Symptoms and the Highly Variable Phenotype

One of the most challenging aspects of Combined Malonic and Methylmalonic Acidemia (CMAMMA) is its unpredictability. In the medical world, this is called a variable phenotype—meaning that even though two people have the same genetic mutation, their health experiences can be completely different ^[1][2].

The Asymptomatic Experience

For many individuals, CMAMMA is a “silent” condition. It is frequently discovered by accident through newborn screening or carrier screening (genetic tests done before having children) ^[2][3].

• A “Benign” Course: Many children and adults with CMAMMA never develop any symptoms at all ^[2].
• Normal Growth: In these cases, growth, intelligence, and physical development usually proceed exactly as expected ^[4].

Symptoms in Childhood

When symptoms do appear in children, they primarily affect the nervous system. Because CMAMMA involves mitochondrial energy, the brain—which uses a huge amount of energy—is often the first place to show signs of stress ^[5].

• Developmental Differences: Some children may take longer to reach milestones like walking or talking. In some symptomatic cases, traits associated with autism or intellectual disability have also been reported ^[6][7].
• Seizures and Epilepsy: A significant symptom for some is refractory epilepsy (seizures that are difficult to control with standard medication) ^[6]. This can sometimes take the form of Lennox-Gastaut syndrome, a severe type of epilepsy involving multiple seizure types ^[6].

Symptoms in Adulthood

In some cases, CMAMMA does not cause issues until later in life. These symptoms are often “insidious,” meaning they come on slowly over time ^[7].

• Cognitive and Memory Changes: Adults may notice a gradual cognitive decline or problems with memory that seem unusual for their age ^[7][8].
• Psychiatric Symptoms: Some adults have experienced significant psychiatric disturbances, such as increased aggression, anxiety, or other unexplained changes in behavior ^[7].

Why the Difference?

It remains a mystery why some people with ACSF3 deficiency have severe symptoms while others have none. Researchers believe it may be due to:

• Secondary Triggers: A severe illness, extreme stress, or certain environmental factors might “trigger” symptoms in someone who was previously asymptomatic ^[4].
• Dual Diagnosis: Sometimes, a person with CMAMMA also has a mutation in a different gene that makes their symptoms look more severe ^[9].

Because of this range, it is important to treat the person, not just the lab results. If a person is feeling well and meeting milestones, many doctors consider the condition benign ^[2]. If symptoms are present, a specialized metabolic team can help create a management plan ^[9].