<prompt> Tiger eye appearance on MRI brain is characteristic feature of:Refsums diseaseHallervorden Spatz diseaseNARP mitochondrial diseaseAbetalipoproteinemia  <response>: Ans. B. Hallervorden Spatz diseaseHallervorden- Spatz Disease are neurodegenerative disorder of basal gangliaDefinitionHallervorden- Spatz disease HSD is a rare disorder characterized by progressive extrapyramidal dysfunction and dementia. Its an iron metabolic disorder.Genetics1. The disease can be familial or sporadic. When familial, it is inherited recessively and has been linked to chromosome 20.2. Recently, a mutation in the pantothenate kinase PANK2 gene on band 20pl3 has been described in patients with typical HSD.Clinical features: -1. Onset is most commonly in late childhood or early adolescence.2. progressive extrapyramidal dysfunction and dementia.3. Visual impairment from optic atrophy or retinal degeneration is not uncommon and can be the presenting symptom of the disease, although this is rare.MRIbilaterally symmetric hyperintense signal changes in anterior medial globus pallidus with surrounding hypointensity in the globus pallidus on T2-weighted images Eye-of-the-tiger sign. 