Genetics and Chromosomal Flashcards
risk of autosomal dominant disease for child with 1 affected parent
50% risk
risk of autosomal recessive disease for child with 1 affected parent
25% risk
risk of X-linked recessive disease for child when mother is carrier
50% of her daughters can be carriers
50% of her sons can be affected
50% of her offspring can be normal
25% of her offspring will manifest the disease
Etiology of Down Syndrome
trisomy of chromosome 21; maternal non-disjunction; associated with advanced maternal age
Down Syndrome Prenatal Screening Tests
quad screen: alpha fetoprotein, estriol, Hcg and inhibin A
Down syndrome hands and feet
hand: clindoactyly, single flexion crease (Simian crease), short broad hands, shortened 5th phalynx
feet: wide spaced 1st/2nd toes (“sandle toes”)
Facial characteristics of Down Syndrome
flattened face, epicanthal folds, big tongue (macroglossia), small chin (micrognathia), low set ears
Newborn with possible Down Syndrome must have ______ done before discharge.
ECHO
Neuro effects of Downs
mental retardation (mild/mod), seizures (5-10%), early Alzheimer’s and dementia (30-40yo)
Results of prenatal quad screen in Downs
Low Alpha Feto Protein
Low Unconjugated estriol
Elevated hCG
Elevated Inhibin A
Cardiac effects of Downs
50% with cardiac anomalies (ASD most common); need ECHO!!!
HEENT effects of Downs
Hearing loss, ET dysfunction (recurrent otitis media, sinusitis), early cataracts and glaucoma, Brushfield spots
trisomy 18 is called __________ syndrome.
Edwards
Phenotypic features of trisomy 18
rocker-bottom feet, clenched hand w/ overlapping fingers, hypotonia, micropthalmia (small eyes), micrognathia
Prognosis of Edwards Syndrome
only 5% live past 1 year
Trisomy 13 is called _________ Syndrome
Patau
Features of Patau Syndrome
Polydactyly
Aplasia Cutis (missing patches of skin)
Cryptorchidism (no testes in scrotum)
Equinovarus deformities
Prognosis of trisomy 13
95% die by 6 months of age due to apneic spells
XXY (extra X chromosome) called _____.
Klinefelter Syndrome
Etiology of extra X chromosome
Non-disjunction in either the sperm or egg
Increased with advanced maternal age
Klinefelter most common genetic cause of _____ in men.
infertility
Signs of XXY
present as tall, thin, socially awkward adolescent male with mild mental delays
testosterone deficiency, small penis, hypogonadism, scant pubic hair, gynecomastia
Young female comes in with absence of menses. What to do?
Pregnancy test
r/o Turner Syndrome
Most common cause of inherited mental retardation in males is ______.
Fragile X syndrome
Monosomy X or XO karyotype is _________.
Turner Syndrome
PE with XO karyotype
female, short stature, webbed neck, broad chest with widely spaced nipples, congenital lymphedema
Turner syndrome co-existing anomalies
congenital heart defect horseshoe kidneys ovarian streaks (sterile, amenorrheic)
Can Turner Syndrome patients have children?
Yes; still have uterus (IVF and hormonal therapy)
Inheritance pattern of Fragile X
X-linked dominant; mother gives to all sons
Physical findings of Fragile X
Elongated Face
Wide Protruding Ears
Flattened Nasal Bridge
Macro-orchidism
Developmental problems of Fragile X
- Mild autistic-like behavior
- ADHD
- Depressed affect, anxiety
- Mental retardation thats worse with age
- Aggressive tendencies
Tx for Fragile X
- Meds for ADD and behaviors
- Genetic counseling
Prader-Willi syndrome etiology
Gene deletions of parental chromosome 15
Characteristics of Prader-Willi
- SGA, hypogonadism, hypotonia, poor feeding as infant, small hands & feet, almond-shaped eyes, strabismus, short stature
- developmental delay, temper tantrums
- voracious appetite and obesity in childhood
Common characteristics of Angelman syndrome
Severe mental retardation, marked developmental delay, limited language skills, paroxysmal laughter, tongue thrusting
Prognathism (jaw protrudes), seizures, and abnormal gait & posturing (“happy puppet”)
Dx testing if chromosomal abnormality suspected
karyotype and fluorescent in situ hybridization (FISH)
Two most common chromosomal abnormalities of live births
- Down syndrome (1/750)
2. Klinefelter syndrome - XXY (1/800)
How are most chromosomal abnormalities managed?
supportive care, environmental and educational programs, physical therapy, etc.
