A case of drug-induced parkinsonism and tardive akathisia with e1143g polymerase γ mutation-innocent bystander or a culprit?

BACKGROUND AND AIM

Polymerase γ (POLG) is a protein that plays a pivotal role in the replication of the mitochondrial genome. POLG-related disorders constitute a sequence of overlying phenotypes that can present from early infancy to late adulthood. Parkinsonism is the most common movement disorder associated with POLG mutation. We also summarize all reported cases of POLG-related Parkinsonism, along with a literature review.

CASE DESCRIPTION

We present the case of an 80-year-old male presented with complaints of episodic confusion, tremors, and restlessness. He has been on risperidone for psychosis. A normal DaT scan ruled out Parkinson's disease, and molecular analysis for POLG was positive (E1143G). He was diagnosed with drug-induced Parkinsonism and tardive akathisia with an incidental POLG mutation.

CONCLUSIONS

A literature search revealed 55 cases of "POLG-related Parkinsonism" that met our criteria. These mutations can clinically affect multiple organ systems. Parkinsonism is the most common movement disorder reported in association with POLG mutations. We conducted a molecular analysis in our patient due to his Parkinsonism and recurrent episodes of encephalopathy. E1143G mutation found in our case was coincidental and reported a non-pathogenic or benign variant in literature.

RELEVANCE FOR PATIENTS

E1143G is a non-pathogenic variant and multiple studies have shown that its co-occurrence with other POLG mutations can aggravate disease occurrence and severity. Literature findings and the experience from our own case indicate that the pathogenicity of E1143G is debatable, and future studies involving this particular variant may help understand its pathological consequences.