Chapter 5 Genetic and Congenital Disorders Flashcards
Alleles
The two members of a gene pair, one inherited from the mother and the other from the father.
Homozygous
The alleles for a gene pair are identical
Heterozygous
The alleles for a gene pair are different
Genotype
The genetic composition of a person. The person has xx.
Phenotype
The observable expression of a genotype.
What are Single-Gene Disorders?
How are they passed on?
Mutation or defectiveness of a single allele at a single gene locus.
Single-Gene disorders are passed on in the standard mendelian pattern. Depends on if the single gene is dominant or recessive.
Autosomal VS sex chromosome
Autosomal - one of the 22 numbered chromosome pairs of genomes.
Sex - sex chromosome
Autosomal dominant disorders
- Examples -
Single mutant gene from affected parents is passed to offspring regardless of sex. 50% chance of the affected parent passing the gene on to each child.
Examples:
- Marfan Syndrome
- Polydactyl
- Neurofibromatosis
Marfan Syndrome
1. Type of inheritance
2. What is affected?
3. Common abnormalities
- Marfan Syndrome is an autosomal dominant inheritance disorder. Meaning the affected parent has a 50% to pass the disease to each child.
- The disorder targets connective tissue. The organs most commonly affected are the eyes, skeleton, heart, spine.
- Hypermobility of joints. Long limbs. Long torso. Predisposition to lens dislocation and myopia due to weakness of associated muscles. Kyphosis and scoliosis. Chest abnormalities. Cardiac issues including mitral valve prolapse, degeneration of the aortic valve ring, and development of aneurysms and dissections.
Age of discovery Autosomal dominant VS autosomal recessive
AD is found later in life
AR is found earlier in life.
Autosomal Recessive Disorders
1. More commonly seen in?
2. Chances of occurrence?
3. Examples
Occur only when both genes in a pair are affected by the mutation. Can affect both males and females.
1. More commonly seen with inbreeding due to the increased likelihood of both parents having the mutation.
2. 25% chance of affected. 50% of carrier. 25% chance of unaffected.
3. Tay-Sachs and PKU
Tay-Sachs Disease
1. Inheritance
2. What is affected?
3. Manifestations/ Course
- An autosomal recessive trait disease
- Accumulations of GM2 in the lysosomes occur in all tissues but are most prominent in the retina and the neurons. These accumulations build until cell destruction is seen.
- The infant appears normal but around 6-12 months of age, the accumulations start to cause damage to the neurons and retina. Progressive muscle weakness, flaccidity, decreased motor and mental function. Rapid progression leads to seizures and death within 4-5 years of age.
X-linked recessive
A disease that affects the sex chromosomes. The X chromosome is almost always the one affected.
The typical spread of X linked recessive genes occurs through the carrier father transmitting his mutated X to his daughters since he only has the mutated X to give. His sons are not affected since the Y is normal.
Fragile X-Syndrome
1. Inheritance
2. Manifestations
1.An X-linked dominant disorder. Affects males twice as much as females.
2. Cognitive issues. Physical traits of long face, large mandible, everted ears (ears that stick out)
Multifactorial inheritance VS single-gene inheritance
Multifactorial disorders do not follow a clear set of inheritance pattern. Can be expressed early or later in life.
X linked recessive
Males VS Females
Males are more likely to display the disorder
Females are more likely to be carriers
Down Syndrome
1. Type of inheritance
Trisomy 21 - 3 chromosomes on 21.
Turner Syndrome
1. Type of inheritance
2. Features
Monosomy X - only one X is displayed on the genes.
Short statue, webbed neck, splayed arms, lymphedema of legs,
Klinefelter Syndrome
1. Inheritance
2. Features
Polysomy X - additional X chromosome.
2. Female like features - gynecomastia, short statue, decreased pubic hair, small testes, narrow shoulders.
Mitochondrial DNA
Passed down maternally. They have their own DNA.
Period of vulnerability
- What is this?
- When is this period?
- What is going on?
Period of time where an embryo’s development is at greatest risk of being disturbed.
From day 15 to day 60 after conception. First 8 weeks.
This is the period of time corresponds with the development of organs.
Teratogenic agents
Produce abnormalities during embryonic development.
- Radiation
- Chemicals and drugs (alcohol, cocaine, folic acid deficiency)
- Infectious agents
Alcohol as a teratogenic
- How does it differ from other teratogenic agents
- Manifestations
Alcohol freely passes through the placenta barrier exposing the fetus to the same alcohol levels as the mother.
- Can cause adverse effects throughout the pregnancy, not just during the period of vulnerability.
- CNS changes, developmental delays, behavior issues, skull and brain changes, small palpebral fissures (eye openings), thin vermillion border (upper lip), elongated, flattened midface, smooth philtrum (space under nose).
Folic Acid deficiency
Associated with neurotubal defects (spina bifida, anencephaly) .
All women of childbearing age are recommended to take 400 u per day.
TORCH
Commonly implicated microorganisms associated with fetal abnormalities.
T - toxoplasmosis
O - other
R - Rubella (German measles)
C - cytomegalovirus
H - herpes
What are some methods of genetic or fetal assessment?
- Ultrasound
- Serum markers
- Amniocentesis
- Chorionic Villus sampling
- Umbilical cord blood sampling
