Genotype-Phenotype Correlation in Progressive External Ophthalmoplegia: Insights From a Retrospective Analysis

Area of Science:

• Mitochondrial genetics
• Neuromuscular disorders
• Clinical pathology

Background:

• Progressive external ophthalmoplegia (PEO) is a hallmark of mitochondrial disease, but its genetic underpinnings and clinical correlations are not fully understood.
• Investigating the relationship between specific mitochondrial DNA (mtDNA) variations and PEO phenotypes is crucial for diagnosis and management.

Purpose of the Study:

• To analyze the clinical, pathological, and genetic characteristics of PEO patients based on their mtDNA variations.
• To correlate different types of mtDNA variations (single large-scale deletions, multiple deletions, m.3243A>G point variant) with disease severity and clinical presentation.

Main Methods:

• Eighty-two PEO patients were categorized by mtDNA variation type: single large-scale deletions (SLDs), multiple deletions (MulDs), and the m.3243A>G point variant.
• SLD patients were further classified into 'common deletion' and 'noncommon deletion' groups.
• Mutational load of deleted mtDNA was quantified using real-time PCR (RT-PCR).

Main Results:

• SLD patients exhibited a higher proportion of cytochrome C oxidase-negative (COX-n) fibers. Mutational load inversely correlated with deletion length and directly with COX-n fiber ratio.
• Compared to noncommon deletions, common deletions in SLD patients were associated with more muscle involvement, lower BMI, higher mutational load, more COX-n fibers, and elevated GDF15 levels.
• MulDs patients presented milder symptoms than the m.3243A>G variant group, with later onset, higher BMI, lower lactate, and fewer ragged-blue fibers (RBFs).

Conclusions:

• The m.3243A>G variant group displayed the most severe PEO symptoms, followed by SLD patients with common deletions.
• These findings improve understanding of PEO heterogeneity, aiding in diagnosis, prognosis, and genetic counseling for mitochondrial disorders.