Guest guest Posted May 20, 2003 Report Share Posted May 20, 2003 A while back I asked Paolo (Dr. Vinci) to explain type X and also I asked about X dominant and X recessive. What follows is what he helped me understand. ~ Gretchen --------------------------------------------------------- CMT X (written by Dr. Vinci) X-linked inheritance is special. Females have two X and males only have one; so any pathological gene on chromosome X causes the disease in males. Despite that females have two X, only one cell each is allowed to work. According to the hypothesis of Lyon,* in the early stages of the embrional development in a cell population, one X is randomly suppressed and all the cells that will originate from that cell will have the same X suppressed. The situation is similar in males. But females are less severely affected because in the females some cells originate from the cells whose good X was suppressed and some from those whose bad X was suppressed. So the females are mosaic: if the cells with a good X are more numerous than the ones with the bad X, the disease will be mild or absent. In theory they should be 50/50. At this point it is important to know if the gene is dominant or recessive. In the females it should cause the disease only if dominant; for example, if that gene produces a pathological protein that alters the good protein produced by the good gene. This mechanism is called " dominant-negative " . CMT X due to a pathological connexin 32 is dominant; that's why females also have the disease, but more often mild. There are also 2 forms of CMT X that are recessive. * Lyon's hypothesis Also known as Lyon's phenomenon Associated persons: Frances Lyon Description: Hypothesis stating that only one of the two X-chromosomes is genetically active in female cells. X inactivation occurs around the 16th day of embryonic development. Bibliography: M. F. Lyon: Gene action in the X-chromosome of the mouse (Mus musculus). Nature, London, 1961, 190: 372-373. Theory of differential inactivation of the X-chromosome. Quote Link to comment Share on other sites More sharing options...
Guest guest Posted September 3, 2003 Report Share Posted September 3, 2003 <liliwigg@...> wrote: > Were you ever tested for Type X? ~ Gretchen No Gretchen, I don't think there is a need with male to male transmission. In example, My grandad passed it to my dad and he in turn passed it to me. Also my grandad's brother passed it to one of his sons, (a daughter too but that doesn't count here). I probably didn't make that very clear in my post. Jim in Ohio Quote Link to comment Share on other sites More sharing options...
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