Introduction to CMAMMA

Receiving a diagnosis with a name as complex as Combined Malonic and Methylmalonic Acidemia (CMAMMA) can be overwhelming. Because it shares part of its name with “classic” Methylmalonic Acidemia (MMA), it is often mistaken for that more severe condition ^[1]. However, CMAMMA is a distinct and much less severe metabolic disorder ^[2].

Understanding CMAMMA

CMAMMA is an inborn error of metabolism, meaning it is a genetic condition that changes how the body breaks down certain substances ^[3]. Specifically, people with CMAMMA have mutations in the ACSF3 gene ^[4]. This gene provides instructions for making an enzyme that helps process two specific acids: malonic acid and methylmalonic acid ^[3]. When this enzyme doesn’t work correctly, these acids build up in the blood and urine ^[4].

Is CMAMMA the Same as Classic MMA?

No. It is vital to distinguish CMAMMA from “classic” MMA. While they sound similar, their risks and daily management are very different:

• No Metabolic Crises: Classic MMA is known for causing life-threatening metabolic crises (sudden, severe illness triggered by infection or diet) ^[1]. CMAMMA does not typically cause these dangerous episodes ^[5].
• Different Chemical Signatures: Doctors tell them apart by looking at the ratio of malonic acid to methylmalonic acid in the plasma ^[6]. In CMAMMA, both are elevated, whereas in classic MMA, methylmalonic acid is usually the primary concern ^[6][4].
• Management: Classic MMA often requires highly restrictive diets or even organ transplants ^[1][5]. CMAMMA is frequently managed with much less intensive monitoring or may require no specific treatment at all ^[2].

The Controversy of “Benign” vs. “Symptomatic”

Medical experts are currently debating how to classify CMAMMA. For a long time, it was considered a benign condition—meaning it was thought to cause no symptoms or health problems ^[2].

However, more recent research has shown a wide range of experiences:

• Asymptomatic: Many people are diagnosed incidentally (by accident) through newborn screening or genetic testing and never experience a single health problem related to it ^[2][7].
• Symptomatic: Some individuals with the same ACSF3 mutations have reported neurological or psychiatric symptoms ^[3]. These can include developmental delays (slower reaching of childhood milestones), seizures (epilepsy), or psychiatric issues like memory problems or anxiety in adults ^[4][8][9].

Because of this “heterogeneity” (the wide variety of how it looks from person to person), doctors are still learning why some people feel fine while others may have symptoms ^[1][4].

How Common is CMAMMA?

CMAMMA is considered a rare disorder, but its exact incidence (how often it occurs) is unknown ^[10]. Because many people have no symptoms, it is likely underdiagnosed ^[2]. It is often only discovered when a person undergoes broad genetic testing for other reasons or in regions that use specific types of newborn urine screening ^[2][6]. Standard newborn blood screenings often miss CMAMMA because they are not looking for malonic acid ^[6][2].