Achondrogenesis type 1B

A rare genetic disorder affecting bone and cartilage development

Achondrogenesis type 1B is a rare genetic disorder characterized by severe skeletal dysplasia, which affects the development of bones and cartilage. It is one of the subtypes of achondrogenesis, a group of disorders that result in short stature and other skeletal abnormalities. Achondrogenesis type 1B is inherited in an autosomal recessive pattern.

Genetics

Achondrogenesis type 1B is caused by mutations in the SLC26A2 gene, which provides instructions for making a protein involved in the development of cartilage and bone. This gene is located on chromosome 5. The mutations lead to a deficiency in the protein's function, resulting in the characteristic skeletal abnormalities of the disorder.

Pathophysiology

The SLC26A2 protein is essential for the normal development of cartilage, which is a precursor to bone. In achondrogenesis type 1B, the defective protein disrupts the normal process of endochondral ossification, where cartilage is gradually replaced by bone. This disruption leads to the accumulation of cartilage and underdeveloped bones, particularly affecting the spine, ribs, and limbs.

Clinical Features

Individuals with achondrogenesis type 1B typically present with:

• Severe short stature
• Shortened limbs (micromelia)
• Narrow chest with short ribs
• Underdeveloped lungs
• Hydrops fetalis (severe swelling in the fetus)
• Polyhydramnios (excess amniotic fluid)

These features are usually evident on prenatal ultrasound and can lead to complications during pregnancy and delivery.

Diagnosis

Diagnosis of achondrogenesis type 1B is based on clinical features, radiographic findings, and genetic testing. Prenatal ultrasound may reveal characteristic skeletal abnormalities. Genetic testing can confirm mutations in the SLC26A2 gene.

Management

There is currently no cure for achondrogenesis type 1B. Management focuses on supportive care and addressing complications. Due to the severity of the condition, many affected infants are stillborn or die shortly after birth. Genetic counseling is recommended for affected families.

Related pages

• Achondrogenesis
• Skeletal dysplasia
• Autosomal recessive inheritance
• SLC26A2

Gallery

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  Diagram of autosomal recessive inheritance

Achondrogenesis type 1B

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  Diagram showing autosomal recessive inheritance pattern