Early-onset parkinsonism-intellectual disability syndrome
Early-onset parkinsonism-intellectual disability syndrome is a very rare genetic disorder which is characterized by intellectual disabilities, psychomotor developmental delays, macrocephaly, and Parkinson's disease which starts before the age of 45 (early onset PD). Additional symptoms include epilepsy, strabismus, and frontal bossing. Causes 

This disorder is either caused by alterations or deletions of the RAB39B gene in chromosome Xq28 which are inherited in an X-linked recessive manner. Epidemiology 

More than 12 cases from 3 families from Australia and the U.S. have been described in medical literature. References 

X-linked recessive disorders
Genetic syndromes
Syndromes with intellectual disability
Parkinson's disease
Neurodegenerative disorders