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Figure A
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Figure B
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Figure C
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Figure D
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Figure E
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Patau's syndrome (trisomy 13) can be identified on a karyotype by the presence of 3 chromosome at location 13, as seen in Figure C. Patau's syndrome is characterized by an extra copy of the 13th chromosome causing trisomy 13. It is usually fatal, and death typically occurs within 1 year of birth. Findings include severe mental retardation, microphthalmia, microcephaly, cleft lip, cleft palate, holoprosencephaly, polydactyly, and congenital heart disease. The characteristic results of the first trimester pregnancy screen include decreased free B-hCG, decreased PAPP-A, and increased nuchal translucency on ultrasound. Edwards syndrome also presents with decreased B-hCG and decreased PAPP-A, but would not present with polydactyly but rather other limb abnormalities (webbing of toes, clubfoot, absent radius, etc.) Kroes et al. describe the ultrasound features of trisomy 13 (Patau syndrome) and trisomy 18 (Edwards syndrome) in a consecutive series of 47 cases. They find that the most common malformations in trisomy 13 were craniofacial defects, cerebral malformations, and genitourinary tract anomalies. The most common malformations associated with trisomy 18 were limb abnormalities (other than polydactyly) and intrauterine growth restriction. Odeh discusses the best way to diagnose both trisomy 13 and 18. He states that most studies show that the new cell free fetal DNA (cffDNA) techniques have a certain percentage of false positive and false negative rates, with different detection rates depending on the method used to analyze the fetal DNA. Thus, he recommends conventional screening methods should be applied, and suspected cases should be karyotyped using an invasive test until more experience is gained with using cffDNA tests. Figures A-E are described below in the incorrect answer explanations. Incorrect answers: Answer 1: Figure A demonstrates the karyotype of a normal male. Answer 2: Figure B demonstrates the karyotype of Down Syndrome (trisomy 21). Down syndrome demonstrates decreased a-fetoprotein, increased B-hCG, decreased estriol, and increased inhibin A on quad screen along with increased nuchal translucency on ultrasound. Answer 4: Figure D demonstrates the karyotype of Edward's syndrome (trisomy 18). Edward's syndrome demonstrates decreased a-fetoprotein, decreased B-hCG, decreased PAPP-A, decreased estriol, and normal inhibin A on quad screen. However, Edward's syndrome is not associated routinely with polydactyly. Answer 5: Figure E demonstrates the karyotype of a normal female.
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