A Girl with Myelopathy and Vision Loss, Misdiagnosis as Neuromyelitis Optica Spectrum Disorder: The First Iranian Case Report on Biotinidase Deficiency

Introduction: Biotinidase (BTD) deficiency may lead to variable neurologic manifestations. Spinal cord involvement can be an unusual presentation of the late-onset disorder. Case Presentation: We describe a six-year-and-ten-month-old girl with a previous history of recurrent upper respiratory tract infections, frequent falling four years before admission, gradual vision loss, and subacute progressive limb weakness followed by flaccid quadriplegia during admission. The measurements of cerebrospinal fluid (CSF) lactate showed significant elevation. And spinal MRI revealed longitudinally extensive cord involvement, mimicking acquired demyelinating syndrome; however, there was no response to plasma exchange. Profound biotinidase deficiency was confirmed by enzyme assay; the patient revealed dramatic recovery after the biotin prescription. The genetic analysis showed ahomozygous missense variant BTD (NM_001370658.1): c.838A C (p.Asn280His) in exon 4, thereby predicting pathogenic based on the ACMG guidelines. To the best of our knowledge, this is the first Iranian report on BTD deficiency. Conclusions: In summary, in each patient with longitudinally extensive cord involvement not well responding to the conventional treatment, BTD deficiency should be considered on differential.