Nitric oxide and hypoxia

NO (nitric oxide) can affect mitochondrial function by interacting with the cytochrome c oxidase (complex IV) of the electron transport chain in a manner that is reversible and in competition with oxygen. Concentrations of NO too low to inhibit respiration can trigger cell defence response mechanisms involving reactive oxygen species and various signalling molecules such as nuclear factor kappa B and AMP kinase. Inhibition of mitochondrial respiration by NO at low oxygen concentrations can cause so-called metabolic hypoxia and divert oxygen towards other oxygen-dependent systems. Such a diversion reactivates prolyl hydroxylases and thus accounts for the prevention by NO of the stabilization of hypoxia-inducible transcription factor. In certain circumstances NO interacts with superoxide radical to form peroxynitrite, which can affect the action of key enzymes, such as mitochondrial complex I, by S-nitrosation. This chapter discusses the physiological and pathophysiological implications of the interactions of NO with the cytochrome c oxidase.

Factors influencing success of clinical genome sequencing across a broad spectrum of disorders

To assess factors influencing the success of whole-genome sequencing for mainstream clinical diagnosis, we sequenced 217 individuals from 156 independent cases or families across a broad spectrum of disorders in whom previous screening had identified no pathogenic variants. We quantified the number of candidate variants identified using different strategies for variant calling, filtering, annotation and prioritization. We found that jointly calling variants across samples, filtering against both local and external databases, deploying multiple annotation tools and using familial transmission above biological plausibility contributed to accuracy. Overall, we identified disease-causing variants in 21% of cases, with the proportion increasing to 34% (23/68) for mendelian disorders and 57% (8/14) in family trios. We also discovered 32 potentially clinically actionable variants in 18 genes unrelated to the referral disorder, although only 4 were ultimately considered reportable. Our results demonstrate the value of genome sequencing for routine clinical diagnosis but also highlight many outstanding challenges.