Ch07 genetic & congenital disorders

Ch07 genetic & congenital disorders - CHAPTER Genetic...

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GENETIC AND CHROMOSOMAL DISORDERS Single-Gene Disorders Autosomal Dominant Disorders Autosomal Recessive Disorders X-Linked Disorders Mitochondrial Gene Disorders Multifactorial Inheritance Disorders Chromosomal Disorders Alterations in Chromosome Duplication Alterations in Chromosome Number Alterations in Chromosome Structure DISORDERS DUE TO ENVIRONMENTAL INFLUENCES Period of Vulnerability Teratogenic Agents Radiation Chemicals and Drugs Infectious Agents DIAGNOSIS AND COUNSELING Genetic Assessment Prenatal Diagnosis Maternal Serum Markers Ultrasound Amniocentesis Chorionic Villus Sampling Percutaneous Umbilical Blood Sampling Fetal Biopsy Cytogenetic and Biochemical Analyses G enetic and congenital defects are important at all levels of health care because they affect all age groups and can involve almost any of the body tissues and organs. Congenital defects, sometimes called birth defects, develop during prenatal life and are present at birth, athough some, such as cardiac abnormalities, may not be- come apparent until some years later. The term congenital does not imply or exclude genetic disorders, which are usu- ally hereditary in origin. Birth defects, which affect more than 150,000 infants each year, are the leading cause of infant death. 1 Birth de- fects may be caused by genetic factors ( i.e., single-gene or 135 CHAPTER 7 Genetic and Congenital Disorders multifactorial inheritance or chromosomal aberrations), or they may be caused by environmental factors that occurred during embryonic or fetal development ( i.e., maternal dis- ease, infections, or drugs taken during pregnancy). In rare cases, congenital defects may be the result of intrauterine factors such as fetal crowding, positioning, or entangle- ment of fetal parts with the amnion. This chapter provides an overview of genetic and congenital disorders and is di- vided into three parts: (1) genetic and chromosomal dis- orders, (2) disorders caused by environmental agents, and (3) diagnosis and counseling. Genetic and Chromosomal Disorders After you have completed this section of the chapter, you should be able to meet the following objectives: DeFne the terms congenital, allele, gene locus, gene mutation, genotype, phenotype, homozygous, heterozygous, polymorphism, gene penetrance, and gene expression Describe three types of single-gene disorders Differentiate between mitochondrial and nuclear genes Contrast disorders due to multifactorial inheritance with those caused by single-gene inheritance Describe two chromosomal abnormalities that demonstrate aneuploidy Describe three patterns of chromosomal breakage and rearrangement Relate maternal age and occurrence of Down syndrome Genetic disorders can be described as a discrete event that affects gene expression in a group of cells related to each other by gene linkage. Most genetic disorders are caused by an alteration in DNA sequences that alter the synthesis of a single-gene product. However, some genetic disorders are caused by chromosome rearrangements that
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Ch07 genetic & congenital disorders - CHAPTER Genetic...

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