chapter 7 genetic and developmental diseases. review of structure and function fertilization is the...
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Chapter 7Genetic and
Developmental Diseases
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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
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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
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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
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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
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Definitions
• Genetic disease– Caused by an abnormal gene, these are not
necessarily familial
• Chromosomal disease– Microscopically visible structural changes in
chromosomes
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Definitions
• Familial disease– Several family members have the same
genetic or chromosome based disease
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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
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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
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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
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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”
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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
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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
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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
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Frequency and Significance of Developmental Abnormalities
• Embryonic Anomalies– Congenital heart defects are the most
common– Abnormalities of the kidney and urinary
tract
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Frequency and Significance of Developmental Abnormalities
• Fetal Diseases– Erythroblastosis fetalis– Chorioamnionitis – Nutritional deficiencies in the mother, affect
the growth and development of the fetus
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Frequency and Significance of Developmental Abnormalities
• Perinatal disease– Prematurity
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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
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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
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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
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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
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Specific Diseases
• Genetic disease– Often have a racial predilection
• Sickle Cell Anemia—African or Mediterranean
• Cystic Fibrosis—northern European
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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