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KCSU17 Genetics > Sex linked disorders > Flashcards

Sex linked disorders Flashcards

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1
Q

inheritance of genes located on sex chromosomes

A

sex linked inheritance

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2
Q

males and sex chromosomes

A

receive their only X from mom

x-linked mutation will be present in any male with disease

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3
Q

females and sex chromosomes

A

X chromosomes from both parents

may not express the disease if mutation exists (x inactivation)

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4
Q

x linked recessive

A

phenotype is not expressed in females, exclusively men

all daughters of affected males are carriers

no male to male transmission

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5
Q

x linked dominant

A

phenotype is consistently expressed in female

females > males

all daughters of affected males are affected but not sons

Men usually die in uterine

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6
Q

y linked

A

affects only males

affected males always have affected fathers

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7
Q

x linked recessive probability

A

affected men born from carrier mothers have 50% risk of disease

no male to male transmission

affected male can only pass disease onto daughter (she will be a carrier)

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8
Q

x linked dominant probability

A

child of an affected female has 50% risk of disease

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9
Q

y linked transmission

A

affected dad CANNOT give to his daughter

affected dad CAN give to his son

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10
Q

mitochondrial traits transmission

A

appear in every generation

can affect males and females

fathers do not pass mitochondrial traits, only ovum contributes mitochondria to offspring

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11
Q

x inactivation

A

ability of second X chromosome to compensate for a mutant or defective gene on other X chromosome

occurs in every female, during development. Randomly, so that females are essentially mosaics

incomplete, so some regions remain active in all copies

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12
Q

x chromosome

A

X is much larger than Y so it codes for many proteins

females have twice the dosage of X than males

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13
Q

calico cats

A

example of X inactivation
alternating black and orange spots show the mosaicism in female cats

one contains X with active orange allele and one with black allele

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14
Q

X linked recessive disorders discussed in this class

A

hemophilia
Duchenne muscular dystrophy
Becker muscular dystrophy

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15
Q

hemophilia A and B are distinguished by

A

aPTT test

tests intrinsic pathway, both will have elevated aPTT

factor 8 and 9, involved in intrinsic pathway, are elevated

other than this test, hemophilia A and B are indistinguishable

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16
Q

hemophilia

A

sex linked recessive

severe bleeding disorder

85% are A and 15% are B

aPTT test distinguishes

prolonged or severe bleeding from wounds and hemorrhage in joints and muscles causes hemearthroses and intracranial disorder

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17
Q

genetic abnormality:

hemophilia A

A

long arm q of X chromosome (F8C gene)

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18
Q

protein affected:

hemophilia A

A

deficiency or defect in factor 8

clotting factor, therefore causes excessive bleeding

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19
Q

treatment for hemophilia A and B

A
  1. monoclonal purified, plasma derived factor VIII (can cause infection)
  2. recombinant Factor VIII (non human, made in lab so safer)
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20
Q

hemophilia B

A

aka christmas disease

caused by mutation on F9 of X, coding for Factor 9 Leyden

severe hemophilia during childhood, spontaneous resolution during puberty

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21
Q

most common and most severe form of muscular dystrophy

A

Duchenne muscular dystrophy

characterized by progressive weakness and loss of muscle

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22
Q

genetic abnormality

Duchenne muscular dystrophy

A

Xp21

deletion or duplication producing FRAMESHIFT mutation

more common in males

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23
Q

Duchenne muscular dystrophy

protein affected

A

dystrophin

results in ABSENCE of protein, most likely responsible for maintaining structural integrity of cytoskeleton

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24
Q

Duchenne muscular dystrophy

pathophysiology

A

lack of dystrophin causes muscle cells to die as they are stressed by muscular contractions

muscle death causes release of creation kinase, CK, into the blood stream

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25
Duchenne muscular dystrophy | clinical manifestations
progressive weakness and loss of muscle cardiomyopathy in all affected after 18, few live beyond 30 respiratory problems and DMC as MC cause of death proximal weakness, waddling gait, difficulty climbing pseudo hypertrophy of calves
26
Duchenne muscular dystrophy | expression pattern
symptoms seen before age 5 female heterozygote carriers often show some symptoms DMD is rapidly progressive, children in wheel chair by age 12 Gowers maneuver to ID
27
Duchenne muscular dystrophy | treatment
mandage cardiomyopathy | prednisone to improve strength, function
28
Becker muscular dystrophy | genetic abnormality
Xp21, dystrophin gene IN-FRAME mutation
29
Becker muscular dystrophy | protein affected
dystrophin DECREASED LEVELS 10% from spontaneous mutation
30
Becker muscular dystrophy | clinical manifestations
slower progression, less severe than DMD never lose ability to walk later onset skeletal muscle weakness DMC is MC cause of mortality
31
Becker muscular dystrophy | expression pattern
11 years of age
32
most common inherited cause od mental retardation
Fragile X syndrome only need one mutation to cause disease (both males and females) MORE MEN
33
Fragile X syndrome | genetic abnormality
FMR1 gene, Xq28 expansion of CGG repeat
34
Fragile X syndrome | penetrance levels
normal CGG length is 6-54 normal, transmitting males = 60-200 affected individuals = 200-thousands of CGGs anticipation is seen with Fragile X (# increases w/generation and severity)
35
anticipation Fragile X syndrome in men
permutation is passed thru men then it doesn't significantly increase in size dad can give to daughter, not son
36
anticipation Fragile X syndrome in women
CGG expansion is unstable, high risk of it expanding to full mutation in children mom can give to daughter (50%) and son as well
37
Fragile X syndrome | protein affected
FMRP or FMR-1 protein is necessary for normal brain development and function
38
Fragile X syndrome | pathophys
when repeats expand over 200, the gene is turned off = full mutation this causes decrease in protein product which causes manifestations
39
Fragile X syndrome | clinical manifestations
distance facial appearance (lg. head, long face, lg. ears, macroorchidism) moderate to severe mental retardation physical features distinct after puberty normal life expectancy
40
Fragile X syndrome | expression pattern
depends on number of repeats females there is variability in phenotype expression due to effect of x-inactivation
41
Fragile X syndrome | penetrance
reduced pentrance
42
Rhett syndrome
x-linked dominant disorder of brain development occurs exclusively in females
43
rhett syndrome | genetic abnormality
MECP2 gene on X chromosome (Xq28)
44
Rhett syndrome | protein affected
MECP2 regulates other genes in brain by switching them off binds a MeCP2 protein to methylated cells to prevent access to DNA transcriptions
45
Rhett syndrome | pathophys
MECP2 mutations disrupt normal functioning of nerve cells | normal brain development until 6-18 months
46
why do symptoms of Rhett syndrome not appear until 6-18 months?
by 6 months new neuronal cells are maturing and certain proteins become active and MeCP2 must interact with them to promote new and existing brain cell development
47
Rhett syndrome | clinical manifestations
disruption of neurotransmitters causes excessive anxiety (withdrawn and anxious) autistic like behaviors, acquire specific symptoms like teeth grinding and hand wringing
48
MECP2 and anxiety
normally controls activity of CRH this mutations results in overabundance of CRH in brain therefore Rhett syndrome results in excessive anxiety and stress
49
Rhett syndrome | expression pattern
x-inactivation 50% of mutant gene and 50% of normal gene causes Rhett to develop (50:50) if majority of x cells turn off chromosome that includes mutant MECP2 gene then mild disorders develop and patients don't show the pattern
50
Rhett syndrome | penetrance pattern
not all children with MECP2 mutations will develop classic Rhett syndrome
51
Rhett syndrome treatment
gene therapy is being developed
52
x-linked dominant disorders discussed in this class
Rhett syndrome | Fragile X syndrome
53
Y-linked disorders genetic transmission
dad cannot give it to his daughter but CAN give to his son
54
y chromosome
plays a crucial house keeping role into cell referred to as pseudoautosomal
55
Y-linked genes
SRY gene - specifies male fathers and maleness hypertrichosis pinnae auris -- hairy ears, gene found on Y chromosome
56
Mitochondrial disorders
appear in every generation of a family affect both males and females fathers DO NOT pass mitochondrial traits to children, only mothers
57
mitochondria
have their own DNA found in tale of sperm, falls off when fertilization occurs therefore only ovum contributes to mitochondria in offspring
58
heteroplasmy
fraction of molecule in mtDNA that carry a mutation phenotype of a cell depends on percentage of mutated DNA it contains severity of condition correlates with extent of heteroplasmy
59
mitochondrial disorders in this class
Leber Hereditary Optic Neuropathy (LHON) Myoclonic Epilepsy with Ragged Red Fiber Syndrome (MERRF) Pearson Syndrome
60
LHON
bilateral loss of central vision caused by atrophy of optic never vision disappears within a few weeks appears in second or third decade of life and affects more men than women (classic)`
61
Myoclonic Epilepsy with Ragged Red Fiber Syndrome
MERRF characterized by myoclonic epilepsy generalized convulsions of myopathy with presence of ragged red fibers clumps of diseased mitochondria that accumulate and aggregate in individual muscle fivers
62
LHON is caused by mutations
mtDNA component of the elevon transport chain specific inability to generate ATP
63
MERRF is caused by mutations
mtDNA caused by mutations of mitochondrial tRNA (tRNALys) caused by a general defect in mitochondrial protein synthesis
64
Pearson Syndrome
first year of life children usually die before three years of life affects hematopoiesis and endocrine pancreatic function anemia with vacuolization of bone marrow precursors, manifested with microcytic anemia, thrombocytopenia, neutropenia
65
mitochondrial genomes reading assignment
mitochondria contain multiple genomes, every cell contains multiple mitochondria req. for energy production vary from one tissue to another mutations in mitochondrial DNA affect only a fraction of mitochondrial genomes within a given individual

KCSU17 Genetics (14 decks)

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