Severe Combined Immunodeficiency
Severe combined immunodeficiency (SCID), also known as Swiss-type agammaglobulinemia, is a rare genetic disorder characterized by the disturbed development of functional T cells and B cells caused by numerous genetic mutations. It is a type of primary immune deficiency which causes life-threatening problems with immune system.
Pathophysiology of Severe combined immunodeficiency
In a developing baby, the immune system starts in the bone marrow. Stem cells there can become any of three different types of blood cells –
• Red blood cells
• White blood cells
White blood cells protect the body from infections and foreign invaders. There are different kinds of white blood cells, including lymphocytes. Lymphocytes come in two main types –
These cells are key to fighting infections –
• T cells identify, attack and kill invaders.
• B cells make antibodies that remember an infection and are ready in case the body is exposed to it again.
SCID is a “combined” immunodeficiency because it affects both of these infection-fighting white blood cells.
As because the immune system doesn’t work as it should, it can be difficult or impossible for it to battle the germs – viruses, bacteria and fungi – that causes infections.
Babies with SCID may seem well at birth and for the first few weeks of life.This is because they are partly protected by antibodies passed from mother to baby across the placenta during the last few months of pregnancy.
Symptoms of SCID usually start within the first year of a child’s life. usually the child will have many serious infections, life-threatening infections or both. The infections are not easily treated and medicines to treat the infections don’t work well. Common infections include –
• Repeated ear infections
• Oral thrush ( a type of yeast infections in the mouth)
• Diaper rashes
• Blood infection
• Chronic Diarrhoea
• Chronic skin infections
• Liver infection (hepatitis)
• Problem in weight gain
SCID is an inherited condition, meaning it is passed on in families in the same way as physical characteristics, such as eye colour, are passed from parent to child. It is caused by a mistake (or mutation) in a child’s genetic make-up.
The most common type is caused by a problem in a gene found on the X chromosome and affects only males. Females can be carriers of the condition, but because they also inherit a normal X chromosome, their immune system can fight infections. Males, though, have only one X chromosome, So if the gene is abnormal, the disease appears.
In infants affected by SCID, a genetic mutation results in the absence or malfunction of a protein that is necessary for normal development or function of the immune system. Many different genes can be affected, each causing a different type of SCID. The names given to the different types of SCID are based on the particular protein or gene that is affected.
Some of the more frequently encountered types include –
• Common gamma chain deficiency
• Adenosine deaminase (ADA) deficiency
• JAK 3 kinase deficiency
• MHC class II deficiency
• Recombinase activating gene (RAG) deficiency
It is important to know the exact cause –
• because is some conditions there may be specific treatment available
• to allow accurate genetic counselling for future pregnancies
• Doctors use a simple blood test to screen newborns for many conditions that could cause health problems. Newborn screening for SCID makes early diagnosis possible.
• Babies with a newborn screen suggestive of SCID usually are referred to a doctor specializing in immune deficiencies. The doctor will order other blood tests and possibly genetic testing.
• Parents who have a child with SCID or a family history of immunodeficiency might want to consider genetic counselling and early blood testing.
Early diagnosis can lead to quick treatment and a better outcome.
Severe combined immunodeficiency (SCID) is a pediatric emergency. Without treatment, babies are not likely to survive past their first birthday. The most common treatment is a stem cell transplant (also called a bone marrow transplant). This means the child receives stem cells from a donor. The hope is that these new cells will rebuild the child’s immune system.
The most successful stem cell transplants use cells donated by a sibling. Sometimes, a parent’s Stem cells are a match. If no family members are suitable donors, doctors may use stem cells from an unrelated donor. Some children with SCID may need chemotherapy before their transplant.
A baby with SCID who gets a stem cell transplant in the first few months of life, before getting any infections, is likely to survive.
Besides medicines and therapies to help prevent infections, other precautions which should be taken are as follows-
• Children with SCID should be placed in isolation to help prevent the spread of infection.
• Children with SCID should not get live vaccines even in weakened vaccine form. As introducing a virus or bacteria to a child with SCID can be dangerous. The examples of such vaccines are chickenpox vaccine, measles, mumps and rubella (MMR) vaccine, rotavirus vaccine, Oral polio, BCG and Flumist vaccines.
• Children may be stopped from breastfeeding until breast milk is checked for a virus that may cause infection.
• Children with SCID who need blood transfusions must get blood that has been specially treated to help prevent transfusion-related complications.
What caregivers need to do?
While your child is being evaluated for SCID, help reduce the risk of infection by –
• limiting visitors
• keeping your baby away from anyone with a cold or infection
• avoiding public places
• making sure that caregivers wash their hands well before touching your baby
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