Nitrous oxide is a chemically inert, faintly sweet-smelling gas known colloquially as "laughing gas," "nangs," "whippets," or "balloons" [1].Inhaled, it has a pleasant, empathogenic effect that dissipates within minutes. It has been used or misused for >2 centuries [2]. Because it is now not only cheap and legal but also easily bought in bulk online, its recreational misuse has become a public health issue worldwide,

Acute intermittent porphyria is a rare genetic condition in which disrupted haem synthesis causes overproduction of porphyrin precursors. Occasionally, it is associated with posterior reversible encephalopathy syndrome (PRES), presenting with headache, confusion, seizures and visual disturbance. We describe a patient with acute intermittent porphyria who presented with seizures and PRES, and who had previous unexplained severe abdominal pain. Acute intermittent porphyria should be considered as a possible cause of PRES, especially in those with unexplained abdominal pain, since delays in its diagnosis can result in permanent complications.

Background: Leber hereditary optic neuropathy (LHON) is one of the more common mitochondrial diseases and is rarely associated with mitochondrial renal disease. We report 3 unrelated patients with a background of adult-onset renal failure who presented to us with LHON and were shown to have a heteroplasmic mitochondrial DNA mutation (m.13513G>A). Methods: Retrospective chart review. Results: All 3 patients had a background of chronic renal failure and presented to us with bilateral optic neuropathy (sequential in 2) and were found to have heteroplasmic m.13513G>A mutations in the MT-ND5 gene. Two of the patients were females (aged 30 and 45 years) with chronic kidney disease from their 20s, attributed to pre-eclampsia, one of whom also had diabetes and sudden bilateral hearing loss. One patient was a male (aged 54 years) with chronic kidney disease from his 20s attributed to IgA nephropathy. His mother had diabetes and apparently sudden bilateral blindness in her 70s. Renal biopsy findings were variable and included interstitial fibrosis, acute tubular necrosis, focal segmental glomerulosclerosis, and IgA/C3 tubular casts on immunofluorescence. Mild improvements in vision followed treatment with either idebenone or a combination supplement including coenzyme Q10, alpha-lipoic acid, and B vitamins. Conclusions: Our cases expand the clinical syndromes associated with m.13513G>A to include bilateral optic neuropathy and adult-onset renal disease. This highlights that in patients with bilateral, especially sequential, optic neuropathy a broad approach to mitochondrial testing is more useful than a limited LHON panel. Mitochondrial diseases present a diagnostic challenge because of their clinical and genetic variability.