TAILIEUCHUNG - Chapter 062. Principles of Human Genetics (Part 19)

Penetrance refers to the proportion of individuals with a mutant genotype that express the phenotype. If all carriers of a mutant express the phenotype, penetrance is complete, whereas it is said to be incomplete or reduced if some individuals do not have any features of the phenotype. Dominant conditions with incomplete penetrance are characterized by skipping of generations with unaffected carriers transmitting the mutant gene. For example, hypertrophic obstructive cardiomyopathy (HCM) caused by mutations in the myosin-binding protein C gene is a dominant disorder with clinical features in only a subset of patients who carry the mutation (Chap. 231) | Chapter 062. Principles of Human Genetics Part 19 Penetrance refers to the proportion of individuals with a mutant genotype that express the phenotype. If all carriers of a mutant express the phenotype penetrance is complete whereas it is said to be incomplete or reduced if some individuals do not have any features of the phenotype. Dominant conditions with incomplete penetrance are characterized by skipping of generations with unaffected carriers transmitting the mutant gene. For example hypertrophic obstructive cardiomyopathy HCM caused by mutations in the myosin-binding protein C gene is a dominant disorder with clinical features in only a subset of patients who carry the mutation Chap. 231 . Patients who have the mutation but no evidence of the disease can still transmit the disorder to subsequent generations. In many conditions with postnatal onset the proportion of gene carriers who are affected varies with age. Thus when describing penetrance one has to specify age. For example for disorders such as Huntington disease or familial amyotrophic lateral sclerosis which present late in life the rate of penetrance is influenced by the age at which the clinical assessment is performed. Imprinting can also modify the penetrance of a disease see below . For example in patients with Albright hereditary osteodystrophy mutations in the Gsa subunit GNAS1 gene are expressed clinically only in individuals who inherit the mutation from their mother Chap. 347 . Sex-Influenced Phenotypes Certain mutations affect males and females quite differently. In some instances this is because the gene resides on the X or Y sex chromosomes X-linked disorders and Y-linked disorders . As a result the phenotype of mutated X-linked genes will be expressed fully in males but variably in heterozygous females depending on the degree of X-inactivation and the function of the gene. For example most heterozygous female carriers of factor VIII deficiency hemophilia A are asymptomatic because .

• Y học thường thức
• Principles of Human Genetics
• bệnh học và điều trị
• bài giảng bệnh học
• tài liệu y khoa
• Harrisons Internal Medicine
• Biological information
• Lecture Genetics
• Human genetics
• Modern genetic techniques
• Mendels principles
• Mendels principles of heredity