Malonic acid to methylmalonic acid ratio
The use of plasma rather than urine is recommended for determining the ratio of malonic acid to methylmalonic acid. Since even with an increase in sensitivity for malonic acid (MA), concentrations in urine samples can be so subtle that they are easily missed. In contrast, if only urinary methylmalonic acid (MAA) is used as the sole matrix, then CMAMMA due to ACSF3 may be misdiagnosed as classic methylmalonic acidemia. Also the calculation of the MA/MAA ratio in urine is not useful, because due to overlapping, healthy individuals cannot be clearly distinguished from CMAMMA affected individuals. Whereas, by calculating the MA/MMA ratio in plasma, a CMAMMA can be clearly distinguished from a classic methylmalonic acidemia. This is true for both, vitamin B12 responders and non-responders in methylmalonic acidemia.In CMAMMA due to ACSF3, methylamlonic acid levels exceed those of malonic acid. In contrast, in CMAMMA due to malonyl-CoA deficiency, the MMA/MA ratio is less than 1. Genetic testing
Extended carrier screening (ECS) in the course of fertility treatment can also identify carriers of mutations in the ACSF3 gene. Treatments
Dietary
One approach to reduce the accumulating amount of malonic acid and methylmalonic acid is diet. Here, a diet high in carbohydrate and low in protein has been shown to be best. Changes in malonic acid and methylmalonic acid excretion can be seen as early as 24-36 h after a change in diet. Bacteria-reducing measures
Another quantitatively significant source of malonic acid and methylmalonic acid, in addition to dietary protein intake, is bacterial fermentation.
To likely compensate for the cells energy demand, an upregulation of fatty acid β-oxidation and a decreased concentration of certain amino acids that feed anaplerotically into the citrate cycle, such as glutamine (via the fifth site of the citrate cycle), leucine, isoleucine, threonine (all via the sixth site of the citrate cycle) and aspartate (via the 10th site of the citrate cycle), could be detected. In summary, this reduced mitochondrial respiration and glycolytic flux results in impaired mitochondrial flexibility with a large dependence on fatty acid β-oxidation.However, neurons, with the exception of hypothalamic neurons, are not capable of satisfying their large energy demands by degrading fatty acids. It is speculated that an upregulation of β-oxidation also occurs in brain cells due to the hypofunctional mtFASII pathway. The consequence would be an increased risk for hypoxia and oxidative stress, which may contribute to neurological symptoms in the long term. Methylmalonic acid
Methylmalonic acid is formed from the essential amino acids valine, methionine, threonine and isoleucine, from odd-chained fatty acids, from propionate and from cholesterol side chain, on the degradation path into the citrate cycle. In this process, the last intermediate methylmalony-CoA can be converted to methymalonic acid by a deacylase before incorporation at the succinyl-CoA site of the citrate cycle. At this point, the acyl-CoA synthease encoded by ACSF3 could convert the methylmalonic acid back to methylmalonyl-CoA and then feed it to the citrate cycle with the help of the methylmalonyl-CoA mutase and its cofactor vitamin B12.