What you carry at this position in your DNA and what research says about it.
Biotinidase Deficiency Risk: 8/10 evidence, 4 publications.
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Sample genotype (not yours): G/G
Normal Biotinidase Activity
Two copies of the normal gene result in fully functional biotinidase enzyme levels. The body efficiently recycles and utilizes biotin (vitamin B7) from the diet.
What this genotype means: Normal biotinidase enzyme activity; Efficient recycling of vitamin B7; No genetic risk for biotinidase deficiency.
Sample genotype (not yours): C/C
Mildly Reduced Biotinidase Activity
Two copies of the D444H variant result in about 48% of normal biotinidase activity. This is associated with partial biotinidase deficiency, which is usually harmless and easily managed.
What this genotype means: Biotinidase activity reduced to ~48%; Associated with partial biotinidase deficiency; Usually asymptomatic but manageable with biotin if needed.
Sample genotype (not yours): G/C
Healthy Biotinidase Deficiency Carrier
One copy of the D444H variant slightly reduces overall biotinidase enzyme activity. This represents a healthy carrier status that is highly unlikely to cause any symptoms.
What this genotype means: Slightly reduced biotinidase activity (~74%); Asymptomatic carrier status; Can pass the variant to offspring.
Gene function and biological role
Gene Function: The BTD gene provides instructions for making the enzyme biotinidase, which plays a critical role in recycling biotin, also known as vitamin B7 [1]. Biotin is an essential cofactor for several carboxylase enzymes involved in the metabolism of proteins, fats, and carbohydrates [1]. Without adequate biotinidase activity, the body cannot properly reuse biotin from dietary sources or cellular breakdown [2]. This can lead to a systemic shortage of free biotin, impairing multiple metabolic pathways [2]. Severe lack of this enzyme causes profound biotinidase deficiency, a serious but highly treatable metabolic disorder [3].
Variant Impact: The rs13078881 variant, commonly known as D444H or p.Asp424His, is a missense mutation in the BTD gene that alters a single amino acid in the biotinidase enzyme [1]. This specific structural change reduces the enzyme's activity to approximately 48% of its normal level [1]. While this reduction is mild on its own, inheriting this variant alongside a more severe BTD mutation on the other chromosome can lead to partial biotinidase deficiency [1]. It is one of the most common variants identified during newborn screening for metabolic disorders [3]. Fortunately, any associated biotin recycling issues are easily managed with simple dietary biotin supplementation [2].
Key Insight: The D444H variant retains about 48% of normal enzyme activity, making it a much milder mutation than those causing profound deficiency. Most individuals with partial deficiency remain completely healthy and asymptomatic unless experiencing severe physiological stress.
Location: BTD. Chromosome 3 · 3p25.1 · 15.6 Mb
Estimated prevalence by population
Global 94.2%; European 92.1%; African 98.4%; East Asian > 99.9%; South Asian 92.6%; Americas 94.3%; Ashkenazi 94.1%; Finnish 89.2%; Middle Eastern 92.0%; Amish 100.0%.
Estimated GG genotype frequency.
Global 5.6%; European 7.7%; African 1.6%; East Asian < 0.1%; South Asian 7.3%; Americas 5.6%; Ashkenazi 5.8%; Finnish 10.4%; Middle Eastern 7.8%; Amish 0.0%.
Estimated GC genotype frequency.
Global 0.1%; European 0.2%; African < 0.1%; East Asian < 0.1%; South Asian 0.1%; Americas 0.1%; Ashkenazi 0.1%; Finnish 0.3%; Middle Eastern 0.2%; Amish 0.0%.
Estimated CC genotype frequency.
Showing effects for G/G genotype
Rare Genetic Disorders
Inherited Metabolic Disorders
Biotinidase Activity. Evidence: 8/10. Source: PMID 34648354. Normal Activity.
Nutrition & Metabolism
Vitamin & Mineral Metabolism
Nutrient Deficiency Risk. Evidence: 3/10. Source: PMID 9654207. Typical Risk.
Biotin Recycling. Evidence: 3/10. Source: PMID 9654207. Efficient.
Showing effects for C/C genotype
Biotinidase Activity. Evidence: 8/10. Source: PMID 34648354. ~48% Activity.
Nutrient Deficiency Risk. Evidence: 3/10. Source: PMID 9654207. Partial Deficiency.
Biotin Recycling. Evidence: 3/10. Source: PMID 9654207. Reduced Efficiency.
Showing effects for G/C genotype
Biotinidase Activity. Evidence: 8/10. Source: PMID 34648354. Slightly Reduced.
Nutrient Deficiency Risk. Evidence: 3/10. Source: PMID 9654207. Carrier.
Biotin Recycling. Evidence: 3/10. Source: PMID 9654207. Typical.
What this genotype means for the people who carry it
Sample genotype: GG (Homozygous)
Two copies of the standard, fully functional BTD gene are present in this profile. The body produces biotinidase enzymes with 100% normal activity, ensuring efficient recycling of biotin [1]. Biotin is a vital B-vitamin required for the proper breakdown of fats, proteins, and carbohydrates [1]. Because this biotin recycling system works perfectly, there is no risk for biotinidase deficiency or related metabolic issues [2]. Therapeutic biotin supplements are not necessary, as standard dietary intake is completely sufficient [3]. This genotype is the most common globally, representing the baseline for healthy metabolic function.
Normal biotinidase enzyme activity; Efficient recycling of vitamin B7; No genetic risk for biotinidase deficiency.
Sample genotype: CC (Homozygous)
Two copies of the D444H variant are present in this profile, which reduces overall biotinidase enzyme activity to approximately 48% of normal levels [1]. This state is clinically classified as a form of partial biotinidase deficiency [1]. Despite the reduced enzyme activity, most people with this genetic profile remain completely healthy and never develop symptoms [2]. Symptoms, if they ever occur, are typically mild and only triggered by severe metabolic stress, such as a prolonged infection [1]. If any issues do arise, they are easily and fully preventable with simple, inexpensive oral biotin supplements [3]. Many adults with significantly reduced biotinidase activity live completely normal, symptom-free lives without ever knowing they have it [2].
Biotinidase activity reduced to ~48%; Associated with partial biotinidase deficiency; Usually asymptomatic but manageable with biotin if needed.
Sample genotype: GC (Heterozygous)
One copy of the D444H mutation in the BTD gene is present in this profile [1]. This single copy reduces the enzyme activity of that specific allele to about 48%, leaving overall biotinidase activity at roughly 70% to 80% of normal [1]. This level of enzyme function is entirely sufficient for normal health, meaning carriers do not experience symptoms of biotinidase deficiency [2]. There is, however, a small chance of passing this variant to offspring [2]. If a partner also carries a BTD mutation, future children could inherit partial biotinidase deficiency [2]. No special dietary changes or biotin supplements are necessary for personal health [3].
Slightly reduced biotinidase activity (~74%); Asymptomatic carrier status; Can pass the variant to offspring.
Variants with shared genetic architecture
rs104893687 · BTD Gene · Chr 3 · Biotinidase Deficiency
rs104893688 · BTD Gene · Chr 3 · Biotinidase Deficiency
rs119103232 · BTD Gene · Chr 3 · Biotinidase Deficiency
Partial biotinidase deficiency is usually due to the D444H mutation in the biotinidase gene.
Profound biotinidase deficiency in two asymptomatic adults.
Content updated August 2026.
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