Adenosine monophosphate deaminase deficiency type 1

Lore & Background

The disorder is caused by a defect in the mechanism for producing AMP deaminase, an enzyme that converts adenosine monophosphate (AMP) to inosine monophosphate (IMP). In virtually all cases, the deficiency has been caused by an SNP mutation known as rs17602729 or C34T, where a single base change from cytosine to thymine occurs on both strands of Chromosome 1. A rarer analogous condition involving a change from guanine to adenine has also been identified. While initially regarded as a recessive disorder, some researchers have reported similarly deleterious effects from the heterozygous form, though no consensus exists on its effects.

Symptoms include exercise intolerance, muscle pain, cramping, and fatigue. The deficiency lowers aerobic power output, requiring increased anaerobic power for the same work. Excess adenosine released during heavy activity can cause fatigue and sedation, and muscle pain is partially due to high lactate levels. Recovery from over-exertion can range from hours to months, especially in cases of rhabdomyolysis. Muscle weakness is not a major symptom initially, but chronic muscle damage from rhabdomyolysis can eventually cause significant weakness.

Reader's Guide

AMPD1 deficiency is significant as a model of how a single enzyme defect can disrupt energy metabolism, particularly in muscle. The disorder affects approximately 1–2% of people of predominantly European descent but is considerably rarer in Asian populations. Its study has highlighted the role of the purine nucleotide cycle in ATP regeneration during exercise. The condition also illustrates genetic complexity: while homozygous mutations are clearly pathogenic, the effects of heterozygous forms remain debated. Clinically, the deficiency increases risks from statin-induced myopathy and anesthesia-related malignant hyperthermia. Many individuals are asymptomatic, suggesting modifying factors or compensatory mechanisms. The disorder's legacy includes informing understanding of exercise physiology, adenosine signaling, and the interplay between genetic variation and metabolic disease.

Did You Know?

• The deficiency was formerly known as myoadenylate deaminase deficiency (MADD).
• In the homozygous form of the common mutation, cytosine (C;C) is replaced by thymine (T;T) on both strands of Chromosome 1.
• Some evidence suggests that the heterozygous form (C;T or A;G) may also cause AMPD1 deficiency, though no consensus exists.
• There is an increased risk that statin drugs will cause myopathy in individuals with MADD.