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Bare lymphocyte syndrome type 2

Bare lymphocyte syndrome type 2




Overview

 Bare lymphocyte syndrome type II (BLS II), also known as Major Histocompatibility Complex (MHC) class II deficiency, is a rare autosomal recessive form of Severe Combined Immunodeficiency (SCID). It occurs when the body fails to express MHC class II molecules (such as HLA-DR, HLA-DQ, and HLA-DP) on the surface of antigen-presenting cells.

Symptoms

Symptoms usually appear within the first year of life:

• Recurrent and Severe Infections: Frequent bacterial, viral, fungal, and parasitic infections—especially in the respiratory tract (pneumonia, bronchitis, sinusitis), gastrointestinal tract, and urinary tract.

• Digestive Issues: Chronic or persistent diarrhea, nutrient malabsorption, and gastrointestinal infections (such as Cryptosporidium).

• Growth and Developmental Delays: Failure to thrive, slow physical growth, and malnutrition.

• Oral and Skin Conditions: Chronic mucocutaneous candidiasis (oral thrush) and persistent skin or herpesvirus infections.

• Liver and Biliary Complications: Chronic hepatitis, cholangitis, or sclerosing cholangitis.

• Autoimmune Phenomena: Autoimmune cytopenias and related inflammatory signs.

Causes

Mutations in any of the following four genes prevent the transcription of MHC class II molecules:

• CIITA (Class II transactivator)

• RFX5 (Regulatory factor X5)

• RFXANK (Regulatory factor X ankyrin repeat-containing)

• RFXAP (Regulatory factor X-associated protein)

Diagnosis

Flow Cytometry: The hallmark diagnostic test checks for the absence of MHC class II molecules (such as HLA-DR, HLA-DQ, and HLA-DP) on the surface of professional antigen-presenting cells (like B cells, monocytes, and dendritic cells).

• Immunological Assessment (Blood Tests):

• Shows a severe reduction in CD4+ T-cell counts (with a normal or near-normal total number of T cells).

• Reveals hypogammaglobulinemia (low levels of immunoglobulins like IgG, IgA, or IgM) and poor or absent specific antibody responses to vaccines.

• Demonstrates a weak or absent T-cell proliferative response to mitogens or foreign antigens.

• Genetic Testing: Identifies loss-of-function mutations in one of the specific regulatory genes responsible for transcribing MHC class II molecules: CIITA, RFX5, RFXANK, or RFXAP.

• Clinical Evaluation: Doctors evaluate early-infancy symptoms such as severe recurrent respiratory and gastrointestinal infections, protracted diarrhea, and failure to thrive

Treatment

1. Curative Therapy

• Allogeneic Hematopoietic Cell Transplantation (HCT): Replaces the patient's faulty immune system with healthy stem cells from a donor.

• Timing: Transplant outcomes are significantly better when performed early in life (ideally within the first two years) before severe, irreversible organ damage or chronic infections occur.

• Modifications: Modern protocols use reduced-toxicity or reduced-intensity conditioning regimens, improved T-cell depletion, and supportive care to lower transplant-related complications and graft-versus-host disease (GVHD).

2. Supportive and Pre-Transplant Management

Before a transplant can take place—or for patients who cannot undergo transplantation immediately—aggressive supportive care is critical to manage life-threatening vulnerabilities:

• Antimicrobial Prophylaxis: Preventive antibiotics, antifungals, and anti-parasitic medications to ward off opportunistic pathogens like Pneumocystis jirovecii.

• Immunoglobulin Replacement Therapy (IVIG): Infusions of antibodies to help make up for severe hypogammaglobulinemia (low levels of infection-fighting antibodies).

• Infection Control: Rapid, aggressive treatment of active bacterial, viral, or fungal infections.

• Vaccination Restrictions: Avoidance of live vaccines, which can cause severe or fatal infections in immunocompromised individuals.

Type of Doctor Department : A pediatric or adult clinical immunologist / allergist or a medical geneticist

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