Propionic aciduria (PA), also known as Propionic acidemia, is a rare autosomal recessive metabolic disorder that is caused by a deficiency in the enzyme propionyl-CoA carboxylase. The incidence of PA is estimated to occur in approximately 1 in 100,000 births.
Propionyl-CoA carboxylase converts propionyl-CoA to methylmalonyl-CoA, which is a reaction that helps convert certain amino acids and fats into energy. The non-functional enzyme leads to the accumulation of propionyl-CoA, which eventually results in the accumulation of acids and other toxic compounds that lead to a myriad of downstream consequences. Clinically, the typical presentation is in the neonatal period, although rarely some patients may present at an older age. The most common features in PA include: poor feeding, hypotonia, acidosis, seizures, episodic vomiting, as well as lethargy and ketosis. Less severe forms may present in older children or adults with vomiting, lethargy, failure to thrive, protein intolerance, seizures and psychomotor abnormalities. It should be noted that both hypertrophic and dilated cardiomyopathy is estimated to occur in approximately 25-50% of patients.
In general, MRI imaging findings are non-specific for propionic acidemia. In neonates, T2/FLAIR sequences show non-specific edema and signal irregularities in the cerebral white matter with sparing of the basal ganglia. DWI will show restricted diffusion in the areas affected, in both older children and neonates. In older children, T2/FLAIR sequences reveal hyperintensities in the basal ganglia, with an emphasis on the caudate and putamen, and T1 hypointensity. In there cerebral cortex and cerebellar cortex, abnormal signal intensities are less common. In the untreated form of the disease, myelination abnormalities as well as cortical white matter atrophy can be expected. Proton MR spectroscopy in PA will show decreased N-acetylaspartate and myo-I levels, and increased glutamine and glutamate in the basal ganglia.
References
1. Barkovich AJ. Pediatric Neuroimaging. Wolters Kluwer Lippincott Williams & Wilkings
2. Karimzadeh P, Jafari N, Ahmad AF et al. Propionic acidemia. Diagnosis and neuroimaging findings of this neurometabolic disorder. Iranian Journal of Child Neurology. 2014;8(1):58-61