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Firstaid BiochemA
Genetics
| Question | Answer |
|---|---|
| What is pleitropy | one gene affects more than one phenotypic trait (e.g. PKU causes hair and skin changes as well as MR) |
| What is imprinting | Phenotypic difference depending on whether gene is maternal or paternal in origin (prader-willi, angelman's) |
| What is anticipation | severity worsens by generation |
| Which type of genes are concerning for loss of heterozygosity | tumor supressor genes (not oncogenes) Rb, p53 |
| What is a dominant negative mutation | mutated protein product also prevents wild type from functioning |
| What is linkage disequilibrium | alleles at two linked loci occur together more often than would be expected by chance, usually considered on a population scale |
| What is lyonization | a type of mosaicism involving random X inactivation in females |
| What is heteroplasmy | both normal and mutated mtDNA results in variable expression in mitochondrial inherited disease |
| What is uniparental disomy | offspring gets 2 copies of chromosome from 1 parent and no copies from the other parent |
| When might uniparental disomy be suspected | a person manifests a recessive condition when only one parent is a carrier |
| What is the prevalence of an x-linked recessive disease in each sex | q in males, q^2 in females |
| What are hardy-weinburg assumptions | no mutation at the locus, no selection for genotypes at the locus, completely random mating, no migration |
| What are causes of prader willi syndrome | deletion of the normally active paternal allele on chr15, uniparental maternal disomy of chr15 |
| What are causes of Angelman's syndrome | deletion of normally active maternal allele on chr15, or uniparental paternal disomy of chr15 |
| What are features of prader-willi | MR, hyperphagia, obesity, hypogonasidm, hypotonia |
| What are features of Angelman's | MR, seizures, ataxia, inappropriate laughter ("happy puppet") |
| What type of inheritance is associated with more severe and earlier presentation | AR |
| How is hypophosphatemic rickets usually inherited | x-linked dominant |
| What diseases show mitochondrial inheritance | mitochondrial myopathies, leber's hereditary optic neuropathy (acute loss of central vision) |
| What causes achondroplasia | Fibroblast growth factor cell-signalling defect; also associated w/advanced paternal age |
| What is autosomal-dominant polycystic kidney disease | ALWAYS BILATERAL; flank pain, hematuria, and progressive renal fialure, 90% due to APKD1 mutation on chromosome 16 (infantile is recessive though) |
| What are associated features with polycystic kidney disease | polycystic liver disease, berry aneurysm, mitral valve prolapse |
| What causes familial adyenomatous polyposis | chromosome 5 APC gene delted (5 leters in polyp) |
| What causes familial hypercholesterolemia | defective or absent LDL receptor; heterozygotes LDL>300, homozygote LDL>700!, causes severe atherosclerotic dz and tendon xanthomas, MI beore age 20 (!!!) |
| What is hereditary hemorrhagic telangiectasia | also called osler-weber-rendu syndrome, causes telangiectasias, recurrent epistaxis, skin discoloration, and AVM |
| What is hereditary spherocytosis | defects in ankrin or spectrin causes hemolytic anemia and increased MHCH, can cure w/splenectomy |
| What brain findings are associated with huntington's diesase | decreased GABA, Ach in the brain, atrophy of the caudate, |
| Where is the Huntington gene located | chromosome 4 |
| What is MEN | multiple endocrine neoplasia, tumors in pancreas, parathyroid, pituitary, thyroid, and adrenals; sometimes associated with ret gene |
| What causes marfans | fibrillin mutation--->arachnodactyli, hyperextensive joints, pectus excavatum, tall/long extremities, cystic medial aortic necrosis, floppy mitral valve, subluxation of lenses |
| What are findings in NF1 | café au lait, neural tumors, lisch noduels in the iris, skeletal disorders, optic pathway gliomas, pheochromocytoma, tumor susceptibility, Long arm of chromosome 17, =von recklinghousen |
| What are findings in NF2 | bliateral acoustic neruoma, juvenile cataracts, NF2 gene mutation on chr22 |
| What is tuberous sclerosis | facial lesions (adnoma sebaceum), hypopigmented ash leaf spots on skin, cortical and retinal hamartomas, seizures, MR, renal cysts/renal angiomyolipomas, cardiac rhabdomyomas, increased astrocytoma incidence |
| What are genetic features of tuberous sclerosis | incomplete penetrance and variable presentation |
| What are features of von Hippel-Lindau disease | causes hemangioblastomas, renal cell carcinoma, other tumors due to VHL tumor supressor deletion on chromosome 3p. |
| What is the cause of VHL | VHL loss -->constitutively active HIF transcription factor-->angiogenic growth factor activation |
| What infections are particularly problematic in CF patients | pseudomonas and S aureus |
| Why do male CF patients experience infertility | bilateral congenital absence of vas deferens |
| How is CF dxed | increased concentration fo CL- ions in sweat |
| What is treatment of CF N-ac to loosen mucous plugging (cleaves disulfide bonds w/in mucous glycoproteins) | |
| What diseases are x-linked recessive | bruton's agammaglobulinemia, wiskott-aldrich, fabry's, G6PD deficiency, ocular albinism, lesch-mnyhan, duchenne's beckers, Hemophilia A/B, Hunter's syndrome |
| What causes Duchenne's | x-linked frameshift mutation-->dystrophin absent-->accelerated muscle breakdown (gower's maneuver, pseudohypertrophy of calf muscles, cardiac myopathy) |
| What is becker's less severe than Duchenne's, also X-linked dystrophin problem | |
| Why is duchenne likely to come from a spontaneous mutation | longest known human gene-->increased spontaneous mutation rates |
| What causes fragile X | trinucleotide repeat expansion disorder; once adequately expanded, FMR1 gene is methylated so that it is not expressed, 2nd most common cause of MR after Down syndrome |
| What are fragile x findings | long face/large jaw, MR, enlarged testes, large everted ears, autism, MVP |
| What are trinucleotide repeat expansion disorders | huntington's (CAG); myotonic dystrophy (CTG); fragile X (CGG), and friedreich's ataxia (GAA) |
| In whom are anticipatory trirepeat expansion disorders expanded | women |
| What are most common heart problems in Down syndrome | septum-primum type ASD |
| What results of a pregnancy quad screen might indicate down syndrome | decreased alpha-fetoprotein; increased beta-hCG, decreased estriol, and increased inhibin A, increased nuchal translucency |
| What is trisomy 18 | Edwards' syndrome, severe MR, rocker bottom feet, micrognathia, low ears, clenched hands, congenital heart disease, death usually <1 year |
| What is Patau's syndrome | trisomy 13, severe MR, rocker bottom feet, microphthalmia, microcephaly, cleft lip/palate, holoprosencephaly, polydactyly, congenital heart disease, death usually within 1 year of birth |
| What chromosomes undergo robertsonian translocation | 13, 14, 15, 21, and 22 |
| What is a robertsonian translocation | chromosomes w/centromeres near the ends (acrocentric) fuse at the centromere and short arms are lost |
| What are chromosomal inversions | rearrangements where segment of a chromsome is reversed end to end, may decrease fertility |
| What type of inversion involves the centromere | Doesn't involve the centromere |
| What is cri-du-chat syndrome | microdeltion on short arm of chr5, causes microcephaly, oderate to severe MR, high pitched crying/mewing, epicanthal folds, cardiac abnormalities |
| What is william's syndrome | microdeletion of the long arm of chr7 containing the elastin gene, causes elfin facies, MR, hypercalcemia/inc vit D sensitivity, well developed verbalskills, friendliness to strangers, cardio problems |
| What are 22q11 deletion syndromes | Digeorge and velocardiofacial syndromes, caused by abnormal development of the 3rd and 4th branchial pouches |
| What are the symptoms of 22q11 deltions | Cleft palate, Abnormal facies, Thymic aplasia-->t-cell deficiency, Cardiac defects, Hypocalcemia 2ndary to parathyroid aplasia CATCH-22 |
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