Chromsomal Disorders Flashcards
Aneuploidy is caused by chromosomal nondisjunction in meiosis I or II
It can occur in either but is more common in meiosis I.
What are the viable aneuploidy in humans.
Trisomy 13, Trisomy 18, Trisomy 21, Monosomy X, Trisomies of the sex chromosomes
What is better tolerated trisomy or monosomy?
Trisomy is better tolerated, but most aneuploidy results in miscarriages.
What is the most common trisomy?
Trisomy 16, but viability is not seen due to miscarriages in the first trimester.
Trisomy 21: Clinical Name, Features, and Increase Risk Factors
Down Syndrome
Craniofacial features - small head, flattened nasal bridge, upslanting palpebral features and epicanthal folds, short nose, small mouth, small ears that can be low-set or posteriorly rotated.
Hypotonia
Redundancy of unchallenged skin
Single transverse palmar crease
Clinodactyly (5th finger)
Sandal gap deformity (large space between great and 2nd toe)
Increased Risk for
Congenital Heart Disease, Hearing Loss, Otitis Media, Gastrointestinal Atresias, Hirschsprung Disease, Leukemia, eye disease, obstructive sleep apnea, thyroid disease
Mild to moderate intellectual disability (IQ 35-70)
What is the reoccurrence risk of Down Syndrome?
1% until the age of 37
Trisomy 13: Features & Occurrence
Microphthalmia, Holoprosencephaly spectrum, polydactyly, heart defects, cleft lip and palate, hypotonia, profound intellectual disability
5% to 10% survive typically dying within the first days or weeks of life
Trisomy 18: Features and Occurrence
IUGR, low birth weight, abnormal head shape, congenital heart disease, micro gnat hip, micro stamina, clench fists or overlapping fingers, profound intellectual disability
5% to 10% live past their first birthday, median survival 12 days
Monosomy X: Clinical Name & Features & Occurrence
Turner Syndrome
Short stature, ovarian hypofunction or premature ovarian failure, most require hormone therapy to reach puberty, congenital heart disease, webbed neck, hearing loos, hypothyroidism, celiac disease, normal intelligence but have increase risk of nonverbal learning disabilities and behavior abnormalities
1/2500 female live births
Trisomy X: Features & Occurrence
Taller than average, variability within developmental delay (selection bias possibly many undiagnosed), hypotonia, seizures
1/1000 and transmission is rare but reported to less than 5%
47, XXY: Clinical Name, Features, Occurrence
Klinefelter Syndrome
small testes with decreased testosterone production, delayed or incomplete puberty, gynecomastia in some, reduced body hair, infertility, genital abnormalities, increased risk of breast cancer, increased risk of autoimmune disease, taller than average, variable learning disabilities
Some asymptomatic outside of fertility
1/500 - 1/1000
47, XYY: Features & Occurrence
Taller than average, normal fertility, no significant physical features, learning disabilities present, associated with autism and behavior abnormalities
1/1000 undiagnosed likely
When does trisomy become a higher risk for pregnant women?
AMA > 35
Why does Turner syndrome likelihood not increase with maternal age?
It is not derived by nondisjunction typically, it can be from a loss of a material or paternal X
Contiguous Gene Deletion Syndrome: How does it occur? How to detect? Examples (5)
Attributable to haploinsufficiency of multiple contagious diseases within a deleted region
Can be detected using high resolution chromosomal analysis (if large enough), FISH, microarray CGH
DiGeorge Syndrome, Williams Syndrome, Cri du Chat syndrome, Miller-Dieker Syndrome
