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Sepiapterin reductase deficiency
Sepiapterin reductase deficiency is an inherited pediatric disorder characterized by movement problems, and most commonly displayed as a pattern of involuntary sustained muscle contractions known as dystonia. Symptoms are usually present within the first year of age, but diagnosis is delayed due to physicians lack of awareness and the specialized diagnostic procedures.〔 Individuals with this disorder also have delayed motor skills development including sitting, crawling, and need assistance when walking. Additional symptoms of this disorder include intellectual disability, excessive sleeping, mood swings, and an abnormally small head size. SR deficiency is a very rare condition. The first case was diagnosed in 2001, and since then there have been approximately 30 reported cases. At this time, the condition seems to be treatable, but due to a lack of overall awareness and a series of atypical procedures used to diagnose this condition pose a dilemma.〔Lohmann, E., Koroglu, C., Hanagasi, H. A., Dursun, B., Tasan, E., & Tolun, A. (2012). A homozygous frameshift mutation of sepiapterin reductase gene causing parkinsonism with onset in childhood. Parkinsonism & Related Disorders, 18(2), 191-193. 〕
==Causes==
This disorder occurs through a mutation in the SPR gene, which is responsible for encoding the signals that create sepiapterin reductase enzyme. The enzyme is involved in the last step of producing tetrahydrobiopterin better known as BH4. BH4 is involved in the processing of amino acids and the production of neurotransmitters, specifically that of dopamine and serotonin which are primarily used in transmission of signals between nerve cells in the brain. The mutation in the SPR gene interferes with the production of the enzyme by producing enzymes with little or no function at all. This interference results in a lack of BH4 specifically in the brain. The lack of BH4 only occurs in the brain because other parts of the body adapt and utilize alternate pathways for the production of BH4. The mutation in the SPR gene leads to nonfunctional sepiapterin reductase enzymes, which results in a lack of BH4 and ultimately disrupts the production of dopamine and serotonin in the brain.〔Clot, F., Grabli, D., Cazeneuve, C., Roze, E., Castelnau, P., Chabrol, B., . . . French Dystonia, N. (2009). Exhaustive analysis of BH4 and dopamine biosynthesis genes in patients with Dopa-responsive dystonia. Brain, 132, 1753-1763.〕 The disruption of dopamine and serotonin production leads to the visible symptoms present in patients suffering from sepiapterin reductase deficiency. SR deficiency is considered an inherited autosomal recessive condition disorder because each parent carries one copy of the mutated gene, but typically do not show any signs or symptoms of the condition.〔Pearl, P. L., Taylor, J. L., Trzcinski, S., & Sokohl, A. (2007). The pediatric neurotransmitter disorders. Journal of Child Neurology, 22(5), 606-616. doi: 10.1177/0883073807302619.〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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