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D-Bifunctional protein deficiency (officially called 17-β-hydroxysteroid dehydrogenase IV deficiency) is an autosomal recessive peroxisomal fatty acid oxidation disorder. Peroxisomal disorders are usually caused by a combination of peroxisomal assembly defects or by deficiencies of specific peroxisomal enzymes. The peroxisome is an organelle in the cell similar to the lysosome that functions to detoxify the cell. Peroxisomes contain many different enzymes, such as catalase, and their main function is to neutralize free radicals and detoxify drugs, such as alcohol. For this reason peroxisomes are ubiquitous in the liver and kidney. D-BP deficiency is the most severe peroxisomal disorder, often resembling Zellweger syndrome.〔 〕 Characteristics of the disorder include neonatal hypotonia and seizures, occurring mostly within the first month of life, as well as visual and hearing impairment. Other symptoms include severe craniofacial disfiguration, psychomotor delay, and neuronal migration defects. Most onsets of the disorder begin in the gestational weeks of development and most affected individuals die within the first two years of life. ==Classification== DBP deficiency can be divided into three types: * type I, characterized by a deficiency in both the hydratase and dehydrogenase units of D-BP * type II, in which only the hydratase unit is non-functional * type III, with only a deficiency in the dehydrogenase unit Type I deficient patients showed a large structural modification to the D-BP as a whole. Most of these individuals showed either a deletion or an insertion resulting in a frameshift mutation. Type II and III patients showed small scale changes in the overall structure of D-BP(). Amino acid changes in the catalytic domains or those in contact with substrate or cofactors were the main cause of these variations of D-BP deficiency. Other amino acid changes were seen to alter the dimerization of the protein, leading to improper folding. Many mutations have been found in the gene coding for D-BP(HSD17B4)on the q arm two of chromosome five (5q2) in ''Homo sapiens'', most notably individuals homozygous for a missense mutation (616S).〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「D-bifunctional protein deficiency」の詳細全文を読む スポンサード リンク
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