therapy.
WHAT HAPPENS WHEN SCID IS TREATED?
Infants with SCID are at risk for fatal infections the moment they are born. So, early diagnosis and treatment are very important. For example, infants with SCID who are treated with BMT before 3.5 months old have a 95% chance of long-term survival and of living a healthy life. BMT treatment after 3.5 months old leads to a 60-70% chance of long-term survival.
With early detectionThe process of testing for a disease in a person who does not show the disease (non-symptomatic or asyntomatic). The goal of screening is to find the disease in its most important stages. and treatment, patients with SCID are more likely to live healthy lives.
HOW IS SCID INHERITED?
SCID is inherited in different ways depending on which gene is causing SCID in your family. The most common way SCID is inherited is called X-linked recessiveThis is a pattern of inheritance in which a gene for a particular trait or disorder is located on the X chromosome. Genes that are ‘recessive’ cause traits or conditions only when they are paired with a dominant gene. Genes usually come in pairs, except on the sex chromosomes in males. Males have one X chromosome that they inherit from their mothers and one Y chromosome that they inherit from their fathers. If a gene on the X chromosome causes a particular trait or disorder, a male will always show that trait or condition as they do not have another gene to cover up its effects. Females usually have a normal copy of that gene on their other X chromosome which covers up the effects of the recessive gene. Some common X-linked recessive disorders include hemophilia, Duchenne muscular dystrophy and color blindness.. SCID can also be inherited in an autosomal recessive manner.
In some families, SCID is not inherited. This means that the baby is the first in the family to have SCID.
X-LinkedA mode of inheritance. X-linked genes are found on the X chromosome. They have a different inheritance pattern than other genes because women have two X chromosomes while men only have one. Any mutation on the X chromosome may not cause a disease in women if the gene on the other chromosome is normal. However, that same mutation on one X chromosome in men will cause the disease because they have no second copy of the gene to compensate. Recessive
The most common type of SCID is inherited in an X-linked recessive manner. In this type of inheritance, the gene is located on the X chromosomeOne of the two chromosomes that are responsible for determining the sex of an organism. The other sex chromosome is called the Y chromosome. Both the X and the Y chromosome contain several genes, only some of which are involved in determining sex. In humans, the X chromosome is the larger of the two sex chromosomes. Females usually have two X chromosomes and males usually have one X chromosome and one Y chromosome., one of the sex chromosomesA strand of DNA contained within a cell. Each chromosome contains many thousands of genes. In humans, there are a total of 46 chromosomes, half of which come from each parent. The combined total of all chromosomes in a cell is the genome.. The gene that causes X-linked SCID is call IL2RG. Genes usually come in pairs, with each parent giving one copy to their child. The sex chromosomes, however, are different.
A male inherits one X chromosome from his mother, and one Y chromosomeOne of the two sex chromosomes that is responsible for determining the sex of an organism. The other sex chromosome is called the X chromosome. Both the X and the Y chromosome contain several genes, only some of which are involved in determining sex. In humans, the Y chromosome is the smaller of the two sex chromosomes. Most females have two X chromosomes and most males have one X chromosome and one Y chromosome. from his father. A female inherits two X chromosomes, one from each parent. When a female has a non-working copy of the gene on one of her X chromosomes, she will not have SCID. This is because she has a second, working copy of the gene on her other X chromosome.
A male with a non-working IL2RG gene for SCID on his X chromosome will have SCID. This is because he does not have a second X chromosome with a working IL2RG gene. Because they only have one copy of the IL2RG gene, it is more common for males to have X-linked recessive SCID than females.
If a mother has one non-working IL2RG gene, she is called a carrier. For carriersA person who has one copy of a gene mutation for a particular autosomal recessive disorder (remember genes come in pairs). Carriers are not affected by the disorder. However, they can pass on the gene variant to their children. Children who inherit two such gene variants will be affected by the disorder. The term variants is now used in place of the term mutation., there is a 50% chance that each male pregnancy will have SCID. For carriers, there is a 50% chance that each female pregnancy will be a carrier, like her mother.
A father passes his Y chromosome to his sons and his X chromosome to his daughters. Therefore, if a father has SCID, none of his sons will have SCID and all of his daughters will be carriers.
Autosomal RecessiveMost of the metabolic disorders that can be detected by newborn screenings are inherited in an “autosomal recessive” pattern. Autosomal recessive conditions affect both boys and girls equally. How autosomal recessive inheritance works: Everyone has a pair of genes for each enzyme in the body. A separate pair of genes is responsible for making each enzyme. A person with a metabolic disorder has one enzyme that is either missing or not working properly. The problem is caused by a pair of “recessive” genes that are not working correctly. They do not make the needed enzyme. A person has to have two non-working “recessive” genes in order to have an autosomal recessive metabolic disorder. A person with an autosomal recessive disorder inherits one non-working gene from his or her mother and the other from his or her father. The parents are called carriers for that condition. Parents of children with a metabolic disorder rarely have the disorder themselves. Instead, for that pair of genes, each parent has one that is working correctly and one that is not working (called the “recessive” gene). People with a single non-working gene are called carriers. If one gene of the pair is working correctly, it makes up for the recessive non-working gene. Therefore, carriers usually will not have the condition.
Some types of SCID are inherited in an autosomal recessive manner. There are many different genes that cause autosomal recessive SCID. This type of inheritance affects both boys and girls equally.
In autosomal recessive geneticRelating to (or due to) genes and heredity or the field of studying genes and heredity. conditions, we think about the genes other than those inherited on the sex chromosomes. These are the same in both boys and girls. Everyone has pairs of these genes, one from mom and one from dad.
Many genes help make our immune system work the way it should. In children with autosomal recessive SCID, a pair of genes does not work correctly. These children inherit one copy of the non-working gene from each parent.
Parents of children with autosomal recessive SCID are rarely affected, themselves. Instead, each parent has one non-working gene for SCID. They are called carriers. Carriers do not have SCID because their other copy of the gene works correctly.
When both parents are carriers, there is a 25% chance in each pregnancy for the child to have SCID. There is a 50% chance for the child to be a carrier, just like the parents. There is a 25% chance for the child to have two working genes.
Genetic counseling is available to families who have children with SCID. Genetic counselors can answer questions about how SCID is inherited, choices during future pregnancies, and how to test other family members. Ask your doctor about a referral to a genetic counselorThese are health care providers who have special training in genetic conditions. They help families understand genetic disorders and how they are passed down. Genetic counselors offer information and support to people who have genetic conditions in their families or are concerned that they may have a child with an inherited disorder..
IS GENETIC TESTING AVAILABLE?
Genetic testing for SCID is available. Over 20 different genes can cause SCID. Genetic testing, also called DNA testing, looks for changes called variants in the genes that cause SCID. DNA testing is typically done on a blood sample.
Even if the genetic cause of SCID in your baby is unknown, he or she can still get therapy for SCID. This information can also be helpful in carrier or prenatal testing, discussed below.
WHAT OTHER TESTING IS AVAILABLE?
Newborn ScreeningA screening test that looks for different disorders using a small sample of blood taken from a newborn’s heel. A positive or abnormal newborn screening result means that there are slight differences that were found in the baby’s blood, and further testing is needed to figure out if the baby has a metabolic disorder.
Newborn screeningThe process of testing for disease in a person who does not show signs of having the disease (nonsymptomatic or asymptomatic person). The goal of screening is to catch the disease in its early stages. for SCID is done in all states in the United States. A blood spot from a needle prick on a baby’s heel is used to screen for many different conditions. Newborn screening for SCID is done by looking for T cell receptor excision circles (or TRECs for short). TRECs are found in every healthy newborn’s blood. They are present when T cells are being produced. Since babies with SCID have few to no T cells, they also have few to no TRECs in their blood.
If a baby has a positive result on the initial SCID newborn screen, it does not mean that he or she has SCID. Low levels of TRECs in the blood can also be caused by prematurity, other less severe immune disorders, or other syndromes. It is also possible for a baby to have a positive screening result, but have a normal immune system. A positive newborn screening result means that further testing must be done to confirm or rule out SCID.
When a parent or both parents are known to be carriers of SCID, newborn screening results are not enough to rule out SCID in a newborn baby. In this case, diagnostic testing should be done, as well as newborn screening.
Two types of testing are used to confirm SCID. These tests are called a complete blood count (CBC) and flow cytometryA laboratory technique used to count cells, sort cells, and learn about cells one at a time. This test can give information about the amounts of the different types of white bloods cells, such as T cells and B cells.. These need a blood sample to measure the amount of lymphocytes in an infant’s blood. DNA testing may also be done.
Infants who are confirmed to have SCID will then be referred to a pediatric immunologist or infectious disease specialistA doctor who has special training in the diagnosis and treatment of infectious diseases.. The specialist will make recommendations for further treatment and management.
CAN YOU TEST FOR SCID DURING A FUTURE PREGNANCY?
Prenatal genetic testing for SCID is only available if a genetic cause has already been identified in the family. If a genetic cause has been identified, DNA from the fetus can be removed and tested. The sample for this testing is obtained by either CVS or amniocentesisThis is a test done during pregnancy. A needle is used to remove a small sample of fluid from the sac around the fetus. The sample can be used to test for certain genetic disorders in the fetus. Amniocentesis to test for genetic conditions is usually done between 13 and 20 weeks of pregnancy..
Parents may choose to have testing during pregnancy or wait until birth to have the baby tested. Parents may also choose to use assisted reproductive techniques to decrease the chance that their future children would have SCID. A genetic counselor can talk to you about your choices and answer questions about prenatal testing or testing your baby after birth.
CAN OTHER MEMBERS OF THE FAMILY HAVE SCID OR BE CARRIERS?
If they are healthy and developing normally, older brothers and sisters of a baby with SCID are unlikely to have SCID. In some cases, siblings should also be evaluated for SCID. Talk to your doctor or genetic counselor if you have questions about your other children.
Brothers and sisters who do not have SCID still have a chance of being carriers, like their parent(s). Each healthy brother and sister have a chance of being a carrier for SCID. Except in special cases, carrier testing should only be done in people over 18 years of age.
It is important for other family members to be told that they could be carriers. There is a chance they are also at risk to have children with SCID.
HOW MANY PEOPLE HAVE SCID?
The true incidence of SCID is unknown. It is estimated that about 1 in every 58,000 live births in the United States is a baby with SCID.
DOES SCID HAPPEN MORE OFTEN IN A CERTAIN ETHNIC GROUP?
It seems that one of the autosomal recessive forms of SCID happens slightly more often in people of Native American ethnicity. In general, SCID can affect people of all ethnic backgrounds.
DOES SCID GO BY ANY OTHER NAMES?
SCID is also sometimes called:
- Severe combined immune deficiency
- Severe mixed immunodeficiency syndromeA group of symptoms and clinical findings that, when found together, make up a particular condition or disease.
- Primary immune deficiency
WHERE CAN I FIND MORE INFORMATION?
Immune Deficiency Foundation
The Jeffrey Modell Foundation
National Human GenomeAll of the genetic material (DNA) contained in a full set of chromosomes in an organism. In humans, about three billion base pairs make up our genome. Research Institute
National Marrow Donor Program
American Academy of Allergy, Asthma and Immunology
|Reviewed by:||HI, CA, OR, and WA metabolic specialists|
|Review date:||June 4, 2014
June 12, 2020
March 19, 2023
|Update on:||March 19, 2023|
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