Early-Onset Parkinsonism and Halo Sign: Beta-propeller Protein-associated Neurodegeneration

A 13-year-old girl with infantile-onset self-resolving epilepsy and developmental delay had an unremarkable workup, including normal brain magnetic resonance imaging (MRI) and chromosomal microarray. During adolescence, she presented with features of early-onset parkinsonism: gait dyspraxia, freezing during walking, cogwheel rigidity in both upper extremities, and left arm dystonia. Repeat brain MRI showed iron deposition on the substantia nigra (SN) and basal ganglia, with hyperintense halo sign around a central linear hypointensity within the SN on the T1 imaging sequence. Whole-exome sequencing with trio revealed de novo heterozygote mutation in WDR45 to confirm the diagnosis of beta-propeller protein-associated neurodegeneration (BPAN). BPAN is a rare neurodegenerative with brain iron accumulation disorder with the pathognomonic halo sign. Preferential iron deposition over the SN compared to globus pallidus can distinguish this condition from other iron storage disorders. BPAN does not cause the radiologic eye of the tiger sign seen in other forms of iron storage disorders. Other types of childhood-onset parkinsonian disorders, such as PINK1-related Parkinson disease and Parkin-type Parkinson disease, do not have iron storage in the brain. This report describes a case of early-onset parkinsonism secondary to a mutation in WDR45. It underscores the importance of brain MRI to differentiate this condition from other childhood-onset parkinsonism and also other brain iron accumulation disorders. This report also shows iron deposition over the pituitary as a novel site of iron deposition in BPAN and emphasizes the presence of peri-dentate white matter volume loss and hyperintensity, which is another key radiologic abnormality associated with BPAN.