Among these, 13 genes encode proteins of the electron transport chain (abbreviated "ETC"), 22 encode transfer RNA (tRNA), and two encode the large and small subunits that form ribosomal RNA (rRNA). The 13 proteins involved in the ETC of the mitochondrion are necessary for oxidative phosphorylation. Mutations in these proteins results in impaired energy production by mitochondria. This cellular energy deficit manifests most readily in tissues that rely heavily upon aerobic metabolism such as the brain, skeletal and cardiac muscles, sensory organs, and kidneys. This is one factor involved in the presentation of mitochondrial diseases.There are other factors involved in the manifestation of a mitochondrial disease besides the size and location of a mutation. Mitochondria replicate during each cell division during gestation and throughout life. Because the mutation in mitochondrial disease most often occurs early in gestation in these diseases, only those mitochondria in the mutated lineage are defective. This results in an uneven distribution of dysfunctional mitochondria within each cell, and among different tissues of the body. This describes the term heteroplasmic which is characteristic of mitochondrial diseases including KSS. The distribution of mutated mtDNA in each cell, tissue, and organ, is dependent on when and where the mutation occurs. This may explain why two patients with an identical mutation in mtDNA can present with entirely different phenotypes and in turn different syndromes. A publication in 1992 by Fischel-Ghodsian et al. identified the same 4,977-bp deletion in mtDNA in two patients presenting with two entirely different diseases.
A prolonged treatment course is indicated, with patients usually requiring at least 4-6 months of treatment. Patients who are treated with larger doses of steroids require prophylaxis against pneumocystis jirovecii. Relapses may occur and are more likely to occur in severe disease or when steroids are tapered too soon or too quickly. Alternative or adjunct treatment options include macrolide antibiotics (due to anti-inflammatory properties), azathioprine and cyclophosphamide. References
External links

"Idiopathic Interstitial Pneumonias". Merck Manual Professional. May 2008.