How is SP-B deficiency inherited, and what is the risk for future children?

SP-B deficiency is inherited in an autosomal recessive pattern. This means a child must inherit two copies of the mutated SFTPB gene (one from each parent) to develop the condition. If both parents are carriers (each having one normal and one mutated gene

What are the typical symptoms of SP-B deficiency in a newborn, and when do they usually appear?

SP-B deficiency typically presents shortly after birth with severe respiratory distress. Newborns may show rapid, labored breathing, grunting, nasal flaring, and a bluish tint to the skin (cyanosis) due to low oxygen levels. These symptoms are usually evident within the first hours or days of life.

SFTPB Gene: Surfactant Protein B

The SFTPB gene provides instructions for making surfactant protein-B (SP-B), a critical component that lowers surface tension in the lungs to facilitate easy breathing and prevent alveolar collapse.

Overview and Normal Function

The SFTPB gene is located on chromosome 2. It encodes a protein known as surfactant protein-B (SP-B), which is one of four proteins found in surfactant. Surfactant is a mixture of specific fats (phospholipids) and proteins that lines the lung tissue. Its primary function is to lower surface tension, the force that causes the tissue surrounding the air sacs in the lungs (the alveoli) to stick together after exhalation.

Without normal surfactant, the alveoli collapse, making it difficult to fill the lungs with air and impairing the delivery of oxygen to the body. SP-B aids in this process by helping to spread surfactant across the surface of the lung tissue, thereby enhancing its ability to lower surface tension.

Role in Lamellar Body Formation

The phospholipids and proteins that constitute surfactant are packaged in cellular structures called lamellar bodies, which are found in specialized lung cells. Surfactant proteins undergo several processing steps to mature and become functional, with some of these steps occurring within the lamellar bodies. SP-B plays a role in the formation of these lamellar bodies, which in turn affects the processing of another surfactant protein called surfactant protein-C (SP-C).

Health Conditions Related to Genetic Changes

Surfactant Dysfunction

More than 30 mutations in the SFTPB gene have been identified that cause surfactant dysfunction, often referred to as SP-B deficiency. This condition causes severe, often fatal breathing problems in newborns.

These mutations lead to a partial or complete loss of mature SP-B, resulting in:

Abnormal composition and decreased function of surfactant.
Impaired formation of lamellar bodies.
Abnormal processing of SP-C, leading to a reduction in mature SP-C and a buildup of unprocessed forms.

The loss of functional surfactant raises surface tension in the alveoli, causing difficulty breathing and lung collapse. The combination of SP-B and SP-C dysfunction may explain why the signs and symptoms of SP-B deficiency are so severe.

Other Names for This Gene

18 kDa pulmonary-surfactant protein
6 kDa protein
PSP-B
PSPB_HUMAN
pulmonary surfactant-associated protein B
pulmonary surfactant-associated proteolipid SPL(Phe)
SFTP3
SMDP1
SP-B

Additional Information & Resources

Further information regarding the SFTPB gene can be found in the following databases and registries:

Genetic Testing Registry
PubMed (Scientific Articles)
OMIM (Catalog of Genes and Diseases)
NCBI Gene
ClinVar