Clinical, neuroradiological, and molecular characterization of patients with atypical Zellweger spectrum disorder caused by PEX16 mutations: a case series

Peroxisome biogenesis disorders—Zellweger spectrum disorders (PBD-ZSD)—are primarily autosomal recessive disorders caused by mutations in any of 13 PEX genes involved in peroxisome assembly. Compared to other PEX-related disorders, some PEX16 defects are associated with an atypical phenotype consisting of spasticity, cerebellar dysfunction, preserved cognition, and prolonged survival. In this case series, medical records and brain MRIs from 7 patients with this PEX16 presentation were reviewed to further characterize this phenotype. Classic PBD features such as sensory deficits and amelogenesis imperfecta were absent in all 7 patients, while all patients had hypertonia. Five patients were noted to have dystonia and received a treatment trial of levodopa/carbidopa. Four treated patients had partial but significant improvements in their dystonia and tremors, and 1 patient had only minimal response. Brain MRI studies commonly showed T2/FLAIR hyperintensities in the brainstem, superior and middle cerebellar peduncles, corticospinal tracts, and splenium of the corpus callosum. Genetic analysis revealed novel biallelic variants in 3 probands (c.683C > T/372delG; c.692A > G homozygous; c.865C > G/451C > T) and 1 novel variant (c.956_958delCGC) in another proband. We demonstrated residual PEX16 protein amounts by immunoblotting in fibroblasts available from 5 patients with this atypical PEX16 disease (3 from this series, 2 previously reported), in contrast to the absence of PEX16 protein in fibroblasts from a patient with the severe ZSD presentation. This study further characterizes the phenotype of PEX16 defects by highlighting novel and distinctive clinical, neuroradiological, and molecular features of the disease and proposes a potential treatment for the dystonia. ClinicalTrials.gov Identifier: NCT01668186. Date of registration: January 2012.