Several forms of autosomal recessive parkinsonism are known. In three forms, 
caused by mutations in parkin (PARK2), PINK1 (PARK6), or DJ-1 (PARK7), the 
phenotype is usually characterized by levodopa-responsive parkinsonism without 
atypical features. Parkin mutations are most frequent, explaining -50% of the 
cases with a clinical diagnosis of familial Parkinson's disease compatible with 
recessive inheritance and onset <45 years, and -15% of the sporadic cases with 
onset <45. Mutations in PINK1 and DJ-1 are less common, accounting for -1-8%, 
and -1-2% of the sporadic cases with early-onset. Since point mutations and 
genomic rearrangements can be present, sequencing and exon dosage are both 
required for accurate mutational screening of these genes. The phenotype of 
parkin mutations is characterized by early-onset parkinsonism, good response to 
levodopa, and benign course. The average onset age is in the 30s, but late-onset 
cases have been described. The phenotype associated with PINK1 and DJ-1 
mutations has been studied in a smaller number of patients but it is overall 
indistinguishable from that of parkin. Mutations in other genes, including 
ATP13A2 (PARK9), PLA2G6 (PARK14), and FBX07 (PARK15), cause more rare forms of 
recessive parkinsonism with very early-onset (<30 years) and usually additional, 
atypical features (pyramidal, dystonic, ocular movement, and cognitive 
disturbances). Yet, it is expected that other monogenic forms of parkinsonism 
will be identified in the future, as mutations in the above-mentioned genes are 
not found in other patients with similar phenotypes.