While it was initially regarded as a recessive (or purely homozygous) disorder, some researchers have reported the existence of similarly deleterious effects from the heterozygous form of the SNP.

[2] In the homozygous form of the mutation, a single genetic base (character) has been changed from cytosine ("C") to thymine ("T") on both strands of Chromosome 1 – in other words, "C;C" has been replaced by "T;T".

[3] For reasons that are not understood, many people with defective variants of the AMPD genes are asymptomatic, while others have symptoms including exercise intolerance, and/or muscle pain and cramping.

[1] There is an increased risk that statin (cholesterol-reducing drugs) will cause myopathy (muscle weakness) in individuals with MADD.

[10] Anesthesia has the potential to cause malignant hyperthermia, an uncontrolled increase in body temperature, and permanent muscle damage in patients with MADD.

Instead of being converted to IMP, the AMP builds up in the cells of affected individuals, spills into the blood, and is eventually metabolized in the liver[citation needed].

In persons with a defective enzyme, 5'-nucleotidase removes the ribose and phosphorus from AMP, increasing levels of adenosine measured in muscle cells by ~16–25×, after exercise.

Once the cell has received a non-trivial load, and has expended the phosphocreatine reserve, a small quantity of ATP will become discharged down to AMP.

The pool of AMP also grows bigger than in the controls, which would cause higher rate of glucose liberation from glycogen.

This may lead to onset of acute thirst some tens of minutes into exercise in this state, if the water balance in the body was neutral initially.

In case of leg muscles, where circulation is substantially dependent on their cyclical contraction when the body is upright, a small but useful degree of initial up-regulation of the citric acid cycle may be achieved just by standing still for a few minutes.

There is little or no warning for nearing toxicity, because the purine nucleotide energy charge is still relatively high, the leg muscles do not cramp, and remain functional.

On the other hand, in persons with balanced AMPD and myophosphorylase activities in muscle cells, lactic acid and ammonia are produced simultaneously, counteracting each other's effects to some degree.

Some seldom used but strong voluntary muscles, such as those involved in "pushing" during the act of defecation, are not tuned for aerobic mode, and may dump plenty of purines during their short work routine, if it happens in this state.

If a food containing even small but perceivable amount of sugar (simple sugars or disaccharides that can be tasted sweet, or starch that is at least minimally hydrolyzed by salivary amylase, or even some non-sugar sweeteners) is eaten in this state, there may be a period of time after it enters stomach and before bulk absorption occurs, when continuous exercise becomes very hard, and easily triggers rhabdomyolysis.

It probably happens because the digestive system senses and signals forthcoming delivery of sugars, inhibiting fatty acid release and oxidation, and starving glycogen-less muscle cells of the sole available source of energy.

If the person is at rest at this moment, and pays attention, a sudden increase in the breathing frequency due to lactate dumping is readily observable.

If the rise in the blood lactate is particularly sharp, and the person happened to be breathing slowly, a heart palpitation may sometimes be observable.

Delayed stomach emptying creates especially favorable conditions for the shock lactic acidosis, because the digestive system may meanwhile still inhibit fatty acid release and oxidation, helping more muscles to run out of glycogen in those persons, who are otherwise still able to maintain its stores between meals.

Once all AMP has been recharged to ATP, and glycogen stores allowed to replenish, the cell transitions back to the unmodified original state.

It may be especially important to have adequate dietary iodine in the glycogen-less state, so that stomach emptying is not excessively delayed, the up-regulation of the citric acid cycle in muscle cells in response to a load increment is not too slow, and the muscles can each time accept a bigger load increment relative to the perceived effort.

[citation needed] It is important for MADD patients to maintain strength and fitness without exercising or working to exhaustion.

[19] Symptomatic relief from the effects of MADD may sometimes be achieved by administering ribose orally at a dose of approximately 10 grams per 100 pounds (0.2 g/kg) of body weight per day, and exercise modulation as appropriate.

Patients with myoadenylate deaminase deficiency do not retain ribose during heavy exercise, so supplementation may be required to rebuild levels of ATP.