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Biotinidase is an enzyme that recycles biotin, a water-soluble vitamin essential as the coenzyme for four carboxylases that are involved in gluconeogenesis, fatty acid synthesis and in the catabolism of several branched-chain amino acids. Biotinidase deficiency (BD) is an autosomal recessively inherited disorder. Individuals with profound BD (<10% of mean normal serum biotinidase activity) present usually during early childhood with neurological disorders (seizures, hypotonia, ataxia, developmental delay, vision problems and hearing loss) and/or non-neurological findings (metabolic acidosis, respiratory difficulties, alopaecia and/or skin rash), that may progress to coma or death if untreated.1 Here, we present two cases of adult-onset BD with reversible optic neuropathy (ON).
An 18-year-old man was referred with a 7-month history of bilateral progressive painless visual loss. He was born in France and his parents were from sub-Saharan Africa. There was no relevant familial medical history and no known consanguinity. On admission, decimal visual acuity (VA) of both eyes was <20/200 and ophthalmological examination showed bilateral, predominantly temporal, optic disc pallor. Goldmann perimetry demonstrated a bilateral centrocaecal scotoma. Spectral domain optical coherence tomography (Spectralis; Heidelberg Engineering, Heidelberg, Germany; SD-OCT) showed thinning of the peripapillary retinal nerve fibres layer (right eye, OD 78 µm and left eye, OS 73 µm) with preferential involvement of the temporal quadrant. Total macular volume measurements were normal. Visual evoked potential (VEP) and colour discrimination were not performed. His neurological examination was unremarkable. Brain MRI showed T2-weighted hyperintensities of both optic nerves and chiasm without Gadolinium enhancement and spinal MRI revealed bilateral longitudinally extensive high T2-signal intensities of anterior part of the spinal …
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