Genetic Disorders & Inborn Errors Of Metabolism Flashcards
What are the classic mendelian disorders?
- Autosomal dominant
- Autosomal recessive
- X-linked dominant
- X-linked recessive
Which mendelian disorder is more severe or lethal in males while affected females have a 50% risk of having an affected daughter?
X-linked dominant
What are unstable repeat sequences?
Occur when the number of specific nucleotide copies within a gene increases, resulting in increased disease severity
What is uniparental disomy?
Occurs when instead of inheriting one gene or chromosome from each parent, both members of a chromosome or gene pair are inherited from same parent
What is genomic imprinting?
Occurs when a gene defect is expressed solely based on the sex of the parent passing on the defective gene
If a mother passes on an abnormal 11q region on chromosome 15, the offspring will have…
Angelman Syndrome
If a father passes on an abnormal 11q region on chromosome 15, the offspring will have…
Prader Willi syndrome
What are the differences between malformation, deformation, or disruption?
- Malformation: Occurs when an intrinsically abnormal process forms abnormal tissue
- Deformation: Occurs when mechanical forces are exerted on normal tissues
- Disruption: Occurs when normal tissue becomes abnormal after being subjected to destructive forces
What is a syndrome?
Occurs when a collection of seemingly unrelated abnormal features occur in a familiar pattern
What causes increased maternal α-fetoprotein?
- Fetal neural tube defects
- Multiple gestation pregnancies
- Underestimated gestational age
- Ventral abdominal wall defects
- Fetal demise
What are the three markers in a triple screen?
What is indicated if there is low AFP, low unconjugated estriol, and high ß-HCG?
What if all three are low?
- AFP
- Unconjugated estriol
- ß-HCG
Down syndrome; trisomy 18
When is Chorionic villus sampling (CVS) done for genetic evaluation of a fetus?
When can amniocentesis be done?
10-13 weeks
16-18 weeks
Marfan syndrome is an autosomal ______ disorder
What gene defect is associated with Marfan syndrome?
Autosomal dominant
The gene defect has been mapped to a region on chromosome 15 that codes for fibrillin
What are the clinical features of Marfan syndrome?
Skeletal findings:
Occular findings:
Cardiovascular findings:
- Skeletal findings: tall stature with elongated extremities and long fingers
- Occular findings: upward lens subluxation
- Cardiovascular findings: Aortic route dilatation
What disorder has many of the same clinical features as Marfan’s syndrome and must be ruled out
Homocystinuria
What are some complications of marfan’s syndrome?
Endocarditis, retinal detachment, and sudden death as a result of aortic dissection
What are some clinical features of Prader-Willi syndrome?
- Craniofacial: Almond-shaped eyes; fishlike mouth
- Failure to thrive; obesity as a result of hyperphagia later in childhood
- Hypotonia, mental retardation
- Hypogonadism
What are the clinical features of angelman syndrome?
- Neurologic findings include jerky arm movements, ataxia, and paroxysms of inappropriate laughter
- Craniofacial findings include a small wide head, large mouth with widely spaced teeth, tongue protrusion, and prognathia
What is Noonan syndrome?
“male version of Turner syndrome”
What are the clinical features of Noonan syndrome?
- Short stature and a shield chest
- Short webbed neck and low hairline
- Right-sided heart lesions, most commonly pulmonary valve stenosis
- Mental retardation in 25%
What two distinct syndromes have a deletion at chromosome 22q11?
DiGeorge syndrome
Velocardiofacial syndrome
What is CATCH-22?
A name describing the features of 22q11 deletions
- Cardiac anomaly
- Abnormal facies
- Thymic hypoplasia
- Cleft palate
- Hypocalcemia
- Gene defect on chromosome 22
DiGeorge syndrome is caused by a defect in the structures derived from the ____ and _____ pharyngeal pouches
third and fourth
THymus and parathyroid hypoplasia in DiGeorge syndrome cause…
cell-mediated immunodeficiency and severe hypocalcemia
What is Ehler-Danlos syndrome?
What type of inheritance is it?
Characterized by the production of defective type V collagn resulting in hyerextensible joints, fragile vessels, and loose skin
Autosomal dominant
What are the cardiovascular findings in Ehler-Danlos syndrome?
Mitral valve prolapse, Aortic root dilatation, and fragile blood vessels that result in ease of bruising
What is osteogenesis imperfecta?
Results from mutations that cause production of abnormal type I collagen
What are the clinical features of Type I Osteogenesis Imperfecta?
- Blue sclerae
- Skeletal findings such as fragile bones
- Yellow or gray-blue teeth
- Easy bruisability
What are some complications of Ehler Danlos syndrome?
Early conductive hearing loss
Skeletal deformities as a result of fractures
What are the VACTERL anomalies?
- Vertebral defects
- Anal atresia
- Cardiac anomalies (VSDs)
- TracehoEsophageal fistula
- Renal and genital defects
- Limb defects
What are the CHARGE associations?
- Colobomas (absence/defect of ocular tissue)
- Heart defects (Tetralogy of Fallot)
- Atresia of the nasal choanae
- Retardation of growth and cognition
- Genital anomalies
- Ear anomilies (hearing loss and cup shaped ears)
What is Williams syndrome?
Notable for a unique loquacious personality often described as a “cocktail party” personality; caused by deletion on chromosome 7
What are the clinical features of Williams syndrome?
- Elfin facies
- Mental retardation and loquacious personality
- Supravalvular aortic stenosis
- Idiopathic hypercalcemia in infancy
- Conncective tissue abnormalities
What is most notable about Cornelia de Lange (Brachmann-de Lange) syndrome?
Most notable for a single eyebrow and very short stature without skeletal abnormalities
What behavioral features are associated with Cornelia de Lange (Brachmann-de Lange) syndrome?
Autistic features, lack of facial expression, and self-destructive tendencies
What is classically seen in Russel-Silver syndrome?
Short stature and skeletal asymmetry with a normal head circumference
What skin findings are associated with Russell-Silver syndrome?
Cafe-au-lait spots and excessive sweating
Pierre Robin syndrome clinical features?
Micrognathia, cleft lip and palate, and a large protruding tongue
Cri du chat syndrome is caused by a partial deletion of the short arm of chromosome __
5
What is the most common trisomy syndrome?
Down syndrome (trisomy 21)
What is the second most common trisomy syndrome? It is three times more common in ________
Trisomy 18; females
What are the general clinical features of trisomy syndromes?
- Mental retardation and hypertonia with scissoring of the lower extremities
- Delicate, small facial features
- Clenched hands with overlapping digits, rocker bottom feet
- Trident shaped hands
________ is 20 times more common in Down Syndrome than in general population
Leukemia
How are trisomy syndromes diagnosed?
Chromosomal analysis
What are the clinical features of Turner syndrome?
- Short stature
- Webbed neck
- Shield chest
- Swelling of the dorsum of hands and feet
- Ovarian dysgenisis
What cardiac effects are associated with Turner syndrome?
- Left-sided heart lesions
- Coarcatation of the aorta
- Bicuspid aortic valve
- Hypoplastic left heart
Fragile X syndrome is an X-linked disorder caused by a site on the X chromosome that contains a variable number of ____ repeats
CGG
What type of inheritance pattern is associated with Fragile X syndrome?
Anticipation
What is the most common inherited cause of mental retardation?
Fragile X syndrome
What are some clinical features of Fragile X syndrome?
- Mild to severe mental retardation
- Large ears
- Large testes develop during puberty
- Emotional instability
What is the most common cause of male hypogonadism and infertility?
Klinefelter syndrome