Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Importance: Mutations in the gene encoding parkin (PARK2) are the most common cause of autosomal recessive juvenile-onset and young-onset parkinsonism. The few available detailed neuropathologic reports suggest that homozygous and compound heterozygous parkin mutations are characterized by severe substantia nigra pars compacta neuronal loss. Objective: To investigate whether parkin-linked parkinsonism is a different clinicopathologic entity to Parkinson disease (PD). Design, Setting, and Participants: We describe the clinical, genetic, and neuropathologic findings of 5 unrelated cases of parkin disease and compare them with 5 pathologically confirmed PD cases and 4 control subjects. The PD control cases and normal control subjects were matched first for age at death then disease duration (PD only) for comparison. Results: Presenting signs in the parkin disease cases were hand or leg tremor often combined with dystonia. Mean age at onset was 34 years; all cases were compound heterozygous for mutations of parkin. Freezing of gait, postural deformity, and motor fluctuations were common late features. No patients had any evidence of cognitive impairment or dementia. Neuronal counts in the substantia nigra pars compacta revealed that neuronal loss in the parkin cases was as severe as that seen in PD, but relative preservation of the dorsal tier was seen in comparison with PD (P=.04). Mild neuronal loss was identified in the locus coeruleus and dorsal motor nucleus of the vagus, but not in the nucleus basalis of Meynert, raphe nucleus, or other brain regions. Sparse Lewy bodies were identified in 2 cases (brainstem and cortex). Conclusions and Relevance: These findings support the notion that parkin disease is characterized by a more restricted morphologic abnormality than is found in PD, with predominantly ventral nigral degeneration and absent or rare Lewy bodies.705571579Reta Lila Weston Trust for Medical ResearchParkinson's UKParkinson Disease FoundationReta Lila Weston TrustFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)University of CampinasMonumental Trust Award from Parkinson's UKBayer-ScheringBiogen IdecLundbeckMedtronicIrish Institute of Clinical NeuroscienceMater CollegePRTL1Multiple System Atrophy TrustAlzheimer's Research UKPSP AssociationNational Institute for Health Research Biomedical Research Unit at University College London Hospitals, University College LondonDublin Brain BankWellcome Trust/MRC Joint Call in Neurodegeneration awardFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)