HomeGeneticsConditionBare lymphocyte syndrome type II
Back to Condition
Bare lymphocyte syndrome type II
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Bare lymphocyte syndrome type II

Bare lymphocyte syndrome type II (BLS II) is a severe inherited immune system disorder, a form of combined immunodeficiency, characterized by a lack of immune protection against bacteria, viruses, and fungi, leading to life-threatening infections and typically early childhood mortality without treatment.

Overview

Bare lymphocyte syndrome type II (BLS II) is an inherited disorder of the immune system categorized as a form of combined immunodeficiency (CID). People with BLS II lack virtually all immune protection from bacteria, viruses, and fungi. They are prone to repeated and persistent infections that can be very serious or life-threatening. These infections are often caused by "opportunistic organisms" that ordinarily do not cause illness in people with a normal immune system.

BLS II is typically diagnosed in the first year of life. Most affected infants have persistent infections in the respiratory, gastrointestinal, and . Because of the infections, affected infants have difficulty absorbing nutrients (malabsorption), and they grow more slowly than their peers. Eventually, the persistent infections lead to organ failure. Without treatment, individuals with BLS II usually do not survive past early childhood.

In people with BLS II, infection-fighting white blood cells (lymphocytes) are missing specialized proteins on their surface called MHC class II proteins, which is where the condition got its name. Because BLS II is the most common and best studied form of a group of related conditions, it is often referred to as simply bare lymphocyte syndrome (BLS).

Frequency

BLS II is a rare condition. At least 100 cases have been reported in the medical literature. While BLS II has been found in several populations throughout the world, it appears to be especially prevalent in the Mediterranean region and North Africa.

Causes & Risk Factors

BLS II is caused by mutations in the CIITA gene, RFX5 gene, RFXANK gene, or RFXAP gene. Each of these genes provides instructions for making a protein that plays a role in controlling the activity (transcription) of genes called MHC class II genes. Transcription is the first step in the production of proteins, and the CIITA, RFX5, RFXANK, and RFXAP proteins are critical for the production of from these genes.

The RFX5, RFXANK, and RFXAP proteins come together to form the regulatory factor X (RFX) complex, which attaches (binds) to specific regions of DNA involved in the regulation of MHC class II gene activity. The CIITA protein interacts with the RFX complex and brings together other proteins that turn on gene transcription, leading to the production of MHC class II proteins.

MHC class II proteins play an important role in the body's immune response to foreign invaders, such as bacteria, viruses, and fungi. To help the body recognize and fight infections, MHC class II proteins on lymphocytes bind to fragments of proteins (peptides) from foreign invaders so that other specialized immune system cells can interact with them. When these immune system cells recognize the peptides as harmful, they trigger the lymphocytes to launch immune responses to get rid of the foreign invaders.

Mutations in the CIITA, RFX5, RFXANK, or RFXAP gene prevent transcription of MHC class II genes, which leads to an absence of MHC class II proteins on the surface of certain lymphocytes. Lack of these proteins on lymphocytes impairs the body's immune response to bacteria, viruses, and fungi, leading to persistent infections in individuals with BLS II syndrome.

Genes Associated with Bare Lymphocyte Syndrome Type II

  • CIITA
  • RFX5
  • RFXANK
  • RFXAP

Inheritance

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Other Names

  • Bare lymphocyte syndrome type 2
  • BLS type II
  • Major histocompatibility complex class II deficiency
  • MHC class II deficiency
  • SCID due to absence of class II HLA antigens
  • SCID, HLA class 2-negative
  • SCID, HLA class II-negative
  • Severe combined immunodeficiency due to absent class II human leukocyte antigens
  • Severe combined immunodeficiency, HLA class II-negative

Frequently Asked Questions

Parents should be alert for recurrent, severe, or unusual infections that do not respond well to standard treatments. These often include persistent respiratory infections (like pneumonia or bronchitis), chronic diarrhea, skin rashes, and oral thrush. Infants may also show signs of failure to thrive, such as poor weight gain and slow growth, due to malabsorption caused by gastrointestinal infections.
The only curative treatment for Bare Lymphocyte Syndrome Type II is hematopoietic stem cell transplantation (HSCT), often referred to as a bone marrow transplant. This procedure replaces the faulty immune system cells with healthy ones. Without HSCT, the prognosis is very poor, with most individuals not surviving past early childhood due to overwhelming infections. With successful HSCT, the prognosis significantly improves, allowing individuals to develop a functional immune system and live longer, healthier lives, though long-term monitoring is still necessary.
Diagnosis usually begins with a suspicion based on recurrent severe infections and failure to thrive. Blood tests will show a lack of MHC class II proteins on the surface of immune cells, particularly B lymphocytes, which is a hallmark of the condition. Further confirmation comes from genetic testing to identify mutations in the genes responsible for MHC class II expression, such as CIITA, RFXANK, RFX5, or RFXAP.
Bare Lymphocyte Syndrome Type II is inherited in an autosomal recessive pattern. This means that both parents must be carriers of a mutated gene (each having one copy) to have an affected child. Carriers typically do not show symptoms. If both parents are carriers, there is a 25% chance with each pregnancy that their child will inherit two copies of the mutated gene and develop BLS II, a 50% chance the child will be a carrier, and a 25% chance the child will inherit two normal copies of the gene. Genetic counseling is highly recommended for families with a history of BLS II to understand these risks and discuss options like prenatal diagnosis.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

kontakt@hittavard.se

Ⓒ 2024. Alla rättigheter förbehålls av juxt ab

Sök
Om ossVillkor och policyVanliga frågorKontakta oss