1X-linked disorders Biology 1F25for Biology Non-MajorsLecture 19Background Reading•Textbook, Chapter 20, especially 436-438.The People Who Prepared This LectureHarry PeeryAlan CastleX-Linked Dominant Disorders•X-Linked disorders are on the X-chromosome.•X-linked recessive disorders are common.•X-Linked dominant disorders are rare. •Vitamin-D resistant rickets is only one we will cover.
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2Rickets•Term is thought to be from Greek and refers to “a spinal complaint”•Patients with rickets have pain in their backbone due to breaking and bending of the vertebrae that make up their backbone. Rickets – due to Vitamin D deficiency or lack of calcium•In North America rickets is found in adultsdue to lack of vitamin D and calcium. In adults it can be called adult rickets or osteomalacia.•Most people who have the worst cases are dark skinned and work where they are not exposed to sun (you can work underground in Toronto and never go outside as the subway and underground walkways take you to your condominium or apartment).•Further, most adults are lactose intolerant so they cannot drink milk or milk products.Synthesis of calcitriol•UV light acts on modified cholesterol to produce vitamin D3•This goes to the liver where an OH is placed on the last carbon.•It then goes to the kidney where, in the presence of PTH, a second OH is placed on the first carbon.•This is now called calcitriol.calcitriolIllustration from Dr. Bowen, Colorado State University, Fort Collins, ColoradoVitamin-D resistant rickets•Normally, rickets is treated with Vitamin D in the diet.•However, if the enzyme that puts the final OH in the kidney is missing or defective, no amount of vitamin D will cure rickets.calcitriolIllustration from Dr. Bowen, Colorado State University, Fort Collins, ColoradoX