Chapter 7 Genetic and Developmental Diseases

Review of Structure and Function Fertilization is the uniting of a sperm and ovum resulting in 23 pairs of chromosomes Diseases can result from abnormalities in the make-up of the 23 pairs Abnormalities may be caused by duplication or deletion of parts of a chromosome

Review of Structure and Function Every genetic trait is influenced by two alleles One allele may either be dominant or recessive –A dominant allele results in how the genetic trait is expressed –A recessive allele trait will only be expressed if both are defective

Review of Structure and Function Genotype –The genetic makeup of individuals –Even though this describes exactly what genes an individual has, it cannot predict how genes are expressed Non-penetrance Variable expressivity

Review of Structure and Function Phenotype –The physical and functional manifestation of genetic traits –In other words, the end result after taking into account non-penetrance and variable expressivity

Definitions Genetic disease –Caused by an abnormal gene, these are not necessarily familial Chromosomal disease –Microscopically visible structural changes in chromosomes

Definitions Familial disease –Several family members have the same genetic or chromosome based disease

Frequency and Significance of Developmental Abnormalities Monogenetic disease –Classified by whether the abnormal gene is located on an autosome or sex chromosome, and whether it is dominant or recessive –Autosomal disease is much more common than sex-linked disease

Frequency and Significance of Developmental Abnormalities Dominant disorders –The presence of the disease identifies those with the gene –Offspring has a 50% chance of inheriting the defective gene

Frequency and Significance of Developmental Abnormalities Recessive disorders –These appear sporadically –Offspring has a 25% chance of inheriting the defective gene—because they must inherit one defective gene from each parent

Frequency and Significance of Developmental Abnormalities Sex-linked recessive disorders –Appear in every other generation –Females with the abnormal gene on the “x” chromosome will not express signs of disease, because they have one normal “x” –However, males will express signs of disease, because they only have one “x”

Frequency and Significance of Developmental Abnormalities Inborn errors of metabolism –Enzyme defects that effect the metabolism of carbohydrates, proteins, lipids, or minerals. Mitochondrial disease –Affects the energy-producing apparatus –Can result in deficiencies of the brain, muscles and nerves

Frequency and Significance of Developmental Abnormalities Environmental Factors –Teratogens Known toxins or infectious agents that cause defects in the developing embryo or fetus an agent that interrupts or alters the normal development of a fetus, with results that are evident at birth, e.g. a chemical, virus, or ionizing radiation

Frequency and Significance of Developmental Abnormalities Environmental Factors –TORCH Diseases that cause mild disease in the mother, but devastating disease in the newborn Toxoplasmosis, Other (usually syphilis), Rubella, Cytomegalovirus, and Herpes simplex virus

Frequency and Significance of Developmental Abnormalities Embryonic Anomalies –Congenital heart defects are the most common –Abnormalities of the kidney and urinary tract

Frequency and Significance of Developmental Abnormalities Fetal Diseases –Erythroblastosis fetalis –Chorioamnionitis –Nutritional deficiencies in the mother, affect the growth and development of the fetus

Frequency and Significance of Developmental Abnormalities Perinatal disease –Prematurity

Frequency and Significance of Developmental Abnormalities Most common diseases of infancy –Congenital and chromosome abnormalities –Prematurity and low birth weight –Sudden Infant Death Syndrome –Complications of maternal illness –Diseases of the placenta, cord, and membranes

Symptoms, Signs, and Tests Genetic disease –This will be highly individualized depending on where the defect is located –Some diseases will present at birth, while others will not present until later

Symptoms, Signs, and Tests Genetic disease –Laboratory studies or genetic testing can be diagnostic –Some diseases can be diagnosed before birth, while others are tested for at birth, thus providing early treatment to minimize complications

Symptoms, Signs, and Tests Chromosomal disease –Often suspected by physical exam –Karyotyping provides accurate diagnosis and counseling Embryonic anomalies and fetal diseases –The method of diagnosis depends on the nature of the disease

Specific Diseases Genetic disease –Often have a racial predilection Sickle Cell Anemia—African or Mediterranean Cystic Fibrosis—northern European

Specific Diseases Chromosomal Disease –Caused by increases or decreases in the normal complement of chromosomes or changes to parts of one or more arms of chromosomes Down syndrome Klinefelter syndrome Turner syndrome Fragile X syndrome