Biotinidase Deficiency

Definition

Definition of Biotinidase Deficiency
Biotinidase deficiency is an inherited disorder in which the body is unable to reuse and recycle the vitamin biotin. This disorder is classified as a multiple carboxylase deficiency, a group of disorders characterized by impaired activity of certain enzymes that depend on biotin.

Symptoms

Symptoms of Biotinidase Deficiency
The signs and symptoms of biotinidase deficiency typically appear within the first few months of life, but the age of onset varies. Children with profound biotinidase deficiency, the more severe form of the condition, often have seizures, weak muscle tone (hypotonia), breathing problems, and delayed development. If left untreated, the disorder can lead to hearing loss, eye abnormalities and loss of vision, problems with movement and balance (ataxia), skin rashes, hair loss (alopecia), and a fungal infection called candidiasis. Immediate treatment and lifelong management with biotin supplements can prevent many of these complications.

Causes

Causes of Biotinidase Deficiency
Mutations in the BTD gene cause biotinidase deficiency. Biotinidase is the enzyme that is made by the BTD gene. Many mutations that cause the enzyme to be nonfunctional or to be produced at extremely low levels have been identified. Biotin is a vitamin that is chemically bound to proteins. (Most vitamins are only loosely associated with proteins.) Without biotinidase activity, the vitamin biotin cannot be separated from foods and therefore cannot be used by the body. Another function of the biotinidase enzyme is to recycle biotin from enzymes that are important in metabolism (processing of substances in cells). When biotin is lacking, specific enzymes called carboxylases cannot process certain proteins, fats, or carbohydrates. Specifically, two essential branched-chain amino acids (leucine and isoleucine) cannot be completely broken down, and are instead diverted into harmful by-products such as hydroxyisovalerate (also referred to as hydroxyisovaleric acid).

Diagnosis

Diagnosis of Biotinidase Deficiency
Biotinidase deficiency can be found by genetic testing. This is often done at birth as part of newborn screening in several states throughout the United States. Results are found through testing a small amount of blood gathered through a heel prick of the infant. As not all states require that this test be done, it is often skipped in those where such testing is not required. Biotinidase deficiency can also be found by sequencing the BTD gene, particularly in those with a family history or known familial gene mutations.

Treatment

Treatment of Biotinidase Deficiency
Treatment is possible but unless continued daily, problems may arise. Currently, this is done through the taking of 5-10 mg of oral biotin a day. If symptoms have begun to show, standard treatments can take care of them, such as hearing aids for poor hearing.

Prognosis

Prognosis of Biotinidase Deficiency
Consult with your doctor.

Prevention

Prevention of Biotinidase Deficiency
Consult with your doctor.