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Case Study
Joey is a seven-year-old boy with developmental delay and chronic constipation. His parents have recently noted that he cannot keep up with other children at the neighborhood playground, becoming exhausted after 30 minutes of play. On multiple occasions, Joey has had limited use of his legs after exercise, complains of leg pain, and must be carried home by his parents. He recovers from these episodes after a period of rest. Joey's concerned parents bring him to your primary care office for evaluation.
Etiology
Historically known as the "powerhouse" of the cell, the mitochondria play a key role in maintaining energy home- ostasis for all tissues in the body (McFarland & Turnbull, 2010). In 1959, R. Luft evaluated a woman with severe per- spiration, generalized weakness, and an inability to gain weight; a muscle biopsy determined her symptoms were caused by a disorder of her mitochondria (Luft, 1994). Nearly 30 years later, the first mutation of mitochondrial DNA (mtDNA) was identified in an individual with optic neuropathy, giving rise to the understanding that changes in mtDNA alter energy production, in this case, causing ophthalmic disease (Wallace et al., 1988). Since then, the understanding of mitochondrial energy production, mtDNA mutation, and clinical effects on individuals, has exponentially grown. Alterations in mtDNA causing decreased cellular energy production are now understood to cause more than 400 different syndromes. These disor- ders are collectively known as mitochondrial disease (Jeyakumar, Williamson, Brickman, Krakovitz, & Parikh, 2009).
The primary purpose of mitochondria is to produce adenosine triphosphate (ATP) (Kisler, Whittaker, & McFarland, 2010). Mitochondria convert the caloric supply of macronutrients (carbohydrates, amino acids, fatty acids) to ATP by oxidative phosphorylation (OXPHOS) through a series of reactions, producing essential energy required by all tissues in the human body (Schiff et al., 2011). In mito- chondrial disease, one or more of these reactions do not function properly, causing a disruption in cellular energy production. Often, parents or guardians of a child with mitochrondrial disease will use a "car analogy" to describe their child's condition. It is as if their child is a six-cylinder car running on only two cylinders; as long as they are driv- ing on a flat country road, they do fine. But as soon as they start going up...