Turner syndrome (Year of the Zebra) — Transcript

Full transcript

1. 0:00[Music]
2. 0:03Turner syndrome named after Henry Turner
3. 0:05who first described it is a chromosomal
4. 0:08disorder affecting females where One X
5. 0:10chromosome is either completely or
6. 0:12partially
7. 0:13absent now our DNA is this humongous
8. 0:16blueprint of information on how to make
9. 0:18a human which is usually packaged up
10. 0:21nicely into 46 chromosomes these 46
11. 0:24chromosomes come in 23 Pairs and each
12. 0:27pair has one chromosome from each parent
13. 0:30one of these pairs the sex chromosomes
14. 0:33determines a person's biological sex and
15. 0:35can be made up of either two X
16. 0:37chromosomes for females or an X and A Y
17. 0:40chromosome for
18. 0:42males so if you wanted to make another
19. 0:45human first you'd have to find someone
20. 0:47that feels the same way and then you
21. 0:49both contribute half of your chromosomes
22. 0:52in order to package up half the
23. 0:53chromosomes into either a sperm cell or
24. 0:56an egg cell you actually start with a
25. 0:58single cell that has 4 6 chromosomes
26. 1:01let's just say we're making a sperm cell
27. 1:03for Simplicity we're going to show one
28. 1:06pair of chromosomes but remember that
29. 1:08all 23 pairs do this the first step is
30. 1:11meiosis which is what produces our sex
31. 1:13cells and the chromosomes replicate and
32. 1:16so now they're sort of shaped like an X
33. 1:19even though there are two copies of DNA
34. 1:21here we still say it's one chromosome
35. 1:23since they're hooked together in the
36. 1:25middle by this thing called a
37. 1:27centromere okay then the cell splits
38. 1:29into into two and pulls apart the paired
39. 1:32chromosomes so in each of these cells
40. 1:34you've now got 23
41. 1:36chromosomes now the two copies of the
42. 1:39chromosomes get pulled apart and the
43. 1:40cells split again which means four cells
44. 1:44each still with 23
45. 1:46chromosomes now these are ready to pair
46. 1:48up with an egg cell from Mom that has 23
47. 1:51chromosomes as well totaling to 46
48. 1:54chromosomes and voila 9 months down the
49. 1:57road you've got yourself a baby
50. 2:00usually each parent contributes one
51. 2:03chromosome to each pair
52. 2:0550/50 sometimes though one parent might
53. 2:08contribute one chromosome to many and
54. 2:10this is called triom or one chromosome
55. 2:13less which is called monosomy monosomy
56. 2:16is what happens in Turner syndrome and
57. 2:18it specifically affects the X chromosome
58. 2:21there are three potential kot type
59. 2:23scenarios associated with turner
60. 2:25syndrome most commonly an entire X
61. 2:28chromosome is missing giving a 45x kot
62. 2:31type in other words the person only has
63. 2:3445 chromosomes missing one of the X
64. 2:38chromosomes this can happen as a result
65. 2:41of non-disjunction of sex chromosomes
66. 2:43during meiosis and it happens more
67. 2:45frequently in sperm cells but egg cells
68. 2:48can also be affected non-disjunction
69. 2:50means the chromosomes don't split apart
70. 2:53so following meiosis one resulting cell
71. 2:55ends up with both chromosomes and the
72. 2:58other gets none multiply by by two and
73. 3:00the final result is two cells with an
74. 3:02extra chromosome and two cells missing a
75. 3:05chromosome non-disjunction can also
76. 3:07happen in the Second Step though so
77. 3:10first step goes great and both cells
78. 3:12have a chromosome but if they don't
79. 3:14split apart in the Second Step then the
80. 3:16final result is one cell with an extra
81. 3:18chromosome one cell missing a chromosome
82. 3:21and two with the right number of
83. 3:24chromosomes now if an egg cell combines
84. 3:27with any of these sperm cells that have
85. 3:29the missing Chrome Rome then you get
86. 3:30Turner
87. 3:32syndrome the next most common scenario
88. 3:34is mosaicism meaning the individuals
89. 3:37have some cells in their body with the
90. 3:3945 xot type and others with a 46 XX
91. 3:43carot type this happens because of an
92. 3:46error following conception so conception
93. 3:50results in a single cell the zygote that
94. 3:52divides over and over again essentially
95. 3:55producing every kind of cell in the body
96. 3:58each of these divisions is called
97. 4:00mitosis non-disjunction of the sex
98. 4:02chromosomes can also happen during any
99. 4:05mitosis in which case you'd end up with
100. 4:08one cell line that has three sex
101. 4:10chromosomes so 47 in total and one cell
102. 4:13line missing an X chromosome so 45
103. 4:16chromosomes in
104. 4:18total but if the prior divisions
105. 4:20progress normally there's also one cell
106. 4:23line with 46 chromosomes that contribute
107. 4:26cells to the developing fetus now the
108. 4:28cell line with 4 47 chromosomes rarely
109. 4:31survive but the one with 45 does and
110. 4:34continues to replicate and produce more
111. 4:36cells with only 1 X chromosome along
112. 4:38with a 46 XX cell line leading to a mix
113. 4:42of 45x and 46 XX cells in the
114. 4:48body the least common kot type in Turner
115. 4:51syndrome is where there's only part of
116. 4:53the X chromosome missing basically a
117. 4:56section of the chromosome for example
118. 4:58the short arm is deleted at some point
119. 5:00during meiosis but the rest of the
120. 5:02chromosome is passed on this can also
121. 5:05happen at some point during mitosis and
122. 5:08the result is another Mosaic kot type as
123. 5:11far as we know these errors happen at
124. 5:13random so parents who have a child with
125. 5:16turner syndrome are not at a higher risk
126. 5:18than others of having a second child
127. 5:20with the same
128. 5:23condition now only having one complete X
129. 5:26chromosome impacts the female
130. 5:28reproductive system by increasing the
131. 5:30rate of loss of eggs which normally
132. 5:32happens more slowly by two years of age
133. 5:35none are left essentially causing
134. 5:37menopause before menarchy without eggs
135. 5:41the ovaries fail to develop normally
136. 5:43becoming non-functional fibrous streak
137. 5:46ovaries these streak ovaries can't
138. 5:49produce sex hormones resulting in
139. 5:51hypogonadism and low estrogen levels the
140. 5:54body will respond by producing more
141. 5:56follicle stimulating hormone or FSH and
142. 5:59lutenizing hormone or LH since these
143. 6:03hormones stimulate estrogen secretion by
144. 6:05the
145. 6:06ovaries the X chromosome also carries
146. 6:09genes that are important for growth and
147. 6:10development of tissues throughout the
148. 6:12body one of these is the short stature
149. 6:15homeobox gene or S Hawks for short so
150. 6:18having a single copy of the S Hawks Gene
151. 6:20results in you guessed it short stature
152. 6:24there are also plenty of other
153. 6:25unidentified genes on the X chromosome
154. 6:28so individuals with erer syndrome are
155. 6:30predisposed to cardiovascular defects
156. 6:33like preductal coarctation of the aorta
157. 6:35and bicuspid aortic valve they might
158. 6:38have kidney issues specifically A
159. 6:40congenital abnormality called horseshoe
160. 6:42kidney where the two kidneys become
161. 6:44fused during fetal development they
162. 6:47might also have lymphatic and skeletal
163. 6:49abnormalities and are at a higher risk
164. 6:51for type 2 diabetes and
165. 6:54hypothyroidism just how many of these
166. 6:57abnormalities linked with turner
167. 6:58syndrome are present depends on the
168. 7:01proportion of cells the person has with
169. 7:03the 45x kot
170. 7:06type signs and symptoms of Turner
171. 7:09syndrome vary depending on the age of
172. 7:10the person and on how much of the second
173. 7:12X chromosome is
174. 7:14missing infants may be born with
175. 7:16lymphadema or swelling due to a buildup
176. 7:19of lymph in their hands and feet many
177. 7:22also have lymph related swelling of the
178. 7:24back of the neck causing a cystic
179. 7:26hygroma which eventually decreases as
180. 7:28they age this often leaves extra skin on
181. 7:31the neck called neck webbing which gives
182. 7:33the appearance of having a wider than
183. 7:35normal neck coarctation of the aorta and
184. 7:38a bicuspid aortic valve can cause lower
185. 7:42extremity cyanosis meaning a bluish or
186. 7:44purplish discoloration of the lower
187. 7:46Limbs and can result in congestive heart
188. 7:49failure children with horseshoe kidney
189. 7:52are more likely to have urinary tract
190. 7:55infections in adolescence skeletal
191. 7:58abnormalities become
192. 7:59like short stature and a broad chest
193. 8:02with widely spaced nipples low set ears
194. 8:05and arms that turn outward at the elbows
195. 8:07also called cubitus valgus because it
196. 8:10causes streak ovaries Turner syndrome is
197. 8:12also the most common cause of primary
198. 8:14Amara which is when a female hasn't
199. 8:17begun breast development by age 13 or
200. 8:20hasn't had menarchy by age 15 as a
201. 8:23result many females with turner syndrome
202. 8:25are
203. 8:28infertile car stereotype analysis is the
204. 8:30only way to diagnose Turner syndrome it
205. 8:33can be done before birth by chonic Villa
206. 8:36sampling or
207. 8:38amniocentesis other tests can be useful
208. 8:40for identifying the specific
209. 8:41developmental abnormalities caused by
210. 8:43Turner syndrome that may be affecting
211. 8:45the person for example an ultrasound can
212. 8:48show congenital issues like cystic
213. 8:50hygroma cardiac defects and Horseshoe
214. 8:53kidney and a fasting blood glucose test
215. 8:56can help detect
216. 8:58diabetes treatment for Turner syndrome
217. 9:00usually involves growth hormone therapy
218. 9:02in childhood to promote height and bone
219. 9:05growth and sex hormone replacement
220. 9:07therapy starting at adolescence to
221. 9:09promote breast and uterine development
222. 9:12invitro fertilization can make pregnancy
223. 9:14possible for some females with turner
224. 9:16syndrome who are
225. 9:17infertile all right as a quick recap
226. 9:20Turner syndrome is a chromosomal
227. 9:22disorder where One X chromosome is
228. 9:24either completely or partially absent
229. 9:27the most common kot types are a 40 5x
230. 9:30and a combination of a
231. 9:3246xx and 45x Mosaic and the impact of
232. 9:36the disorder on the growth and
233. 9:37development depends on the proportion of
234. 9:39cells affected and on the amount of X
235. 9:42chromosome that's missing the most
236. 9:44common features includes streak ovaries
237. 9:46short stature lymphadema neck webbing
238. 9:50and congenital heart and renal
239. 9:52defects treatment involves growth
240. 9:54hormone therapy and sex hormone
241. 9:56replacement therapy
242. 10:18helping current and future clinicians
243. 10:20Focus learn retain and Thrive learn more