Biochem15 Flashcards
Autosomal Trisomies
Down syndrome is trisomy ___.
21 (1:700)
Down’s - Drinking age - 21
What are some characteristic findings in trisomy 21?
Simian crease Duodenal atresia Congenital heart dz INcreased risk for ALL & Alzheimer's (>35 y/o) Prominent epicanthal folds Gap btwn 1st 2 toes
95% if trisomy cases are due to what?
Meiotic nondisjunction of homologous chromosomes
Trisomy 21 is associated with advanced maternal age. 1:___ in women 45.
1:1500 45
4% of trisomy 21 cases are due to what?
Robertsonian translocation
In trisomy 21 cases what are the results of the pregnancy quad screen?
DECREASED: alpha-fetoprotein & estriol
INCREASED: beta-hCG & inhibin A
What does ultrasound show in trisomy 21 cases?
INcreased nuchal in first trimester translcency
Edwards’ syndrome is trisomy ___.
18 (1:8000)
Edwards - Election age - 18
What are the findings in Edwards’ syndrome (trisomy 18)?
Severe mental retardation rocker-bottom feet Micrognathia (small jaw) Low-set Ears Clenched hands Prominent occiput congenital heart dz
Death usually occurs within 1 year of birth
In trisomy 18 cases what are the results of the pregnancy quad screen?
DECREASED:
- alpha-fetoprotein
- beta-hCG
- estriol
NORMAL: inhibin A
Patau’s syndrome is trisomy __.
13 (1:15,000)
“Patau - Puberty - 13”
What are the findings in Patau’s syndrome (trisomy 13)?
Severe mental retardation rocker-bottom feet micropthalmia microcephaly cleft liP/Palate holoProsencephaly Polydactyly congenital heart disease
Death usually occurs within 1 year of birth
What are the results of first-trimester pregnancy screen in Patau’s syndrome cases?
DECREASED:
- beta-hCG
- PAPP-A
INCREASED:
- nuchal translucency
What is Robertsonian translocation?
Nonreciprocal chromosomal translocation that commonly involves chromosome pairs 13,14,15,21,22
One of the most common types of translocations
When do Robertsonian translocations occur?
When long arms of 2 acrocentric chromosomes fuse at the centromere and the 2 short arms are lost
What are an acrocentric chromosomes?
chromosomes with centromeres near their ends
In Robertsonian translocations, do balanced or unbalanced translocations result in miscarriage, stillbirth, and trisomies?
Unbalanced
Balanced normally do not cause any abnormal phenotypes
What causes Cri-du-chat syndrome?
Congenital microdeletion of short arm of chromosome 5
46,XX or XY, 5p-
What are the findings in Cri-du-chat syndrome?
Microcephaly mod-severe retardation High pitched crying/mewing epicanthal folds cardaic abnormalities (VSD)
“Cri du chat = cry of the cat”
What syndrome is associated with a congenital microdeletion of long arm of chromosome 7?
What gene is in the deleted region?
Williams syndrome
elastin gene
What are the findings in WIlliams syndrome?
"Elfin" facies Intellectual disability hypercalcemia (INcreased sensitivity to Vit. D) Well-developed verbal skills Extreme friendliness w/ strangers cardiac abnormalities
What are the potential presentations of 22q11 deletion syndromes?
“CATCH-22”
Cleft palate Abnormal facies Thymic aplasia --> T-cell deficiency Cardiac defects Hypocalcemia 2dary to parathyroid aplasia
d/t microdeletion at chromosome 22q11
22q11 deletion syndromes are due to what?
Aberrant development of 3rd & 4th branchial pouches
What defects are seen in DiGeorge syndrome?
Thymic, Parathyroid and Cardiac defects
