Clinical and Genetic Spectrum of Patients With Mitochondrial Disease in a Pediatric Egyptian Cohort: Novel Variants and Phenotypic Expansion.

Mitochondrial disorders exhibit clinical and genetic diversity. Nearly 400 distinct genes, located in both the mitochondrial and nuclear genomes, harbor pathogenic variants that can produce a broad spectrum of mitochondrial diseases. This work aims to explore the genetic etiology of a cohort of Egyptian pediatric patients who were clinically suspected of having a mitochondrial disorder. A total of 49 patients from 44 unrelated families were studied. Selection criteria included age below 18 years and meeting Morava criteria (a score ≥ 3). The mitochondrial disease criteria (MDC) have been developed to quantify the clinical picture and evaluate the probability of an underlying mitochondrial disorder Exome sequencing, including mitochondrial genome sequencing, was carried out for each participant. Causative variants likely responsible for the phenotypes were identified in 68% of the study population. The mitochondrial subgroup constituted 41% of the studied population with a median age of 4 years. No primary pathogenic variants in mitochondrial DNA were detected. Pathogenic or likely pathogenic variants in eight mitochondrial genes were identified in 78% of the mitochondrial cohort. Additionally, seven novel variants were identified. Nonmitochondrial diagnoses accounted for 27% of the study population. In 32% of cases, disease-causing variants were not identified. The current study underscores the diverse phenotypic and genetic landscape of mitochondrial disorders among Egyptian patients.