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Bare lymphocyte syndrome type I (BLS I)

Bare lymphocyte syndrome type I (BLS I) 



Overview

Bare lymphocyte syndrome type I (BLS I) is a rare, inherited primary immunodeficiency caused by a lack of Major Histocompatibility Complex (MHC) class I proteins on cell surfaces, leading to recurrent, severe bacterial infections, often in the lungs and airways. It is caused by genetic mutations, notably in 

or genes, resulting in severe infections starting in childhood. According to the Immune Deficiency Foundation, management often requires diligent infection control and antibiotic treatment.

Symptoms

Recurrent Respiratory Infections: Frequent, severe bacterial infections in the lungs and airways (bronchitis, pneumonia, sinusitis) that often start in childhood.

Bronchiectasis: Chronic lung damage, a common result of recurrent respiratory infections.

Skin Lesions/Ulcers: Development of necrotic skin ulcers, often appearing in adolescence or young adulthood, typically on the face, arms, and legs.

Chronic Infections: Increased susceptibility to bacteria, leading to persistent, hard-to-treat infections.

Mild or No Symptoms: Some individuals with BLS I may show no symptoms, or have a milder presentation.

Causes

TAP1 or TAP2 Gene Mutations: The most common cause, these mutations (often homozygous or compound heterozygous) disrupt the TAP transporter complex. This prevents peptides from moving into the endoplasmic reticulum, stalling MHC class I assembly.

TAPBP (Tapasin) Gene Mutation: Though rarer, mutations in the gene encoding Tapasin can also cause this syndrome.

Autosomal Recessive Inheritance: The defect is inherited, meaning an affected individual inherits two mutated copies of the gene, one from each parent.

Diagnosis

Flow Cytometry: Shows severely reduced or absent MHC class I molecules (HLA-A, B, C) on the surface of peripheral blood lymphocytes.

Genetic Testing: Identifies mutations in TAP1, TAP2, or TAPBP genes, which are responsible for antigen processing and peptide loading, according to the Wikipedia article and PubMed Central (PMC).

Immunological Studies: Generally reveals normal levels of immunoglobulin and T/B cell counts, distinguishing it from type II.

Clinical Presentation: Patients often present in childhood with recurrent bacterial infections of the respiratory tract (bronchiectasis) and sometimes necrotic granulomatous skin lesions.

Treatment

Prophylactic/Active Antibiotics: Ongoing antibiotic treatments are essential to prevent and treat severe infections, particularly in the respiratory tract.

Supportive Therapy: Immunoglobulin replacement therapy (IVIG) may be used to manage susceptibility to infections, though it is more typically associated with Class II deficiencies.

Management of Granulomatous Lesions: In cases involving skin issues (similar to those seen in TAP1/TAP2 deficiency), medications like steroids (e.g., prednisolone) have shown success in decreasing inflammation, with potential transitions to thalidomide for long-term management.

Investigational/Stem Cell Approaches: Unlike type II, hematopoietic stem cell transplantation (HSCT) is not typically the standard primary treatment for Type I, but it may be considered in specialized cases

Type of Doctor Department : A pediatric or adult immunologist

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