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Genetics
Genetics for USMLE
| Question | Answer |
|---|---|
| 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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