DLA 13 Flashcards
Describe the characteristics of X-linked recessive disorders?
skipping of generations
NO male to male transmission
found in males more often
Duchenne Muscular Dystrophy (DMD)
tends to be lethal before the age of 30
enlarged calves and wasting of thigh muscles
Do not have children
X-linked recessive disorder
Becker muscular dystrophy
Same mutation found in DMD
Becker is a less severe mutation compared to duchenne
for example, BMD can have children
Hemophilia A
inherited deficiency of the clotting factor VIII, thus there is an increased tendency to bleed after minor traumas.
is caused by incorrect splicing
does show allelic heterogeneity
X-linked SCID
Caused by a defective gamma chain of the receptor for several different interleukins
T-cells are not able to mature, thus no immune function
SCIDX1 gene mutation
Manifestations in a female typically are due to?
skewed or asymmetric X-inactivation
Red/green color deficiency?
An example of a non-lethal sex-linked trait
Example of an X dominant disorder?
Rett syndrome
affects females more than males
however, males with this mutation normally die during pregnancy or right after birth
Incontinentia pigmenti?
An x-linked dominant disorder that is lethal to males
Males usually die in utero
variable expresstivity in females due to X-inactivation
Symtpoms of Incontinentia pigmenti?
rashes and blisters early in life
hyperpigmentation
intellectual disability
retinal detachment (in some)
More examples of X-linked dominant disorders?
- vitamin D resistant rickets
- rett syndrome (lethal in males)
- incontinentia pigmenti (lethal in males)
What is incomplete penetrance?
When an individual has an allele for a certain illness but does not show symptoms
What is full penetrance?
All those that have the mutated allele will show symptoms of that disorder
What is a general example of incomplete penetrance?
age-dependent penetrance
delayed onset
some people are heavily impacted and some are mildly impacted by a mutated allele why?
- random chance
- other genetic factors (sex)
- environmental factors
Example of variable expression?
hemochromatosis
males are more impacted than females due to gender.
males are not able to remove iron while females can
What is the meaning of pleiotropy?
This is a disorder where more than one organ system is impacted
Ex: marfan syndrome and osteogenesis imperfecta
What is locus heterogeneity?
mutations at different loci that cause the same disease
mutations of different genes that cause the same disease
Example of locus heterogeneity?
osteogenesis imperfecta - mutation at gene 17 or 7?
Explain breast cancer susceptibility genes?
BRCA1 and BRCA2
both of these genes are located at different chromosomes but they have a similar phenotype
Does charcot-Marie-Tooth disease show locus heterogeneity?
Yes, multiple genes are known that can lead to this disorder
Locus heterogeneity VS allelic heterogeneity
Locus = mutations of different genes that lead to the same disease state
Allelic = different mutations on the SAME gene
