From OMIM
SPR deficiency results in neurologic deterioration due to severe dopamine and serotonin deficiencies in the central nervous system caused by a defect in BH4 synthesis. Clinically, affected individuals show an L-DOPA-responsive, diurnally fluctuating movement disorder usually associated with cognitive delay and severe neurologic dysfunction. BH4 is a required cofactor for the synthesis of the neurotransmitters dopamine and serotonin. BH4 is also a required cofactor for phenylalanine hydroxylase (PAH; 612349), but patients with SPR deficiency do not exhibit overt hyperphenylalaninemia. The lack of hyperphenylalaninemia distinguishes SPR deficiency from other disorders of BH4 synthesis (see, e.g., HPABH4A, 261640). However, the neurologic phenotype of SPR deficiency resembles the other BH4-deficient disorders (summary by Bonafe et al., 2001 and Friedman et al., 2012). Another form of dopa-responsive dystonia (DTY5; 128230) is caused by mutation in the gene encoding GTP cyclohydrolase I (GCH1; 600225), which is also a component of the biopterin synthetic pathway.  http://www.omim.org/entry/612716

From MedlinePlus Genetics
Sepiapterin reductase deficiency is a condition characterized by movement problems, most often a pattern of involuntary, sustained muscle contractions known as dystonia. Other movement problems can include muscle stiffness (spasticity), tremors, problems with coordination and balance (ataxia), and involuntary jerking movements (chorea). People with sepiapterin reductase deficiency can experience episodes called oculogyric crises. These episodes involve abnormal rotation of the eyeballs; extreme irritability and agitation; and pain, muscle spasms, and uncontrolled movements, especially of the head and neck. Movement abnormalities are often worse late in the day. Most affected individuals have delayed development of motor skills such as sitting and crawling, and they typically are not able to walk unassisted. The problems with movement tend to worsen over time.

People with sepiapterin reductase deficiency may have additional signs and symptoms including an unusually small head size (microcephaly), intellectual disability, seizures, excessive sleeping, and mood swings.  https://medlineplus.gov/genetics/condition/sepiapterin-reductase-deficiency

From MedlinePlus Genetics
Dopa-responsive dystonia is a disorder that involves involuntary muscle contractions, tremors, and other uncontrolled movements (dystonia). The features of this condition range from mild to severe. This form of dystonia is called dopa-responsive dystonia because the signs and symptoms typically improve with sustained use of a medication known as L-Dopa.

Signs and symptoms of dopa-responsive dystonia usually appear during childhood, most commonly around age 6. The first signs of the condition are typically the development of inward- and upward-turning feet (clubfeet) and dystonia in the lower limbs. The dystonia spreads to the upper limbs over time; beginning in adolescence, the whole body is typically involved. Affected individuals may have unusual limb positioning and a lack of coordination when walking or running. Some people with this condition have sleep problems or episodes of depression more frequently than would normally be expected.

Over time, affected individuals often develop a group of movement abnormalities called parkinsonism. These abnormalities include unusually slow movement (bradykinesia), muscle rigidity, tremors, and an inability to hold the body upright and balanced (postural instability).

The movement difficulties associated with dopa-responsive dystonia usually worsen with age but stabilize around age 30. A characteristic feature of dopa-responsive dystonia is worsening of movement problems later in the day and an improvement of symptoms in the morning, after sleep (diurnal fluctuation).

Rarely, the movement problems associated with dopa-responsive dystonia do not appear until adulthood. In these adult-onset cases, parkinsonism usually develops before dystonia, and movement problems are slow to worsen and do not show diurnal fluctuations.  https://medlineplus.gov/genetics/condition/dopa-responsive-dystonia