Chapter 6 -Genetics Flashcards
Define the terms genetic disorder, birth defect, genotype, and phenotype.
Genetic disorder is the discrete event that affects gene expression in a group of cells related to each other by gene linkage
Birth Defect are abnormalities of a body structure, function, or metabolism that are present at birth
Genotype is the genetic composition
Phenotype is the observable expression of genotype
Explain the differences between autosomal dominant and autosomal recessive disorders.
Autosomal Dominant
-Each child has a 50% chance of inheriting the disorder
Only need to get the abnormal gene from one parent
Autosomal Recessive
- Each child has a 25% change of being affected, 25% chance of being unaffected, and 50% chance of being a carrier
- Need two copies of abnormal gene to be affected
Compare the characteristics of Marfan syndrome and Neurofibromatosis disorders.
MARFAN SYNDROME
Affects fibrillin I, a component of extracellular matrix, resulting in
decreased maintenance of tissue architecture of body structure
Skeletal
-Long thin body, fingers
-Hyperextensible joints
-Kyphosis, scoliosis
-Pectus excavatum (deeply depressed sternum)
–Pigeon chest
Ocular
-Bilateral dislocation of lens (weak ligaments)
-Myopia with predisposition to retinal detachment
Cardiovascular
- Mitral valve prolapse
- Progressive dilation of aortic valve ring
- Weak aorta and other arteries (dissection, rupture)
- -Increased risk of dissection and wall separates and weakens
- Increased risk of dissection during pregnancy
NEUROFIBROMATOSIS DISORDERS
-Neurogenic tumors arising from Schwann cells in peripheral nervous system
Result of defect in tumor-suppressor gene
Type NF-1 (Recklinghausen disease)
Type NF-2
TYPE 1 Autosomal dominant (50% familial, 50% new mutation)
Manifestations -Neural tumors (neurofibromas) on body -Often erupt at puberty -Soft, pink lesions projecting from skin -Firm, round, can be painful Café au lait spots = birth marks -Flat, brown/light brown -Sharply demarcated edges -Lisch nodules on iris Often appear at 6 years of age Often no problem Scoliosis Learning difficulties Epilepsy Vision problems
TYPE 2 -Acoustic nerve tumors -Multiple intracranial & spinal meningiomas near cranial nerve VIII --Auditory-vestibular nerve Asymptomatic for first 15 years
Manifestations
- Headaches, hearing loss, tinnitus
- Exacerbated by pregnancy and oral contraceptives
Discuss the differences between the autosomal recessive disorders phenylketonuria and Tay-Sachs disease
PKU
- Autosomal recessive disorder
- -Both parent must have gene
Elevation of phenylalanine
- -Amino acid obtained from diet
- -Usually converted to tyrosine by liver enzyme
- -Tyrosine assists neurotransmitter and melanin synthesis
MANIFESTATION
- symptoms appear in a few weeks but too late as CNS damage has occurred
- Musty odor to sweat/urine
- Light skin and hair, eczema
- Microcephaly, mental retardation, seizures
TREAMENT
Dietary restriction must begin when the child is invitro to prevent mental retardation….”diet for life”
Enzymes replacement being developed
TAY-SACHS DISEASE
- Rare autosomal recessive genetic disorder
- Eastern European Jew population (high carrier rate)
- Accumulation of lysosomes in all organs, mostly brain and retina neurons
- -Cherry-red spot on macula
- -Neuron destruction in cerebellum, basal ganglia, brain stem, spinal horn and ANS
MANIFESTATION
- Infant appear normal at birth
- Progressive weakness, muscle flaccidity appearing at approximately 6 months of age
- -Decreased attention span
- Rapid deterioration of motor and mental function, often with generalized seizures after approx. 10 months
- Visual impairment and eventual blindness
- Death by 4-5 years (no cure or treatment)
Discuss the etiology, manifestations, and usual treatment of the childhood disorders of cleft lip and cleft palate.
CAUSE
- Hereditary
- Environmental
- Teratogens (rubella, anticonvulsant medications)
- -Anticonvulsant medications
MANIFESTATION
- Vary (size, involvement of teeth, uni/bilateral)
- Cleft palate: difficulty feeding
- Difficulty vocalizing/speech
TREATMENT
- Plastic surgery
- -3 months to close lip
- -1 year to close palate
- Dental/Orthodontia work
- Speech therapy
Relate maternal age and occurrence of Down syndrome and manifestations
RISK FACTORS Increases with maternal age 1/25 births after 45 years of age Also a form of downs that has no relation to maternal age (5%) Environmental agents chemicals, radiation, drugs
MANIFESTATION
CNS
-Mental retardation
-Increased risk of alzheimer disease
Head/face -Small, square skull -Flat facial profile, small nose, depressed nasal bridge Eyes: slant upwards, epicanthal fold Ears: small, low-set malformed Tongue: large protruding (open mouth)
Skeletal -Retarded growth Hands: short, fingers curled inwards, single palmar crease (simian crease) -Large space between large & second toe -Hypotonia, joint laxity -Fat pad on back of neck CVS -Congenital heart defects GI malformations Acute Leukemia
Compare and contrast Turner syndrome and Klinefelter syndrome.
All or part of X chromosome is absent
MANIFESTATION Sexual -Lack ovaries (no menstruation) -Lack of secondary sex characteristic CNS -Visual/spatial disorganization --Difficult driving, doing math, psychomotor skills, focusing --strabismus
Skeletal
-Short, with normal body -proportion
-Deformed nail growth; short 4th metacarpal
CVS
-Congenital heart defects (coarctation of aorta, aortic valve deformities)
-Altered vascular supply to kidney (displacement)
Integument
-Neck webbing
-Multiple pigmented nevi
-Lymphedema of hands/feet
KLINEFELTER SYNDROME -At least one extra X chromosome in male (XXY) -Often undetected at birth except for Small penis Small, firm testicle
MANIFESTATION
- Gynecomastia
- Sparse facial and body hair
- Small testes (don’t respond at puberty to androgens)
- Inability to produce sperm
- Tall stature at puberty d/t low testosterone levels (lower body longer than upper)
- Female distribution of fat later in life
Discuss the general factors and teratogenic agents that can impact embryonic and fetal development.
General Maternal Factors
- Hormonal balance
- State of health
- -Measles can cause malformations
- -DM
- Nutritional status
- Medications/drugs
Teratogenic Agents
-Producing abnormalities during embryonic or fetal development
State the cautions that should be observed when considering impact of chemicals and the use of drugs during pregnancy.
Mutagenic
Possibly effecting inheritable genetics
No evidence of diagnostic procedures being dangerous
Possible damage with diagnostic radioactive iodine during 13th week of gestation when thyroid gland developing
Microcephaly
Skeletal malformations
Mental retardation
Properties
-Cytotoxic, anti-metabolic, growth-inhibiting
Dependent upon
- Time of exposure (embryonic/fetal development)
- Length of exposure (time)
- Extent of exposure (dosage)
Type of chemical/drug
- -Lipid-soluable will cross placenta more easily
- -Small molecule weight cross more easily
Alcohol Smoking : low birth weight Mercury: defects, blindness Anticoagulants Anticonvulsants Anti-cancer agents Vitamin A Accutane Tetracycline Thalidomide
Describe the effects of alcohol abuse on fetal development and birth outcomes.
Alcohol is lipid-soluble, moderate molecular weight
- Passes freely across placental barrier
- Results in concentration just as high in fetus as in mother
Effected dependent on time/amount
Prenatal and/or postnatal growth retardation
CNS abnormalities
-Development and intellectual delays
Characteristic facial features
Growth deficits
Explain the possible fetal impact of a folic acid deficiency
Implicated in development of neural tube defects
- Anencephaly (no brain)
- Spina bifida
400ug/day recommended during pregnancy
Dietary sources
Cereal (enriched)
Orange juice
Dark, leafy green veg/legumes
Define TORCH, and discuss its importance in regards to congenital malformations.
Toxoplasmosis
- Parasitic infection from raw/poorly cooked meat, domestic cat feces resulting in CNS symptoms
- Mother to fetus transmission
Rubella (german measles)
- Remains endemic in some developing countries
- Mother infected in first 20 weeks of pregnancy = defects
Cytomegalovirus
-Can lead to retardation
Herpes simplex virus type 2
