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