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Genetics for USMLE

What is pleiotropy? One gene has more than effect on an individual's phenotype. PKU causes many seemingly unrelated symptoms
What is imprinting? Differences in phenotype depend on whether the mutation is maternal or paternal. Prader-Willi and Angelmann's syndromes are ex
Huntington's disease shows Anticipation
If a patient develops a mutation in a tumor suppressor gene, the complimentary allele must be mutated or deleted before cancer develops Loss of heterozygosity (ex Retinoblastoma)
A heterozygote produces a non-functional altered protein that also prevents the normal gene product from functioning Dominant negative mutation
Tendency for certain alleles at 2 linked loci to occur together more often than expected by chance Linkage disequilibrium
random X inactivation in females Lyonization
An individual derived from 2 zyogtes that subsequently fuse Chimeric individual
Mutations at different loci can produce the same phenotype Locus heterogeneity- Marfan's, MEN2B, homocystinuria all cause marfanoid habitus
Presence of both normal and mutated mitochondrial DNA resulting in variable expression in mitochondrial inherited disease Heteroplasmy
At some loci, only one allele is active and the other is inactive. The active allele is deleted and the other is inactivated (by methylation) Imprinting
A mentally retarded person with hyperphagia, obesity, hypogonadism and hypotonia has a normally inactivated maternal allele. Paternal allele should be active but is deleted Prader-Willi (P for Paternal)
Mental retardation, seizures, ataxia, innapropriate laughter because of normally inactive paternal allele and deletion of maternal allele. AngelMAN's syndrome
Cell signaling defect of fibroblast growth factor 3. Dwarfism, short limbs, head and trunk normal. Advanced paternal age. Achondroplasia
Bilateral massive enlargement of kidneys, berry aneurysms, MVP Autosomal Dominant polycystic kidney disease
Colon becomes covered with adenomatous polyps after puberty, progresses to colon cancer. Familial Adenomatous polyposis, chromosome 5
Elevated LDL due to defective or absent receptor. Heterozygotes have cholesterol 300, Homozygotes above 700. Tendon xanthomas, MI before age 20. Familial Hypercholesterolemia
Telangiectasia, recurrent nosebleeds, skin discolorations, AV malformations Hereditary hemorrhagic telengiectasia (Osler-Weber-Rendu syndrome)
Spheroid erythrocytes due to spectrin or ankyrin defect. Hemolytic anemia, increased MCHC, splenectomy is curative Hereditary spherocytosis
Huntington's disease is located on what chromosome? Chromosome 4 (hunting 4 food)
Tall person with long extremities, pectus excavatum, hyperextensive joints, cystic medial necrosis of aorta, dissecting aortic aneurysm subluxation of lenses Marfans
MEN2A and 2B are associated with what gene? ret gene
cafe-au lait spots, neural tumors, lisch nodules *pigmented iris hamartomas*, scoliosis, optic pathway gliomas Neurofibromatosis 1, on long arm of Chr 17
Bilateral acoustic schwannomas, juvenile cataracts NF2 on Chromosome 22 (type 2 is B/L and on 22)
Facial lesions, adenoma sebaceum, hypopigmented ash leaf spots on skin, cortical and retinal hamartomas, seizures, retardation, renal cysts, astrocytomas Tuberous sclerosis
Bilateral Renal cell carcinoma, hemangioblastomas of retina/cerebellum/medulla. Von Hippel-Lindau disease
Von Hippel-Lindau disease is caused by what? Deletion of VHL gene on chromosome 3 (3 letters). Results in constitutive expression of HIP transcription factor and activation of angiogenic growth factors.
X-linked frame shift mutation resulting in deletion of dystrophin gene--> accelerated muscle breakdown. Weakness in pelvic girdle muscles. Pseudohypertrophy of calf muscles, cardiac myopathy. Onset before age 5 Duchenne's. Deleted dystrophin. Longest human gene and inc rate of spontaneous mutation
X-linked mutation in dystrophin gene that presents in adolescence Becker's muscular dystrophy
What causes infertility in males due to bilateral absence of vas deferens CF
Trinucleotide repeat expansion diseases are Huntingtons, myotonic dystrophy, Friedreich's ataxia and fragile X
What is an X-linked defect affecting methylation and expression of FMR1 gene? Fragile X
What is the second most common cause of mental retardation? Fragile X
Enlarged testes, long face with a large jaw, large everted ears, autism, MVP Fragile X
What pattern of inheritance is due to defects in structural genes, many generations and both males and females affected, presents clinically after puberty? Autosomal dominant
Often due to enzyme deficiencies, usually seen in only one generation, presents in childhood Autosomal recessive
No male to male transmission X linked
All offspring of father are affected X linked dominant
Hypophosphatemic rickets is inherited how? X linked dominant, formerly called vit-D resistant rickets. Increased phosphate wasting at proximal tubule.
All offspring of affected females show signs of disease. Often due to failures of oxidative phosphorylation Mitochondrial inheritance
leber's hereditary optic neuropathy (acute loss of central vision) is transmitted how? Mitochondrial
Myoclonic epilepsy is transmitted how? Mitochondrial
Decreased alpha fetoprotein, increased B-HCG, decreased estriol and increase in inhibin A, increase in nuchal translucency Down's Syndrome
What congenital heart disease is associated with Down's? Septum primum ASD
What are other comorbidities of Down's? ALL and Alzheimer's
Severe mental retardation, rocker-bottom feet, micrognathis (small jaw), low set Ears, clenched hands Edwards syndrome. Election day 18-trisomy 18
What syndrome for decreased alpha-fetoprotein, decreased B-HCG, decreased estriol and normal inhibin A? Edwards Syndrome (trisomy 18)
Severe mental retardation, rocker bottom feet, micro-opthalmiam microcephaly, cleft lip, holoprosencephaly, polydactyly Patau's syndrome (trisomy 13) Puberty=13 Normal B-HCG, normal estriol, normal inhibin A
VSD, mental retardation, epicanthal folds, microdeletion of short arm of chromosome 5 Cri-du-chat syndrome
microdeletion of long arm of chromosome 7, elfin facies, mental retardation, hypercalcemia, well developed verbal skills, friendly with strangers Williams syndrome
Aberrant development of 3rd and 4th branchial arches 22q11 deletion: DiGeorge and Velocardiofacial syndrome
What is seen clinically with DiGeorge? Cleft palate, abnormal facies, thymic aplasia, cardiac defects, hypocalcemia (secondary to parathyroid aplasia)
Created by: tessah10



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