In both cases, supplementation with biotin can often restore normal metabolic function and proper catabolism of leucine and isoleucine.The symptoms of biotinidase deficiency (and dietary deficiency of biotin) can be quite severe. A 2004 case study from Metametrix detailed the effects of biotin deficiency, including aggression, cognitive delay, and reduced immune function. Genetics
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) are metabolized differently.Individuals lacking functional biotinidase enzymes can still have normal carboxylase activity if they ingest adequate amounts of biotin. The standard treatment regimen calls for 5–10 mg of biotin per day.Biotinidase deficiency is inherited in an autosomal recessive pattern, which means the defective gene is located on an autosome, and two copies of the defective gene - one from each parent - must be inherited for a person to be affected by the disorder.
"Newborn screening for biotinidase deficiency in Brazil: biochemical and molecular characterizations". Brazilian Journal of Medical and Biological Research. 37 (3): 295–9. doi:10.1590/S0100-879X2004000300001. PMID 15060693. Weber, Peter; Scholl, Sabine; Baumgartner, E Regula (2007). "Outcome in patients with profound biotinidase deficiency: relevance of newborn screening". Developmental Medicine & Child Neurology. 46 (7): 481–4. doi:10.1111/j.1469-8749.2004.tb00509.x. PMID 15230462. Wolf, Barry (2003). "Biotinidase deficiency: New directions and practical concerns". Current Treatment Options in Neurology. 5 (4): 321–8. doi:10.1007/s11940-003-0038-4. PMID 12791199. S2CID 25158348. External links
OMIM entries on Biotinidasa deficiency

 This article incorporates public domain material from Genetics Home Reference. United States National Library of Medicine.