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41 Cards in this Set

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Pt w/rapid loss of vision in he central visual field as a result of optic nerve death. Vision loss is in the 3rd decade of life and is irreversible. This runs in the family. The mutation is a missense mutation in the mtDNA.
Leber hereditary optic neuropathy (LHON)
Pt w/epilepsy , dementia, ataxia, and myopathy. Caused by a single base mutation in a mtDNA tRNA gene.
Myoclonic epilepsy with ragged red fibers
What disease is caused by a single-base mutation in tRNA mitochondria?
Mitochondrial encephalomyopathy and stroke like episodes (MELAS)
What are the mitocondrial disorders
1. Leber hereditary optic neuropathy (LHON), 2. myoclonic epilepsy with ragged red fibers (MERRF), 3. mitochondrial encephalomyopathy and stroke-like episodes (MELAS), 4. kearns-sayre disease, 5. pearson syndome, 6. chronic progressive external opthalmoplegia
What is leber hereditary optic neuropathy(LHON)
Optic nerve death in 3rd decade, heteroplasmy uncommon, MISSENSE mutation in protein coding genese
What is myoclonic epilepsy with ragged red fibers (MERRF)
Single base changes in tRNA, epilepsy, ataxia, dementia, myopathy, heteroplasmic, highly variable expression
What is mitochondrial encephalomyopathy and stroke-like episodes(MELAS)
Single-base mutation in tRNA, heteroplasmic w/variable expression
What are the mitochondrial disorders due to duplications and deletions in the mitochondrial chromosome
1. Kearns-sayre disease, 2. pearson syndrome, 3. chronic progressive external opthalmoplegia
Some dominant disorders are more severe in later generations (ie myotonic dysrophy or huntingtons chorea)
What is the MOA of huntingtons?
Repeated codon sequence expansion (CAG) glutamine -> occurs during meiosis(greater number can cause earlier and/or more severe disorder)
Inheritance pattern of myotonic dystrophy
Anticepation -> every generation gets the disease earlier and earlier age
Fragile X-syndrome
Most common inherited form of mental retardation (down syndrome is more common but not inherited)
Cells that are in culture but end of long arm of X-breaks in low folic aicd
The sherman paradox
Normal transmitting males occur -> not affected, but have affected descendants
Pt w/ long face, prominent jaw, large ear
Genomic imprinting
Certain genes are only expressed (inherited from mom or dad)
Which disease sees a deletion from dad?
Prader willie
Which disease sees a maternal deletion?
Fragile X-inheritance pattern
Transmitting numbered copied repeats -> greater than 230 is abnormal
Dosage compensation
Dosage compensation is a genetic regulatory mechanism which operates to equalize the phenotypic expression of characteristics determined by genes on the X chromosome so that they are equally expressed in the human XY male and the XX female
What is the lyon hypothesis?
One X chromosome in each XX cell is inactivated -> barr body is seen in nucleus
What are the rules of X-inactivation
1. Inactivation is random, fixed, and incomplete
X-inactivation center
XIST gene on the X-chromosome -> transcribes 17kb RNA from inactivated X-chromosome -> coats inactive X (maintains inactivation) -> methylation = high + histone = deacetylation
What are the X-linked disorders we need to know?
1. Hemophilia A, 2. duchenne's muscular dystrophy, 3. red-green color blindness
What is the hardy-weinberg expression of males in x-linked recessive? Females?
Males = q, females = q^2
What is unique about x-linked recessive pedigrees
No father -> son transmission or passage thru females is a skipped generation; affect father + normal mother = no affected children
What are the characterisitcs of hemophilia A?
Factor VIII deficiency (X-chromosome) -> results in prolonged bleeding from wounds, hemorrhages in joints and muscles(hemearthrosis) -> intracranial bleeding -> death
What type of mutations occur in the Factor VIII gene?
Non-sense, deletion, inversion = severe; missence = mild
5 yo Pt w/severe muscular arophy, clumsy, weak-> heart/respiratory muscles impaired, Creatinine kinase released by msucle -> cardiac/respiratory failure by 25 yo
Duchenne muscular dysrophy
What does the DMD protein do?
On cytoplasmic side of membrane -> involved in cytoskeltal integrity -> binds F-actin and dystroglycan (in membrane)
What disease is the altered function of dystrophin?
Beckers muscular dystrophy
What is the MOA for color blindness?
Opsin proteins absorb colors -> red + green opsins are adjacent on X-chromosome thus can affect both at same time (caused by unequal crossing over)
Define: deuteranopia
No green vision
No red vision
What is the mode of transmission for x-linked dominant inheritance
Males get from mother, females get from either parent
What are the x-linked dominant disorders
1. Hypophosphatemic rickets, 2. incontinetia pegmenti, 3. rett syndrome
Hypophosphatemic rickets
Kidnesy cant reabsorb phosphate, abnormal ossification -> bones bend and distort (x-linked dominant)
Incontinentia pigmenti
Abnormal skin pigmentation + teeth, neurological and ocular abnormalities, males losst in utero(x-linked dominant)
Rett syndrome
Autism, ataxia, mental retardation, some males survive to term (x-linked dominant)
Holandric inheritance
Y-chromosome inheritance-> father to son transmission; most genes involved w/sex determination, spermatogenesis, testicular function; X-Y crossing -over occur in this region
What is unique about mitochondrial inheritance
Circular chromosome, produces its own ribosomes and tRNAs, Inheritance = maternal(from the mom only), mutation rate = high -> lacks repair systems