Clinical heterogeneity of LRRK2 p.I2012T mutation

- The phenotypes of LRRK2 p.I2012T mutation include PD and FTD with parkinsonism.
- There is lack of correlation between phenotype and genotype in LRRK2-parkinsonism.
- NGS is a powerful diagnostic tool for families with neurodegenerative disorders.

IntroductionLeucine-rich repeat kinase 2 (LRRK2) mutations are the most common genetic cause of Parkinson's disease (PD). However, only few cases carrying LRRK2 mutations have been reported in Taiwanese PD patients.MethodsWe used targeted next generation sequencing (NGS), covering 24 candidate genes involved in neurodegenerative disorders, to analyze 40 probands with familial PD, and 10 patients with mixed neurodegenerative disorders. Sanger sequencing of the identified mutation in the first set of the study was performed in additional 270 PD patients, including 139 familial PD and 131 early-onset PD (onset age less than 50 years old), and 300 age/gender matched control subjects.ResultsWe found a missense variant, p.I2012T, in the LRRK2 gene in one sporadic patient having early-onset frontotemporal dementia with parkinsonism and dystonia. Sanger sequencing this substitution in additional 270 PD patients in the second set of the study revealed two additional variant carriers: one having autosomal-dominant familial PD, and one with sporadic PD. The p.I2012T substitution was absent in 300 normal control subjects. Analyzing family members of the proband with p.I2012T revealed co-segregation of the variant and parkinsonism. Clinical presentations, levodopa responses, and Tc99mTRODAT-SPECT imaging findings of this index family were similar to idiopathic PD.ConclusionsOur results revealed clinical heterogeneity of the LRRK2 p.I2012T substitution, and demonstrated the use of targeted NGS for genetic diagnosis in multiplex families with PD or mixed neurodegenerative disorders.