msyamp
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1. A 24-year-old woman with myotonic dystrophy has significant muscle weakness and wasting. She has a one-year-old son with very poor muscle tone and severe weakness and significant development delay. Her affected 55-year-old father has cataracts but no muscle weakness.D. Anticipation
2. A man and woman, each of whom has autosomal recessive congenital deafness, have four biological children, each of whom has normal hearing. Locus heterogeneity
3. A 40-year-old man with neurofibromatosis (NF1) has a plexiform neurofibroma of his leg that has caused significant disfigurement, and hundreds of cutaneous neurofibromas. His 43-year-old sister has cafe-au-lait spots and Lisch nodules of the iris, but no neurofibromas. His 19-year-old son has cafe-au-lait spots, a dozen cutaneous neurofibromas, and scoliosis (curvature of the spine).Variable expressivity
Edited by msyamp on 02/05/06 - 04:30 PM
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| msyamp
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About 10% of pheochromocytomas (a tumor of the adrenal medulla) occur in patients with familial cancer syndromes, one of which is multiple endocrine neoplasia syndrome, type II (MEN-II). In most MEN-II families, there are germline mutations in the RET gene, located on chromosome 10. Most commonly, these mutations are in one of several different codons encoding cysteines. This is an example of:Allelic heterogeneity
. MEN-II is an autosomal dominant cancer syndrome. Another autosomal dominant cancer syndrome associated with pheochromocytomas (and occasionally misdiagnosed as MEN-II) is von Hippel-Lindau disease, the gene for which is on chromosome 3. With regard to familial pheochromocytomas, these two diseases are examples of Locus heterogeneity
95% of individuals affected with MEN-II have thyroid C-cell hyperplasia and medullary thyroid carcinoma, 50% have pheochromocytoma, and about 20% have hyperparathyroidism. This is an example of:Variable expressivity
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| msyamp
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Retinoblastoma has a penetrance of about 75% (incomplete penetrance) - only about 3/4 of the individuals with the genotype for retinoblastoma susceptibility actually get the disease. On the other hand, the dominantly inherited neurodegenerative disease Huntington's disease has a penetrance of 100% (complete penetrance) - everyone with at least one copy of the Huntington's allele will get the disease
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| Geroo
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great msyamp ,thanks.
what about genetic heterogeneity?
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| msyamp
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genetic heterogenety is of two types.
1. allelic
2. locus
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| Geroo
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oh ok,so it's the big term.thanks msyamp...
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