What you carry at this position in your DNA and what research says about it.
MCAD Deficiency Risk: 7/10 evidence, 8 publications.
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Sample genotype (not yours): A/A
Typical Fatty Acid Metabolism
Two copies of the normal gene ensure fully functional enzyme activity. This allows the body to efficiently convert medium-chain fats into energy during fasting.
What this genotype means: Normal fatty acid breakdown; Typical energy production during fasting.
Sample genotype (not yours): A/G
Healthy Carrier of MCAD Deficiency
Carrying one copy of the variant does not cause health problems because the remaining normal copy produces enough enzyme. However, there is a fifty percent chance of passing this variant to offspring.
What this genotype means: Fifty percent chance of passing variant to offspring; Typically normal metabolic function.
Sample genotype (not yours): G/G
High Risk of MCAD Deficiency
Two copies of the variant lead to a severe shortage of the enzyme needed to break down medium-chain fats. This can cause dangerous drops in blood sugar during periods of fasting or illness.
What this genotype means: Inability to metabolize medium-chain fats; Risk of severe hypoglycemia during fasting; Elevated medium-chain acylcarnitines.
Gene function and biological role
Gene Function: ACADM encodes the medium-chain acyl-CoA dehydrogenase enzyme, which is essential for breaking down medium-chain fatty acids into energy [1]. This process is especially critical during periods of fasting or illness when the body relies heavily on fat reserves [1]. Insufficient enzyme activity prevents the liver and muscles from obtaining necessary energy, leading to a buildup of toxic fatty acid byproducts [1]. The gene is highly active in mitochondria, the energy-producing centers of cells [2].
Variant Impact: Replacing lysine with glutamate at position 329 of the enzyme disrupts its structural stability and catalytic activity [2]. This specific missense change, often designated as c.985A>G or K329E, represents the most common mutation underlying medium-chain acyl-CoA dehydrogenase deficiency in populations of Northern European descent [3]. The altered protein fails to fold correctly, leading to rapid degradation within the mitochondria [2]. Consequently, metabolic processes cannot effectively break down medium-chain fats when two copies of this variant are present [3].
Key Insight: Even though MCAD deficiency is a severe metabolic condition, carriers of a single copy of the variant are typically completely asymptomatic and healthy.
Location: ACADM. Chromosome 1 · 1p31.1 · 75.8 Mb
Estimated prevalence by population
Global 99.3%; European 98.8%; African 99.8%; East Asian 100.0%; South Asian > 99.9%; Americas 99.5%; Ashkenazi 99.8%; Finnish 99.8%; Middle Eastern 100.0%; Amish 100.0%.
Estimated AA genotype frequency.
Global 0.7%; European 1.2%; African 0.2%; East Asian 0.0%; South Asian < 0.1%; Americas 0.5%; Ashkenazi 0.2%; Finnish 0.2%; Middle Eastern 0.0%; Amish 0.0%.
Estimated AG genotype frequency.
Global < 0.1%; European < 0.1%; African < 0.1%; East Asian 0.0%; South Asian < 0.1%; Americas < 0.1%; Ashkenazi < 0.1%; Finnish < 0.1%; Middle Eastern 0.0%; Amish 0.0%.
Estimated GG genotype frequency.
Showing effects for A/A genotype
Rare Genetic Disorders
Inherited Metabolic Disorders
MCAD Deficiency. Evidence: 7/10. Source: PMID 20301597. Typical Risk.
Nutrition & Metabolism
Macronutrient Metabolism
Fatty Acid Levels. Evidence: 6/10. Source: PMID 37253714. Typical.
Blood Chemistry & Metabolites
Nonanoylcarnitine Levels. Evidence: 6/10. Source: PMID 37253714. Typical.
Carnitine Levels. Evidence: 8/10. Source: PMID 33414548. Typical.
Showing effects for A/G genotype
MCAD Deficiency. Evidence: 7/10. Source: PMID 20301597. Carrier.
Fatty Acid Levels. Evidence: 6/10. Source: PMID 37253714. Slightly Elevated.
Nonanoylcarnitine Levels. Evidence: 6/10. Source: PMID 37253714. Slightly Elevated.
Carnitine Levels. Evidence: 8/10. Source: PMID 33414548. Slightly Higher.
Showing effects for G/G genotype
MCAD Deficiency. Evidence: 7/10. Source: PMID 20301597. Deficiency Risk.
Fatty Acid Levels. Evidence: 6/10. Source: PMID 37253714. Elevated.
Nonanoylcarnitine Levels. Evidence: 6/10. Source: PMID 37253714. Elevated.
Carnitine Levels. Evidence: 8/10. Source: PMID 33414548. Higher.
What this genotype means for the people who carry it
Sample genotype: AA (Homozygous)
Normal mitochondrial enzyme function is maintained by this genotype, ensuring medium-chain acyl-CoA dehydrogenase operates at full capacity [1]. This enzyme plays a vital role in breaking down medium-chain fatty acids, which are critical energy sources during periods of fasting, exercise, or illness [1]. Standard enzyme activity prevents the accumulation of potentially toxic fatty acid intermediates in tissues [2]. Consequently, there is no elevated risk of metabolic crises or associated complications like hypoglycemia [1]. The baseline metabolic state is preserved, representing the status of the vast majority of the global population [2].
Normal fatty acid breakdown; Typical energy production during fasting.
Sample genotype: AG (Heterozygous)
Inheriting one copy of the G allele makes an individual a genetic carrier for medium-chain acyl-CoA dehydrogenase (MCAD) deficiency [1]. Because this condition is inherited in an autosomal recessive pattern, carriers typically have sufficient enzyme activity to avoid any clinical symptoms [1]. Metabolic processes, including the breakdown of medium-chain fats during fasting, remain fully functional under normal conditions [2]. However, there is a 50% chance of passing this variant to children, which is important for family planning if a partner is also a carrier [1]. Screening programs often identify carriers to help families understand their reproductive risks [2].
Fifty percent chance of passing variant to offspring; Typically normal metabolic function.
Sample genotype: GG (Homozygous)
Presence of two copies of the G allele results in medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, a serious metabolic disorder [1]. Without functional enzyme activity, the body cannot convert medium-chain fatty acids into energy, particularly when fasting or experiencing metabolic stress [1]. This leads to a dangerous accumulation of medium-chain fatty acids and intermediate metabolites like nonanoylcarnitine [2]. Symptoms typically appear in infancy or early childhood and include severe hypoglycemia, lethargy, vomiting, and seizures [1]. Management focuses on avoiding fasting and ensuring rapid medical attention during illnesses to prevent metabolic crises [1]. Newborn screening programs routinely test for this variant to allow for early dietary management and prevent severe complications [2].
Inability to metabolize medium-chain fats; Risk of severe hypoglycemia during fasting; Elevated medium-chain acylcarnitines.
Variants with shared genetic architecture
rs1799958 · ACADS Gene · Chr 12 · Fatty Acid Metabolism
rs199475575 · PAH Gene · Chr 12 · Phenylketonuria Risk
rs104893688 · BTD Gene · Chr 3 · Biotinidase Deficiency
Medium-Chain Acyl-Coenzyme A Dehydrogenase Deficiency.
Whole-Genome Sequencing Analysis of Human Metabolome in Multi-Ethnic Populations.
Content updated August 2026.
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