Lecture 19 - X-linked Disorders

Lecture 19 - X-linked Disorders - Lecture 19 Background...

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1 X-linked disorders Biology 1F25 for Biology Non-Majors Lecture 19 Background Reading Textbook, Chapter 20, especially 436- 438. The People Who Prepared This Lecture Harry Peery Alan Castle X-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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2 Rickets • 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 adults due 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. calcitriol Illustration from Dr. Bowen, Colorado State University, Fort Collins, Colorado Vitamin-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. calcitriol Illustration from Dr. Bowen, Colorado State University, Fort Collins, Colorado X
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3 Treatment of vitamin-D resistant rickets • Because the enzyme in the kidneys is missing, no amount of vitamin D in the diet will be converted to calcitriol. • No amount of calcium in the diet will help either because it cannot be absorbed without calcitriol. • The only treatment is to give calcitriol itself. X-Linked Recessive Disorders I: A Clinical Case Lecture 19 X-Linked Recessive • 25% of children will be affected. • 25% of children will be carriers. • 50% will be normal. A Case of Infertility • Female patient whom we will call “Sandra” (this is not her real name) • Age: 32 • Married 5 years • Hears her biological clock ticking and wants to have at least 2 children. • Has tried getting pregnant but no success
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4 The Physical Exam • Appearance: normal well-developed female habitus (appearance). • Pelvic exam: normal (all internal and external
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This note was uploaded on 06/10/2008 for the course BIOL BIOL-1F25 taught by Professor Peery during the Spring '08 term at Brock University, Canada.

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Lecture 19 - X-linked Disorders - Lecture 19 Background...

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