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A biotinidase Km variant causing late onset bilateral optic neuropathy
V T Ramaekers1, T M Suormala, M Brab
1Department of Paediatrics and Ophthalmology, Technical University of Aachen, Germany.
Archives of Disease in Childhood
|January 1, 1992
Summary
A rare biotinidase deficiency variant caused vision loss and neurological issues in a child. Prompt biotin treatment reversed symptoms, highlighting the importance of diagnosing this treatable condition.
Area of Science:
- Biochemistry
- Genetics
- Neurology
Background:
- Biotinidase deficiency is an inborn error of metabolism affecting biotin recycling.
- A novel variant of biotinidase deficiency presented with severe neurological and visual impairment.
Observation:
- A 10-year-old patient developed acute vision loss, progressing to bilateral optic neuropathy, spastic paraparesis, and motor neuropathy.
- Metabolic investigations confirmed biotin depletion and multiple carboxylase deficiency due to a mutant biotinidase with residual activity.
- Plasma biotinidase exhibited biphasic kinetics, indicating a complex enzymatic defect.
Findings:
- The patient's condition improved significantly after six months of oral biotin supplementation.
- Neurological deficits, including optic neuropathy and pyramidal signs, regressed, and motor neuropathy progression halted.
- Asymptomatic patients with partial biotinidase deficiency and normal Michaelis constant (Km) for biocytin were identified for comparison.
Implications:
- Biotinidase deficiency should be considered in the differential diagnosis of juvenile-onset optic neuropathy with motor neuron disease.
- Early diagnosis and biotin treatment can prevent or reverse severe neurological complications.
- Understanding the enzyme kinetics of mutant biotinidase is crucial for predicting disease severity.