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First Aid: Biochemistry 106-111 Day 1


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nature and severity of the phenotype varies from 1 individual to another
variable expression
not all individuals with a mutant genotype show the mutant phenotype
incomplete penetrance
1 gene has more than 1 effect on an individual's phenotype
differences in phenotype depend on whether mutation is of maternal or paternal origin
severity of disease worsens or age of onset of disease is earlier in succeeding generations
mutation in tumor supressor gene, then complementary allele must be mutated before cancer develops
loss of heterozygosity
mutation that exerts a dominant effect; heterozygote produces nonfunctional altered protein that prevents normal gene product from functioning
dominant negative mutation
tendency for certain alleles at 2 linked loci to occur together; measured in a pop, not a family
linkage disequilibrium
occurs when cells in the body have different genetic makeup
random X inactivation in females
mutations at different loci can produce the same phenotye (albinism)
locus heterozygosity
what is the heterozygote prevalence according to Hardy-Weinberg equilibrium
2pq (p,q are separate alleles)
assumptions of Hardy-Weinberg
no mutations, no selection, random mating, no migration
modes of inheritance: due to defects in structural genes (often pleiotropic and presents after puberty)
modes of inheritance: often due to enzyme deficiences (often presents in childhood)
modes of inheritance: sons of heterozygous mothers have 50% chance of being affected (no male-to-male transmission)
X-linked recessive
modes of inheritance: either male or female offspring of affected mother may be affected, while all female offspring of affected father are diseased
X-linked dominant (hypophosphatemic rickets)
transmitted only through mother (may affect all offspring of affected females)
mit inheritance (leber's hereditary optic neuropathy; mitochondrial myopathies)
AD; always bilateral; massive enlargement of kidneys due to multiple large cysts
Presents with pain, hematuria, hypertension, progressive renal failure
What chromosome is the mutation in APKD1 on?
chr 16
What is APKD associated with?
polycystic liver disease, berry aneurysms, mitral valve prolapse
Stupid mnemonic for AD diseases: And Father Marfan Never kNew Timmy Von Hunt Forged His Acent
ADPKD, Familial hypercholesterolemia, Marfan's syndrome, NF1, NF2, Tuberous Sclerosis, VHL dx, Huntington's dx, Familial adenomatous polyposis, hereditary spherocytosis, achrondroplasia
elevated LDL owing to defective or absent LDL receptor
familial hypercholesterolemia (hyperlipidemia type IIA)
severe atherosclerotic disease early in life, tendon xanthomas (Achilles tendon), MI before age 20
familial hypercholesterolemia (hyperlipidemia type IIA)
fibrillin gene mutation
Marfan's syndrome
skeletal abnormalities: arachnodactyly, hyperextensive joints, and long, tapering fingers and toes
Marfan's syndrome
find dissecting aortic aneurysms and subluxation of lenses, along with skeletal abnl
Marfan's syndrome
cafe-au-lait spots, neural tumors, Lisch nodules (pigmented iris hamartomas).
NF 1
which chr for NF1?
17 (17 letters in Von Recklinghausen)
bilateral acoustic neuroma, optic pathway gliomas, juvenile cataracts
NF 2
which chr for NF2?
chr 22
adenoma sebaceum, ash leaf spots on skin, cortical and retinal hamartomas, seizures, mental retardation, renal cysts, cardiac rhabdomyomas
tuberous sclerosis
hemangioblastomas of retinal/cerebellum/medulla, half get multiple bilateral renal cell ca
VHL disease
which chr for VHL disease?
chr 3 (3 words)
depression, progressive dementia, choreiform movements, caudate atropy, decreased GABA and Ach in brain, CAG repeats
Huntington's dx
Huntington's dx affects which chr
chr 4
colon becomes covered with adenomatous polyps after puberty
familial adenomatous polyposis
which chr for FAP
chr 5 (5 letters in polyp)
spheroid erythrocytes; hemolytic anemia; increased MCHC; splenectomy is curative
hereditary spherocytosis
defect in FGFR3
mnemonic for AR diseases: Crystal And Alfred Put Those Stupid Genes Inside My Stupid Horse
cystic fibrosis, albinism, alpha-1-antitrypsin deficiency, phenylketonuria, thalassemias, sickle cell anemias, glycogen storage diseases, infant polycystic kidney disease, mucopolysaccharidoses (except Hunter's), spingolipidoses (except Fabry's), hemochromatosis
AR defect in CFTR gene on chr 7
Cystic fibrosis
defective cl- channel, secretion of abnormally thick mucus that plugs lungs, pancreas, and liver
cystic fibrosis
recurrent pulmonary infections (Pseudomonas, s. aureus), chronic bronchitis, bronchiectasis, pancreatic insufficiency, meconium ileus in newborns
cystic fibrosis
diagnostic for CF
increased concentration of cl- ions in sweat test
most common lethal genetic disease of caucasians
tx of CF
name 11 AR disorders (hint: FGHO; DHLFBW)
Fragile X, G6PD deficiency, Hemophilia A and B, Ocular albinism, Duchenne Muscular dystrophy, hunter's syndrome, lesch-nyhan syndrome, fabry's disease, bruton's aggammaglobulinemia, wiskott-aldrich syndrome
what gene is deleted in duchenne's md
dystrophin (due to frameshift mutation)
accelerated muscle breakdown, onset before 5, weakness begins in pelvic girdle muscles and progresses superiorly, pseudohypertrophy of calf muscles, Gowers' maneuver
duchenne's muscular dystrophy
dx of muscular dystrophies
increased CPK, muscle biopsies
name of disease where mutated dystrophin gene is less severe than duchenne's
defect in FMR1 gene, 2nd most common cause of genetic Mental retardation (behind Down's)
Fragile X syndrome
Associated with macro-orchidism, long face with large jaw, large everted ears, autism
Fragile X syndrome (testes, jaws, ears)
what is the triplet in Fragile X
Trinucleotide repeat expansion diseases
Huntington's disease, myotonic dystrophy, friedreich's ataxia, fragile x (may show anticipation)
7 most common congenital malformations
heart defects, hypospadias, cleft lip (w/ or w/o cleft palate), congenital hip dislocation, spina bifida, anencephaly, pyloric stenosis
Name 3 autosomal trisomies; include chromosomes and prevalence
Down's syndrome (trisomy 21, 1:700), Edward's syndrome (trisomy 18, 1:8000), Patau's syndrome (trisomy 13, 1:6000)
most common chr d/o and cause of congenital mental retardation
down's syndrome
mental retardation, flat facial profile, prominent epicanthal folds, simian crease, duodenal atresia, congenital heart disease (most common is septum primum ASD due to endocardial cushion defects)
Down's syndrome
alzheimer's disease in affected people > 35 years old, increased risk of ALL
Down's syndrome
causes of Down's syndrome
95% due to meiotic nondisjunction of homologous chrs, 4% to robertsonian translocation, 1% to Down mosaicism (no maternal association)
severe mental retardation, rocker bottom feet, low-set ears, micrognathia, congenital heart disease, clenched hands, prominent occiput. Death by 1 y.o.
Edwards' syndrome
severe mental retardation, microphthalmia, microcephaly, cleft lip/palate, abnormal forebrain structures, polydactyly, congenital heart disease, death by 1 y.o.
patau's syndrome
microcephaly, severe mental retardation, high-pitched crying/mewing, epicanthal folds, cardiac abnormalities
cri-du-chat syndrome
cri-du-chat syndrome is due to deletion of what?
22q11 syndromes
cleft palate, abnormal facies, thymic aplasia --> Tcell def, cardiac defects, hypocalcemia due to parathyroid aplasia
when is highest risk of OH
3-8 weeks of pregnancy
developmental retardation, microcephaly, facial abnormalities, limb dislocation, heart and lung fistulas
fetal alcohol syndrome
mechanism of fetal OH syndrome
inhibition of cell migration
number one cause of congenital malformations in US
fetal OH syndrome

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