The Silent Threat to the Immune System: What You Need to Know About SCID

Severe combined immunodeficiency (SCID)is a rare condition that causes babies to be born with little or no immunesystem.[1]

Severe combined immunodeficiency (SCID) is one of themost severe types of primary immunodeficiency (PI).[2] Babiesborn with SCID lack white blood cells called T cells. Because T-cells arecritical for B-cells to work, these babies will have problems with the types ofinfections B-cells are supposed to handle, too. That’s what the “combined” inSCID’s name comes from — missing a combination of these important defense cells.¹Immunodeficiency disorders suppress your immune system and keep it fromworking properly. Immunodeficiency disorders weaken your body’s natural abilityto defend itself.¹

Babies born with SCID can’t fight off infections, evencommon illnesses that are usually not severe or dangerous. If it’s not treated,SCID is fatal in most children within a year or two.¹ However, if achild with SCID is diagnosed and treated within the first few months of lifebefore any serious infections develop, their long-term survival rate is morethan 90%.²

How is SCID diagnosed?

Babies born with SCID appear healthy at birth but areunable to fight infections.² Providers diagnose SCID with a bloodtest. Your provider will take a small blood sample from your baby right afterbirth (usually from your child’s heel).¹ The newborn screening bloodtest can show if a baby has a low number of T cells, a sign that a baby mayhave SCID.²

What are SCID symptoms?

SCID may not cause any symptoms you can notice. If itdoes, they usually include:

·       Yourchild not gaining weight at a typical healthy rate.

·       Chronicdiarrhea.

·       Frequent,severe infections.¹

Your baby’s immune response to infections will bedramatically reduced or absent. That means your child will be much more likelythan usual to get sick. And when they do, their symptoms will be much moresevere than usual.¹

Babies with SCID have a higher risk for all types ofinfections, including:

·       Bacterialinfections.

·       Viralinfections.

·       Fungalinfections.

·       Parasiticinfections.

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Any illness can cause severe symptoms, but some types ofinfections are more common in babies with SCID, including:

·       Yeastinfections (thrush or diaper rash).¹

·       Chickenpox.¹

·       Coldsores (herpes simplex).¹

·       Earinfections.¹

·       Pneumonia.¹

·       Meningitis.¹

What causes SCID?

Variants in at least 20 different genes can cause SCID.Although the types of SCID vary with respect to the cause of theimmunodeficiency, their laboratory findings, and their pattern of inheritance,infants with any type of typical SCID have severe deficiencies in both T celland B cell function. The treatment approach will vary with SCID type, so it’simportant to know what kind of SCID an individual has.²

How is SCID treated?

In all types of SCID, individuals have a severe reductionin the number of T cells, which are a type of white blood cell. Treatments forSCID like hematopoietic stem cell transplant (HSCT) and gene therapy fix theindividual’s immune system by replacing their blood-forming cells, which allowstheir body to make functional T cells. In the case of enzyme replacementtherapy (ERT), which is only an option for ADA-SCID, the treatment provides aworking version of the ADA protein, which breaks down the toxin that killsthese individuals’ T cells.^2
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If a child with SCID is diagnosed and treated within thefirst few months of life, before any serious infections develop, theirlong-term survival rate is more than 90%. Once an infection develops in a babywith SCID, it may reduce the effectiveness of treatment or cause organ ortissue damage that treatment cannot undo.²

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