Vitamin D-dependent rickets

Vitamin D-dependent rickets is a group of disorders that are characterized by soft, weak bones (rickets). In people with these conditions, the process by which minerals are deposited into developing bones (mineralization) is disrupted. The long bones in the arms and legs are particularly affected. People with vitamin D-dependent rickets have problems using vitamin D, which helps maintain the proper levels of calcium and phosphate in the blood. These minerals are needed for the normal development of strong bones and teeth.

There are several forms of vitamin D-dependent rickets: type 1A (VDDR1A), type 1B (VDDR1B), type 2A (VDDR2A), type 2B (VDDR2B), and type 3 (VDDR3). The types are distinguished by their genetic cause.

The signs and symptoms of vitamin D-dependent rickets often begin in infancy. Infants with vitamin D-dependent rickets may have weak muscle tone (hypotonia) and fail to grow or gain weight at the expected rate (failure to thrive). When affected children begin to walk, they may develop abnormally curved (bowed) legs because the bones are too weak to bear weight. The weakened bones are often painful and are prone to fractures. Bone growth is often delayed, and affected individuals may be shorter than their peers. Additional skeletal features include enlargement of the skull, the wrists, and the ends of the ribs.

Affected individuals may also have dental abnormalities, such as delayed tooth formation and thin tooth enamel. Some people with vitamin D-dependent rickets who have very low levels of calcium in the blood can have muscle cramps, tingling sensations (paresthesias), or seizures. Hair loss (alopecia) has been reported in some individuals with VDDR2A.

With early treatment, affected individuals may have less-severe skeletal signs and symptoms and fewer long-term health issues. Unlike with some other forms of rickets, vitamin D-dependent rickets cannot be treated with standard doses of vitamin D.