A homozygous frameshift mutation of sepiapterin reductase gene causing parkinsonism with onset in childhood.

We report two siblings that presented hypotonia and very early-onset parkinsonism. Homozygosity mapping using SNP genome scan data identified a candidate locus that was 12.2 Mega base pairs. By exome sequencing, we found a homozygous five-nucleotide deletion (c.448_452delAGAAC) in gene Sepiapterin Reductase (SPR). The mutation is predicted to lead to premature translational termination. Sepiapterin reductase deficiency (SRD) is a recently recognized dopa-responsive dystonia. Our findings show that SRD can manifest as early-onset parkinsonism, widening the spectrum of the disease phenotype and adding to the genetic heterogeneity of the disease.