Non-Frame shift Mutation of Dystrophin gene causes:
Correct Answer: Becker's Muscular Dystrophy
Description: Duchenne&;s and Becker&;s Muscular Dystrophies are both caused by a mutation on the dystrophin gene located on the X Chromosome (Xp21). An out-of-Frame mutation typically results in complete disruption of dystrophin production and causes Duchenne&;s Dystrophy. An in-Frame mutation results in a shoened but semi-functional dystrophin and causes Becker&;s Dystrophy. X-Linked recessive mutation of the dystrophin gene on the Sacrolemmal membrane Mutations are located in the Dystrophin gene on XP21 Since these are X-Linked Recessive disorders, they occur primarily in boys. (Females are usually Asymptomatic carriers with a normal gene on one X Chromosome and a mutant gene on the other X-Chromosome. Frame-shift-mutation (Out-of-Frame) - Results in complete loss of dystrophin - Duchenne muscular dystrophy Non-Frame shift mutation (In-Frame) - Results in paial function of dystrophin - Becker muscular dystrophy Clincal severity more dependent on in-frame versus out-of-frame mutation ("reading-frame-rule"), rather than the location of the mutation along the gene. Mutations disrupting the translational reading frame of the gene (Frameshift mutation) result in near total loss of dystrophin and usually lead to DMD, while in-frame mutation result in the translation of semi-functional dsytrophin of abnormal size and/or amount, typically resulting in outlier of BMD clinical phenotypes. Although there are exceptions to the "reading-frame rule", 92% of phenotypic differences are explained by in-frame and out-of-frame mutations. Ref: Robbins and cotran 9th edition Vol 2
Category:
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