Biotinidase deficiency is a genetic condition affecting the body’s ability to properly utilize the vitamin biotin. This disorder impairs the recycling of biotin, a B vitamin necessary for numerous bodily functions. Early understanding and management are important for maintaining health and preventing complications.
The Role of Biotin and Biotinidase
Biotin is a water-soluble B vitamin that plays a direct role in various metabolic processes. It functions as a coenzyme for four specific carboxylase enzymes: 3-methylcrotonyl-CoA carboxylase, pyruvate carboxylase, acetyl-CoA carboxylase, and propionyl-CoA carboxylase. These enzymes break down fats, proteins, and carbohydrates into usable energy. Biotinidase is an enzyme responsible for recycling biotin, making it available for reuse by these carboxylase enzymes.
When the biotinidase enzyme is deficient due to genetic mutations in the BTD gene, the body cannot effectively recycle biotin. This leads to a shortage of free biotin, impairing the activity of biotin-dependent carboxylases. The inability to break down fats, proteins, and carbohydrates efficiently results in a buildup of potentially toxic compounds that can damage cells and tissues. Biotinidase deficiency has two main types based on enzyme activity: profound deficiency (less than 10% of normal activity) and partial deficiency (10% to 30% of normal activity).
Recognizing the Signs
Symptoms of untreated biotinidase deficiency often become apparent within the first few months of life, though they can emerge later in childhood. Individuals with profound biotinidase deficiency may experience a range of symptoms. These can include seizures, weak muscle tone, and difficulties with breathing. Vision and hearing loss are also possible, along with problems affecting movement and balance.
Skin rashes and hair loss are common skin issues. Some affected children may also develop candidiasis. While profound deficiency presents with more severe symptoms, individuals with partial biotinidase deficiency might have milder or no symptoms, with problems appearing primarily during periods of stress such as illness or infection.
Identifying and Managing the Condition
Early diagnosis of biotinidase deficiency is important, primarily achieved through routine newborn screening tests. Most states include this condition in their newborn screening panels, which involve a simple blood test from a baby’s heel shortly after birth. If screening indicates a potential deficiency, confirmatory testing measures biotinidase enzyme activity in the blood to determine severity.
Lifelong treatment for biotinidase deficiency involves daily oral biotin supplements. This treatment should begin as soon as the diagnosis is confirmed. Consistent and timely administration of biotin can prevent the development of symptoms or significantly improve them if they have already appeared. With proper treatment, individuals with biotinidase deficiency can often lead healthy lives with normal growth and development, although some complications like vision or hearing loss, if already present, may not be fully reversible.
How Biotinidase Deficiency is Inherited
Biotinidase deficiency is an inherited disorder. It follows an autosomal recessive pattern of inheritance, meaning a child must inherit two copies of a mutated BTD gene—one from each parent—to be affected.
Parents who carry one mutated BTD gene copy are usually asymptomatic, as they also possess one working copy. When both parents are carriers, there is a 25% chance with each pregnancy that their child will inherit two mutated copies and develop biotinidase deficiency. There is also a 50% chance their child will be a carrier, and a 25% chance their child will inherit two normal copies of the gene.