The parents of a child with an autosomal recessive disorder are carriers of one copy of the defective gene, but are usually not affected by the disorder. Nutritional
Though not always grouped together with the inherited versions, a severe nutritional deficiency of vitamin B12 can also result in syndrome with identical symptoms and treatments as the genetic methylmalonic acidemias. Methylmalonyl-CoA requires vitamin B12 to form succinyl-CoA. When the amount of B12 is insufficient for the conversion of cofactor methylmalonyl-CoA into succinyl-CoA, the buildup of unused methylmalonyl-CoA eventually leads to methylmalonic acidemia. This diagnosis is often used as an indicator of vitamin B12 deficiency in serum. Mechanism
Pathophysiology
In methylmalonic acidemia, the body is unable to break down the amino acids methionine, threonine, isoleucine and valine; as a result methylmalonic acid builds up in the blood and tissues. Those afflicted with this disorder are either lacking functional copies or adequate levels of one or more of the following enzymes: methylmalonyl-CoA mutase, methylmalonyl-CoA epimerase, or those involved in adenosylcobalamin synthesis. Methylmalonyl-CoA mutase
It is estimated that as many as 60% of cases are the result of a mutated MUT gene which encodes the protein methylmalonyl-CoA mutase. This enzyme is responsible for the digestion of potentially toxic derivatives of the breakdown of the above-mentioned amino acids and fats, primarily cholesterol, particularly this enzyme converts methylmalonyl-CoA into succinyl-CoA. Without this enzyme, the body has no means to neutralize or remove methylmalonic acid and related compounds.
Though currently unclear if this is due to the specific mutation or early detection and treatment, despite complete nonresponse to cobalamin supplements, these individuals appeared to develop a largely benign and near completely asymptomatic version of MMA. Despite consistently showing elevated methylmalonic acid in the blood and urine, these individuals appeared for the large part developmentally normal. Notable cases
Ryan Stallings, a St. Louis infant, was mistakenly diagnosed with ethylene glycol poisoning instead of MMA in 1989, leading to a wrongful murder conviction and life sentence for his mother, Patricia Stallings. See also
Combined malonic and methylmalonic aciduria (CMAMMA)
Isovaleric acidemia
Propionic acidemia
Maple syrup urine disease

Notes
References
Further reading


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