les_3_08102009 - monogenic inheritance - Mendelian...

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monogenic inheritance - Mendelian characters monogenic vs. multifactorial inheritance Mendelian pedigree patterns special features and complications to Mendelian pedigrees
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monogenic inheritance phenotype depends on the genotype at a single locus mostly a qualitative assessment: trait is present or absent characters: ‘Mendelian’ one gene – one peptide ↔ one gene – one syndrome locus heterogeneity: determination of a disease or phenotype by mutations at different loci allelic heterogeneity: many different disease causing alleles at a single locus clinical heterogeneity: 2 or more diseases caused by mutations in a single gene
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monogenic vs. multifactorial oligenic or polygenic dichotomous (cancer, diabetes, …) or continuous characters (weight, height, intelligence, …) conditions or traits that ‘run in the family’ - but lack a Mendelian pattern
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monogenic vs. multifactorial
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OMIM: On-line Mendelian Inheritance in Man OMIM - http://www.ncbi.nlm.nih.gov/sites/entrez?db=OMIM a catalog of human genes and genetic disorders unique six-digit number: 1-----: autosomal loci (entries created before May 15, 1994) 2-----: autosomal loci (entries created before May 15, 1994) 3-----: X-linked loci or phenotypes 4-----: Y-linked loci or phenotypes 5-----: mitochondrial loci or phenotypes 6-----: autosomal loci (entries created after May 15, 1994) symbols: *: a gene of known sequence. #: a descriptive entry (usually a phenotype) +: the description of a gene of known sequence and a phenotype. %: a confirmed mendelian phenotype for which the underlying molecular basis is not known
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monogenic diseases ~6.000 monogenic disorders autosomal: ~5.500 X-linked: ~500 Y-linked: ~10 number of loci and diseases: still increasing Mendelian inheritance patterns informative in estimating recurrence risks
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constructing a pedigree
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kinship first degree relatives: 50% genes shared
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kinship second degree relatives: 25% genes shared
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kinship third degree relatives: 12.5% genes shared
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5 basic Mendelian pedigree patterns frequent: autosomal dominant autosomal recessive X-linked recessive rare: X-linked dominant Y-linked
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autosomal dominant inheritance dominant: phenotype in heterozygote dominance: property of a character - not of a gene vertical transmission: condition is present in all generations autosomal dominant conditions: NF1, Marfan syndrome, achondroplasia, Huntington disease, Steinert disease (myotonic dystrophy), hereditary breast cancer, hereditary colorectal cancer recurrence risk: 50%
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autosomal dominant inheritance
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autosomal recessive inheritance recessive: phenotype in homozygotes or compound heterozygotes horizontal transmission: condition can be present in siblings, usually not in earlier generations
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les_3_08102009 - monogenic inheritance - Mendelian...

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