Page 108 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

64 SECTION II BIOCHEmISTRY ``BIOCHEMISTRY—GENETICS BIOCHEmISTRY ``BIOCHEMISTRY—NUTRITION

Genetic disorders by CHROMOSOME SElECTED EXAMPlES
chromosome 3 von Hippel-Lindau disease, renal cell carcinoma
4 ADPKD (PKD2), achondroplasia, Huntington disease
5 Cri-du-chat syndrome, familial adenomatous polyposis

6 Hemochromatosis (HFE)
7 Williams syndrome, cystic fibrosis
9 Friedreich ataxia, tuberous sclerosis (TSC1)
11 Wilms tumor, β-globin gene defects (eg, sickle cell disease, β-thalassemia), MEN1
13 Patau syndrome, Wilson disease, retinoblastoma (RB1), BRCA2
15 Prader-Willi syndrome, Angelman syndrome, Marfan syndrome
16 ADPKD (PKD1), α-globin gene defects (eg, α-thalassemia), tuberous sclerosis (TSC2)
17 Neurofibromatosis type 1, BRCA1, TP53
18 Edwards syndrome
21 Down syndrome
22 Neurofibromatosis type 2, DiGeorge syndrome (22q11)
X Fragile X syndrome, X-linked agammaglobulinemia, Klinefelter syndrome (XXY)

Robertsonian Chromosomal translocation that commonly involves chromosome pairs 21, 22, 13, 14, and 15.
translocation One of the most common types of translocation. Occurs when the long arms of 2 acrocentric
chromosomes (chromosomes with centromeres near their ends) fuse at the centromere and the
2 short arms are lost.
Balanced translocations normally do not cause any abnormal phenotype. Unbalanced
translocations can result in miscarriage, stillbirth, and chromosomal imbalance (eg, Down
syndrome, Patau syndrome).

Cri-du-chat syndrome Cri du chat = cry of the cat. Congenital deletion on short arm of chromosome 5 (46,XX or XY,
5p−).
Findings: microcephaly, moderate to severe intellectual disability, high-pitched crying/meowing,
epicanthal folds, cardiac abnormalities (VSD).

Williams syndrome Congenital microdeletion of long arm of chromosome 7 (deleted region includes elastin gene).

A Findings: distinctive “elfin” facies A , intellectual disability, hypercalcemia, well-developed verbal
skills, extreme friendliness with strangers, cardiovascular problems (eg, supravalvular aortic
stenosis, renal artery stenosis). Think Will Ferrell in Elf.

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