Specific antibody deficiency (SAD) is an immune system disorder. It occurs when you have normal levels of antibodies but an insufficient immune response to certain types of bacteria.
Antibodies, also called immunoglobulins, are Y-shaped proteins produced by your immune system that help identify foreign substances in your body and tell other immune cells to attack them.
Your body produces
People with SAD have typical total antibody levels, but a defect in IgG levels that prevents them from mounting an effective immune response to polysaccharide antigens. These are specific sugar-containing markers found on the surface of some bacteria.
Imagine certain bacteria have a sign on them that says, “destroy me.” Normally, IgG recognizes this and attaches itself to the bacteria. But in people with SAD, it’s as if the sign is in a language your antibodies can’t understand.
SAD is also referred to as impaired antibody response to polysaccharide antigens or selective antibody deficiency.
People with SAD have a higher risk of developing certain types of bacterial infections, particularly those affecting the lungs, ears, and sinuses.
Keep reading to learn more about SAD, including its causes, treatments, and more.
SAD is the eighth most common primary immunodeficiency in the world, which means it weakens the immune response and isn’t caused by another underlying condition.
Researchers aren’t entirely sure what causes SAD. No clear pattern of inheritance has been observed, but it’s thought that genetic mutation plays a role in its development.
Several theories have been proposed regarding its development. One of the more prevalent theories is that it may be linked to a defect in a type of immune cell called splenic marginal zone B cells, which are found in the spleen.
SAD itself doesn’t cause any symptoms, but it increases the risk of infections. Children or adults with SAD may experience recurrent:
How common is SAD?
SAD is a relatively rare condition. The prevalence isn’t well known, but it has been reported to range from 11% to 60% of cases in some studies examining people with unexplained bacterial infections.
Researchers continue to investigate the potential causes and treatment options.
SAD can either be classified as transient or permanent:
- Transient: Some children diagnosed with SAD eventually outgrow it.
- Permanent: SAD diagnosed in adults is more likely to be permanent, or chronic, which means long-term management may be required.
In some cases, people with other types of recurrent infections or immunodeficiencies may have SAD. For instance, a 2017 study in 596 people with chronic rhinosinusitis found that 40% of individuals had SAD.
In rare cases, SAD may progress to a broader type of immunodeficiency called common variable immune deficiency (CVID), which affects
It’s a good idea to connect with a child’s pediatrician if they’ve frequently been getting ill. Recurrent infections don’t always mean that they have an immunodeficiency, but it’s often the first sign.
Adults should also connect with a primary care doctor if they experience frequent ear, sinus, or lung infections.
Pediatricians and PCPs can examine symptoms and, if necessary, provide a referral to speak with an immunologist, who is a specialist in the immune system.
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SAD can only be diagnosed in children older than 2 years old because a similar type of immunodeficiency is normally seen in younger children.
Doctors might suspect SAD in children or adults with recurrent infections. A doctor usually starts the diagnostic process by:
- reviewing your or your child’s medical history
- performing a physical examination
- asking you or your child about their symptoms
If they suspect an immune problem, they’ll likely order an immunoglobulin test or other blood tests to measure your antibody levels and look for bacteria like tetanus, diphtheria, or Streptococcus pneumoniae. Low total antibodies suggest a broader type of immunodeficiency, like CVID.
If low levels of antibodies to Streptococcus pneumoniae are found in your blood, a doctor may administer a pneumococcal vaccine. Levels of antibodies will be measured in your blood 4 to 6 weeks after the injection to determine your response. A poor response may indicate SAD.
Treatment for SAD depends on the severity of the immunodeficiency and how frequently and severely you’ve been getting sick.
Some studies suggest that prophylactic antibiotics, meaning administering antibiotics before an infection occurs, may be beneficial to certain individuals, especially children who may outgrow SAD.
Some people may receive immunoglobulin replacement therapy. This therapy is often short-term for children and long-term for adults. It involves injecting healthy antibodies into the bloodstream to help strengthen the immune system.
A cure hasn’t been developed for SAD, but some children seem to outgrow it.
Taking basic precautions for avoiding illness is particularly important for people with immunodeficiency. This can include:
- frequently washing your hands
- minimizing contact with people with active respiratory illness
- considering wearing a mask in public spaces
Receiving conjugate vaccines that cover a wide range of diseases may also help prevent disease for some people with SAD. These vaccines involve artificially attaching a protein to the outer shell of bacteria in the vaccine so your body can better detect them and mount an immune response.
The outlook for people with SAD is often good. Children often seem to outgrow it, but according to the Immune Deficiency Foundation, this is less likely in adults.
Some studies have found that AD was linked to greater severity of asthma or lower-airway disease, but not all studies have come to this conclusion.
A healthcare professional can help you better understand your outlook if you have SAD.
SAD is an immune disorder in which the immune system fails to mount an effective response to certain types of bacteria. People with SAD are at an increased risk of certain types of infections, including sinus and ear infections.
Some children with SAD outgrow it, and many have a good outlook. Researchers are still investigating exactly what causes SAD and how to best treat it.