Immunoglobulin G4 (IgG4) deficiency is a rare immune system condition characterized by insufficient IgG4 antibody levels. This deficiency impairs the body’s ability to fight certain infections, leading to various health concerns.
Understanding IgG4 and Its Deficiency
Immunoglobulin G (IgG) is the most prevalent antibody in human blood, comprising 75-80% of the total antibody pool. It has four subclasses: IgG1, IgG2, IgG3, and IgG4. IgG4 is the least abundant, typically making up 3-6% of total IgG, and has unique functional characteristics.
IgG4 is thought to have an immune-inhibitory function. It helps prevent excessive inflammation and tissue damage, especially during chronic antigen exposure or parasitic infections. IgG4 deficiency is a primary immunodeficiency, meaning it results from an inherent problem within the immune system.
Recognizing the Signs
The signs and symptoms of IgG4 deficiency vary among individuals, often depending on affected organs or systems. A common sign is increased susceptibility to recurrent infections, especially in the respiratory tract. These include ear infections, sinus infections, bronchitis, and pneumonia, frequently caused by encapsulated bacteria like Streptococcus pneumoniae and Haemophilus influenzae.
Beyond infections, other health issues may include chronic diarrhea, asthma, and adverse food reactions. Some individuals also present with autoimmune disorders, where the immune system mistakenly attacks the body’s own tissues.
Confirming a Diagnosis
Diagnosing IgG4 deficiency requires a comprehensive evaluation by a healthcare professional, as symptoms can overlap with many other conditions. The process typically includes blood tests to measure immunoglobulin levels, including IgG4. While low serum IgG4 levels are part of the picture, an isolated low IgG4 level alone is insufficient for diagnosis, as healthy adults can sometimes have undetectable levels.
A definitive diagnosis often requires additional evaluation. This includes demonstrating a poor antibody response to specific vaccines, alongside a documented history of recurrent infections. Imaging studies like CT scans or MRIs may also assess potential organ involvement and rule out other diseases that mimic IgG4 deficiency, including certain cancers.
Managing the Condition
Managing IgG4 deficiency focuses on reducing the frequency and severity of infections and addressing any associated conditions. If clinically indicated, immunoglobulin replacement therapy (IgRT) is a standard treatment for antibody deficiencies. This therapy provides the body with functional antibodies derived from donated human plasma.
IgRT can be administered in two main ways: intravenously (IVIG) or subcutaneously (SCIG). IVIG infusions are typically given every 3 to 4 weeks, delivering a rapid increase in antibody levels, though levels can fluctuate between doses. SCIG involves slower, more frequent injections, often weekly, leading to more stable antibody levels over time. The choice between IVIG and SCIG depends on individual patient factors and preferences, and both methods have demonstrated similar effectiveness in treating primary immunodeficiency.
Long-Term Outlook
With a proper and timely diagnosis, along with consistent medical management, many individuals living with IgG4 deficiency can maintain a good quality of life. Long-term management typically involves ongoing medical care and regular monitoring by specialists, such as immunologists. Adherence to prescribed treatment plans, including immunoglobulin replacement therapy if indicated, is important for preventing complications and managing symptoms effectively.
While some patients may experience periods of remission, others might require continuous treatment to keep the condition under control. Early diagnosis can help prevent irreversible organ damage that may occur if the condition goes untreated or undertreated. Patient education and active engagement in self-management also play a role in achieving positive long-term outcomes.