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GENETIC DISEASES.
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Discusses several dominantly inherited disorders.... More...
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Paper Abstract:
Discusses several dominantly inherited disorders. Huntington's Disease. Cavernous Angioma. Von Willebrand disease. How the defective genes are inherited. Genetic linkage analysis. Population and gender affected. Symptoms. Onset of disease. Mean age. Importance of genetic screening. Effect on pregnancy and the fetus. Major signs. Technical analysis of subject.
Paper Introduction:
Offspring inherit one set of chromosomes from the mother and one from the father. Dominantly inherited genetic disorders are those in which only one copy of the gene for that disease is needed for the disease to be present (Robinson, 1999). The gene can be inherited from either parent, and any parent with that gene will also have the disease. A parent with such a gene has a 50 percent chance of passing it on to their offspring. One example of a dominantly inherited disease is Huntington's disease. The disease is caused by a defect on chromosome 4 in the gene for a protein known as Huntington, whose function is currently unknown (Berkow, Beers and Fletcher, 1997; Robinson, 1999). The defect in the gene causes a repeat of 40 or more copies of a combination of the C, A and G DNA
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The disease is mild to moderate in most patients and isusually only diagnosed when patients with the disorder sustain trauma orundergo surgery. Labauge, P., Laberge, S., Brunereau, L., Levy, C., & Tournier-Lasserve, E. J. The gene can be inherited from either parent,and any parent with that gene will also have the disease. Lancet, 352, 1892- 19 . Gale Encyl. L., & Varady, E. A., Lermont, L., Delezoide, A. (1999). Von Willebrande disease. L.,Mirtesse, V., & Brunelle, F. Von Willebrandfactor supports primary hemostasis, including platelet adherence tosubendothelium and platelet aggregation in vessels with high shear flow.It also supports secondary hemostasis (fibrin formation) in which it servesas a carrier for factor VIII (antihemophilic factor), and protects it frompremature proteolysis and clearance from the circulation. If the DNA patterns ofthe mother and the fetus do not match, it is assumed that the fetus has notinherited the Huntington's disease gene, even if the parent carries it. Saif, M. In patients whose first symptom was hemorrhage, themean age of onset was 25.2 years (range 3 to 66). Pediatr. Med., Ed. K. Hereditary cerebral cavernous angiomas: clinical andgenetic features in 57 French families. The defect in the gene causes a repeat of4 or more copies of a combination of the C, A and G DNA nucleotides (CAGrepeats) compared to only 3 repeats in the normal gene. It is thought that both function as tumor suppressor genes, andwhen they are damaged, they allow the development of hamartomas. J. Von Willebrand disease andpregnancy. Gale Encyl. Consultant, 41, 445-453. L., Mirlesse, V., & Brunelle, F., 1996). Chen, F. K., 1993; Sonigo, P., Simole, L. (1999). References Berkow, R., Beers, M. Prenatal screening for Huntington's disease can be performed withouttesting whether the mother carries the gene or not. A., Lermont, L., Delezoide, A. The mean age for clinical onsetfound in this study was 32.6 years (range 5 to 74) in patients whose firstsymptom was seizures. Thedisorder affects both sexes, and symptoms appear in infancy or earlychildhood (The Complete Dictionary, 2 ). H., & Fletcher, A. Tumorsof the heart and brain were detected prenatally by ultrasound, andpostnatal echocardiography, spinal CT and MRI imaging, as well as typicalskin lesions in a study by Czechenski, Langille and Varady (2 ). Both males and females are affected. Thedisease is caused by a defect on chromosome 4 in the gene for a proteinknown as Huntington, whose function is currently unknown (Berkow, Beers andFletcher, 1997; Robinson, 1999). Itssize varies from 5 , daltons to 2 million daltons. (1996). The sex ratio was 23males and 18 females with hemorrhages, 31 male and 28 female withouthemorrhages. A.,Lermont, L., Delezoide, A. It occurs in approximately .5percent of the population and can cause seizures, hemorrhages and focalneurological deficits. In up to 5 percent of cases, the condition is inherited in anautosomal dominant manner, and studies have shown linkages to two loci onchromosome 7 and one on chromosome 3, known as the cerebral cavernousmalformation loci (CCM). K., 1993; Czechenski,J., Langille, E. Lancet, 354, 1183. The observed distribution of affected individuals in this study showedautosomal dominant inheritance in most families studied, with incompleteclinical penetrance of familial cerebral cavernosa and complete or almostcomplete penetrance of the disease using neuroimaging. An infant with rhabyomyomaprenatally diagnosed in a mother with tuberous sclerosis. (1998). De Bellis, D. It=s prevalence is estimated to be .5 percentto one percent. Sonigo, P., Simole, L. (1993). Pediatr. Tuberous sclerosis is characterized by hamartomasand involves multiple organ systems (O'Callaghan, 1999; Jalou, Hutcheon andSanz, 2 1). This variable expressivity means affected family membersmay have different levels of severity of bleeding, depending on whetherthey are heterozygous or homozygous for the disorder. (2 1). L., & Varady, E., 2 ; Sonigo, P., Simole, L. The Von Willebrand factor is a large, multimeric glycoprotein encodedon chromosome 12 (Saif and Allegra, 2 1). It is synthesized in endothelialcells and megakaryocytes, and circulates as a series of multimers. L., Mirtesse,V., & Brunelle, F. P., &Chu, K. Med., 155, 89-91. K. The symptoms are notusually evident at birth, although the can occur in infancy, but prenatalgenetic screening can identify affected offspring (De Bellis, 1999). The symptoms of Von Willebrand disease may occur at any age because ofits variable expressivity and wide variation in bleeding severity (Saif andAllegra, 2 1). (2 1). Merck Manual ofMedical Information. Pathol., 26, 1-4. & Adolesc. P., & Chu, K. Estimates of its prevalence for the United Kingdom are 3.7per 1 , but may be as high as 8 to 9 per 1 , (O'Callaghan).Linkage studies have shown loci on 9q34 (TSCI) and 16p13 (TSC2). Tuberous sclerosis.Arch. These extra CAGrepeats cause Huntington protein to contain an extra section which isthought to interact with other proteins in brain cells where it occurs, andcause cell death. (1999). Formosa Med.Assoc., 2, 185-187. A case report of antenataldiagnosis by ultrasonography. Czechenski, J., Langille, E. (1999). Genetic linkage analysis in 36 families showed astrong association with CCM1 on chromosome 7q in 65 percent of individuals. Patientshomozygous or doubly heterozygous for the disorder (two percent to 1 percent) have the most severe form of the disease and have low levels offactor VIII and low levels of Von Willebrand factor, while those who areheterozygous for the disorder have a milder form of the bleeding problems. Whitehouse Station, NJ: Merck Research Laboratories. J. Offspring inherit one set of chromosomes from the mother and onefrom the father. Huntington's disease affects both males and females (Robinson, 1999).In the United States, approximately 3 , people have the disease, andanother 15 , are at risk for developing it. (1997). Another dominantly inherited genetic disorder is cavernous angioma, aphakomatosis disease in which vascular malformations in the central nervoussystem consisting of enlarged capillary cavities with no intervening braintissue occur (Sonigo, P., Simole, L. 1, 1489-1492. Robinson, R. L.,Mirtesse, V., & Brunelle, F., 1996; Labauge, Laberge, Brunereau, Levy andTournier-Lasserve, 1998; Senior, 1999). Because it affects both sexes, women may be at riskduring delivery or the postpartum period, as well as throughout theirchildbearing years. Prenatal MRI diagnosis of fetal cerebraltuberous sclerosis. Intracardiactumor and brain lesions in tuberous sclerosis. Tuberous sclerosis. Jalou, H., Hutcheon, R. O'Callaghan, F. Von Willebrand disease is the most common inherited bleeding disorder,and is transmitted in an autosomal dominant manner with variable penetrance(Saif and Allegra, 2 1). Med, Ed.1 3 48. A., Lermont, L., Delezoide, A. The linkage testexamines the pattern of DNA near the gene in both the parent and the fetuswithout actually analyzing the repeats themselves. The onset of Huntington'susually occurs between the ages of 3 and 5 , but in 1 percent of casesthe onset is in late childhood or early adolescence. Untilnow, the major sign detected prenatally has been cardiac tumors(rhabydomyomas) which can be detected by echocardiography (Chen, F. Symptoms can be present at birth, and can also be detectedprenatally by ultrasonography (Chen, F. Senior, K. Amatch between parent and fetus suggests the fetus and the parent have thesame genetic makeup, but does not actually indicate whether either of themactually has the defective gene. A parent withsuch a gene has a 5 percent chance of passing it on to their offspring.One example of a dominantly inherited disease is Huntington's disease. W., & Allegra, C. Genetic basis for hereditary cavernous angiomasfound. In patients with nofamily history of the disease, there is a high percentage of spontaneousmutations leading to the new cases. TSCIencodes a protein known as tuberin, and TSC2 encodes a protein known ashamartin. P., & Chu, K. (2 ). Acta Radiol., 41, 371-374. Dominantly inherited genetic disorders are those in whichonly one copy of the gene for that disease is needed for the disease to bepresent (Robinson, 1999). BMJ, 318, 1 19-1 21. Huntington=s disease. Three point mutations havebeen identified in 12 subjects which cause stop codons: five weredeletions, two were insertions that caused frameshifts, and two were DNAdeletions resulting in abnormal splicing, all of which truncated KR1T1(Senior, 1999). (1996). G., & Sanz, A. CCM1 encodes for a 529 amino acid protein, KR1T1, which interacts withRAP1A, a member of the RAS family of GTPases.
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