ABSTRACT

Objectives

Methylmalonic acidemia (MMA) is the most common inherited type of organic acidemia. It has a diverse presentation in older infants without any initial apparent symptoms. MMA sometimes presents with sudden metabolic decompensation, which may mimic common emergencies like diabetic ketoacidosis (DKA); without early recognition, it can be fatal. In this case, we aimed to emphasize that less common diagnoses such as organic acidemia should be kept in mind in infants with severe acidosis and metabolic decompensation, or in patients with an atypical clinical course to prevent serious morbidities and even death.

Materials and Methods

We report a case of MMA in an infant who presented acutely mimicking DKA and underwent long-term surveillance.

Results

An 8.5-month-old girl, the first child of an unrelated family, was admitted with complaints of vomiting and hyperglycemia and metabolic acidosis were detected. In her history, complementary feeding started at 7 months, and she had one hospital admission at 7 months due to vomiting, which improved with intravenous fluid therapy. A diagnosis of DKA was made, and appropriate fluid therapy and insulin infusion were started. However, despite achieving normoglycemia, the anion gap (AG) remained high, and metabolic acidosis persisted. Due to ongoing drowsiness and high serum ammonia levels (215 μg/dL), a metabolic disorder was suspected, and peritoneal dialysis was initiated. Tandem mass spectrometry analysis showed markedly elevated C3 propionylcarnitine levels and increased C3/C2 and C3/free carnitine ratios, while urinary organic acid analysis revealed a significant increase in methylmalonic acid excretion, along with a marked rise in 3-hydroxypropionate and methylcitrate. MUT gene analysis revealed a homozygous mutation c.360_361insT (p.K121*), confirming the diagnosis of MMA. Long-term follow-up has shown a progressive decline in her estimated glomerular filtration rate (eGFR), with even lower levels observed during acidosis attacks.

Conclusion

Inborn errors of metabolism, especially organic acidemia, should be suspected in any infant presenting with severe high AG metabolic acidosis. MMA is also associated with chronic tubulointerstitial nephritis and a progressive decline in GFR.