Recessive Diseases Flashcards
What is mode of inheritance for DMD?
X-linked recessive
What kinase is elevated in DMD?
serum creatine kianse
What is most common cause of death for DMD?
cardiac or respiratory failure
Which disease can you not lift your head when lying and which an you lift it?
cannot lift: DMD can lift: BMD
Where is the mutation for DMD & BMD?
dystrophin
What is type of mutation for DMD
null mutation, deletions, frameshifts, nonsense - complete loss of fuction
no dystrophin
What is type of mutation for BMD?
in frame deletion
partially functional dystrophin
Where are the deletions in dystrophon in BMD less severe?
in middle of dystrophin protein
Do DMD pts reproduce?
No
Do BMD pts reproduce?
yes
If exon length is not a multiple fo three which MD is it?
DMD
If exon length is a multiple of 3 what MD is it?
BMD
What is a way to stop DMD from happening genetically?
have it Read through the stop codons
Inborn error of metabolism means what?
disorder caused by deficiency of enzymes involved in metabolic pathways
What is an enzymopathy?
general term for disease caused by enzyme deficiency
What is mode of interitance for enzymopathies
almost always recessive
Why are enzymopathies recessive?
the one allele produces enough phenotype needed
How does pathology occur in enzymopahy?
disease occurs b/c of stubstrate accumulation and/or product deficiency
Phenylketonuria, alkaptonuria, albanism, homocysteinuria, maple syrup urine disease are alle xamples of what kind of disease
amino acid metablism disease, they are enzymopathies
what diseases occur due to mutation of Phe, Tyr metabolism pathway?
Phenylketonuria, alkaptonuria, albanism
Can we synthesize phenylalanine?
No, get it from diet from proteins
What aa does phenylalanine get turned into?
tyrosine
can we synthesize tyrosine?
yes
What important things is tyrosine used for?
tissue proteins, melanin, catecholamines, fumarate acetoacetate
Phenylalanine Hydroxylase (PAH) mutation is what disease?
Phenylketonuria (PKU)
enzyme: HGD is what disease?
alkaptonuria
What does PAH stand for?
Phenylalanine Hydroxylase
What does PKU stand for?
Phenylketonuria
PKU has elevated phenylalanine in the blood, what is the name of this?
hyperphenylalaninemia
What is main clinical presentation of PKU?
mental retardation
Mental retardation, musty odor, developmental delays, micrcephaly, hypopigmentation are symptoms of what disease?
PKU
Accumulating phenylalanine is converted to what in PKU
Phenylpyruvate and other ketoacids
What is the affect of the accumulation of phenylalanine that is converted to Phenylpyruvate and other ketoacids?
toxic effects
What is the treatment of PKU
dietary restriction of Phe (phenylalanine)
When does pt need to start PKU treatment?
within first month
When does pt need to start PKU treatment?
within first month
what disease helped initiate use of newborn screening
PKU
If pts with PKU has restricted diet in first month what is there IQ?
normal
If a pt has been on restricted diet and has normal IQ, what happens if they go on normal diet
It very slowly lowers their IQ, takes years to lower it
If a female with PKU becomes pregnant, what is it very important she do?
stick to restricted low Phe diet
What happens if embryo is exposed to high Phe even if they are heterozygous
the baby is affected b/c of the high exposure to Phe
What gene is affected in PKU?
PAH
Describe allelic heterogeneity in PKU
b/w different races there are different mutations on same gene that can cause PKU
What is hyperphenylalaninemia?
elevated phenylalanine in blood
Any mutation lead that leads to defeiciency of cofactor will also lead to what
hyperphenylalniniemia
what are the two ways you can end up with tetrahydrobiopterin?
two enzymes will block BH4 and lead to hyperphenylalninemaia
tyrosine hydroxylase
tryptophan hydroxylase
besides accumulation of phenylalanine, what happens in BH4 deficiency?
defieicency of neurotransmitters and serotonin
What are two ways to treat BH4 defieciency?
restricted diet
give them neurotransmitter precursers
What are the 5 genes that can lead to hyperphenylalaninemia?
PKU
2 genes in BH4 synthesis
2 genes involved in BH4 recyling
What is the name of the black urine disease?
alkaptonuria
where is the enzyme deficiency in alkaptonuria?
homogentisate 1,2-dioxygenase (HGD)
What does HGD stand for?
homogentisate 1,2-dioxygenase
What is HGD often referred to as?
homogentisic acid oxidase (HGO)
what is mode of inheritance for alkaptonuria?
AR
What accumulates in alkaptonuria?
Homogentisic Acid
What happens with accumulation of Homogentisic Acid?
it oxidizes, and the products accumulate in soft tissues
What is ochronosis
bluish-black discoloration of soft tissues
the damage to cartilage in alkaptonuria can cause what?
osteoarthritis
What can potentiall yhappen to heart in alkaptonuria?
calcification of aortic valve
What is mode of inheritance for oculocutaneous abinism?
AR
OCA1 is what?
oculocutaneous albinism
where is deficiency in OCA1?
tyroinase (TYR)
why does OCA1 cause lack of pigment in skin?
inabilityt o convert tyrosine to melanin
what are the two varients of OCA1?
OCA1A & OCA1B
which varient of OCA1 is most severe?
OCA1A
What is OCA1B?
oculocutaneous albinism, less severe, residual activity
What is OCA1A?
oculocutaneous albinism, the severe form, no pigmentation, easily burned, visual acuity defects
Where is defieiceny in homocystinuria?
cystathionine beta synthase
what does CBS stand for?
cystathionine Beta synthase
what is mode of inhertiance for homocystinuria?
AR
What cofactor does CBS need?
Pyridoxal phosphate
what does PLP stand for?
pyridoxal phosphate
What is clinical presentation of homocystinuria
intellectual disability seizures nearsightedness, lens dislocation osteoporosis musculoskeletal defomritions ( long bones, similar looking to marfan syndrome)
PLP is an active form of what?
VitB6 (a vitamin)
What is a way to treat about 1/2 cases of Homocystinuria
give very high dosage of vitamin B6
What is VitB6 and its characteristics?
water soluble, not toxic vitamin
Why does treatment of high dosage of Vitamin B6 only work for half the cases?
mutation decreases cofactor binding or another mutation that could affect substrate binding, etc.
What enzyme is defective in maple syrup urine disease?
Branched-chain α-keto acid dehydrogenase complex
What does BCKDC stand for?
Branched-chain α-keto acid dehydrogenase complex
In maple syrup urine disease there are defective metabolism of branched-chain aa:
Val, Leu, Ile
What leads to pathology of maple syrup urine disease
accumulation of branched chain aa
What is clinical presentation of maple syrup urine disease?
mental retardation
seizures
urine - sweet smell (like maple syrup)
fatal if untreated
How do you treat maple syrup urine disease?
dietary restriction of branched-chain aa via artifical diet
Are Val, Leu, Ile essential aa?
yes
What are hemoglobinopathies?
defect in hemoglobin
what is basic structure of hemoglobin?
tetramer- has 4 subunits
What is hemoglobin function in RBC?
oxygen carrier in RBC
each subunit have what in hemoglobin?
heme & iron that oxygen binds to
every hemoglobin tetramer can carry how many oxygen molecuels?
4
What are the two broad categories of hemoglobinopathies?
structural varients
thalassemias
describe the hemoglobin structural varients
defectiv polypeptide, protein still there but does not function correctly. usually due to beta globin mutation
what is most important beta globin hemoglobin mutation?
sickle cell disease
where is mutation in thalassemias?
in alpha or beta globin
what leads to pathology of disease in thalassemias?
imbalance of relative amounts of alpha and beta chains
What is MOI in hemoglobinopathies
AR
What is MOI in hemoglobinopathies
AR
where does the majority of hemoglobinopathy incidence occur?
tropical parts of world (like sickle cell)
HbS stands for what
sickle cell
–/aa (alpha) is most common in what population?
SE asian & china
Beta0 is most common in what population?
italian/greek
alpha and beta globin belong to what?
families
alpha globin cluster on what chromosome
16
bet algobin cluster on chromosome what?
11
how did globin gene families arise?
gene duplications
on alpha globin locus there’s duplications, most of them are what?
non-functional
how many genes are there for alpha globin?
two
describe the relationship of the two alpha globin genes
they are expressed at the same level, very similar
does alpha or beta globin family have more functional genes
beta
during development different genes are expressed @ different times, describe how gene expression occurs on alpha globin locust?
it starts on zeta globin and then moves right
what is the first alpha globin expressed?
zeta globin
when is zeta globin used?
just in early embryogenesis
what is first beta globin expressed
epsilon
what is second beta globin expressed
gamma
what are main forms of beta globin expressed in adults?
beta globin (and very small amounts of delta globin)
When does gamma beta globin end?
6 months after birth
delta globin is expressed when?
very low levels throughout life, starts being expressed just after birth
Hemoglobin A is what?
adult form of hemoglobin
Hemoglobin A2 is what
variant adult hemoglobin
Alpha and delta
fetal hemoglobin is what?
hemoglobin F: alpha and gamma globin
gower 1 is what hemoglobin?
embryonic
If BH4 synthesis or recycling is defective what are the two results?
Hyperphenylalaninemia
Deficiency of catecholamines and serotonin
Why will mental retardation still occur if a pt with BH4 defieicency is put on a Phe restricted diet?
there is still deficiency of neurotransmitters
What are the three important aa in BH4 defeciency?
Tyrosine, Tryptophan, Phenylalanine
Tyr, Trp, Phe
What is important product of tyr hydroxylase pathway?
NE & E
noepinepherine & epinepherine
What is important product of trp hyrxoylase pathway?
serotonin
What does Hb stand for?
hemoglobin
What is the composition of HbA?
two alpha and two beta hemoglobin
What is the composition of HbA2?
two alpha and two delta
What is the composition of HbF?
two alpha & two gamma
What is the composition of Hb Gower 1?
two zita and two epsilon
At what age would you find HbF?
fetus
At what age would you find Hb Gower 1?
embryo
HbF has higher affinity for oxygen than what, and why is it important?
HbA - allows transport of oxygen from mom to baby
Expression of hemoglobin is controlled by what?
LCR
What is LCR
an enhancer
What does LCR stand for?
locus control region
In embryonic DNA LCR would drive expression of what?
epsilon
In fetal DNA LCR would drive expression of what?
gamma
In adult DNA LCR will drive expression of what?
Beta and some delta
Hemoglobinopathies: structural variants, describe
normal amount of protein is produced but the protein that is produced is abnormal
HbC is what mutation
beta: same codon as HbS, codon 6 glu to lys
E6K
How will normal hemoglobin vs. sickle cell migrate differently on gel?
sickle cell migrates more slowly, not as negatively charged
How does HbC run on gel compared to HbS and normal Hb?
HbC runs slower than both of them
What is milder than sickle cell, no sickling of RBCs, asymptomatic, mild hemolytic anemia, splenomegaly
HbC
What is a thalassemia caused by?
imbalance in production of globin chains
The imbalance in production of globin chains causes what?
accumulation of free globin chains → insoluble, preciptate
What is Heinz body?
inclusion of denatured hemoglobin
What is hemolysis?
the rupture or destruction of red blood cells.
What is being produced less in alpha thalassemia?
alpha globin is decreased or absent
What kind of mutation normally occurs in alpha thalassemia?
gene deltions
Chromosme 16 has how many copies of alpha globin gene
2 identical copies
How many forms of alpha thalassemia are there?
4
What are the four forms of alpha thalassemia?
silent carrier
alpha thalassemia trait
hemoglobin H disease
hydrops fetalis
What is the clinical presentation of silent carrier of alpha thalassemia
none
what is the clinical presentation of alpha thalassemia trait
none or minimal anemia under stress
what is the clinical presentation of hemoglobin H disease
microcytic, hypochromic anemia
What is the clinical presentation of hydrops fetalis?
lethal in utero
HbH and Hb Barts have what important characteristics?
insoluble
If three genes are deleted what form of alpha thalassemia is it?
hemoglobin H disease
If two genes are deleted what form of alpha thalssemai is it?
alpha thalassemia trait
a-/a- means what
a alpha gene is deleted on each chromosome
a-/a- are called what?
alpha heterozygote
a+-thal means what
alpha thalassemia trait
What form of alpha thalassemia could a parent have a child with hydrops fetalis?
only when an entire chromosome doesn’t have any correct alpha hemoglobin, as parent donates their entire chromosome
What kind of hemoglobin is produced in hydrops fetalis?
Hb Barts
severe anemia, edema, heart failure, fatal in utero in 3rd trimester is what sdiseae?
hydrops fetalis
–/– is what alpha thalassemia disease/
hydrops fetalis
Does a pt with hydrops fetalis have alpha hemoglobin?
no
a-/– is what alpha thalassemia disease?
HbH disease
How much alpha globin is produed in HbH disease?
25%
What is kind of hemoglobin is produced in HbH disease?
HbH (4 beta)
microcytic, hypochromic anemia, hepatomegaly, splenomegaly is what disease?
HbH disease
What does HbCS stand for?
Hb Constant Spring
where is mutation in HbCS?
in alpha globin, a nonstop mutation
what is a nonstop mutation
stop codon changed to aa codon
describe what happens to cause HbCS
stop codon ismutated to aa codon resulting in longer protein
Describe the RNA in HbCS
unstable
HbCS is phenotypically similar to what
HbH
Which forms of hemoglobin have very high affinities for oxygen but do not release the oxygen into the tissues?
Hb Barts, HbH, HbCS
Since the two HBA genes are identical, what cn happen in meiosis
homologous recombination
unequal crossing over
what is the result of unequal crossing over of HBA genes
one chromosome will lose a copy of gene and the other will gain a copy
What is the result of having 3 copies of HBS on one chromosome
no change in phenotype
What is the result of having 3 copies of HBS on one chromosome
no change in phenotype
What is wrong in beta thalassemia
synthesis of beta globin is decreased or absent
what does HBB stand for
beta globin
when does phenotype usually present in beta thalassemia and why
in 1st year, after birth, beta globin doesnt take over until after birth
What is the name of the heterozygous carrier state for beta thalassemia
beta thalassemia minor
what is the phenotype of beta thalassemia minor
asymptomatic
how much beta globin is present in beta thalassemia major
none
what is the normal mutation for beta thalassemia major
null mutation
what disease has severe microcytic hypochromic anemia, hepatosplenomegly, ,bone marrow expansion, skeletal changes, require regular blood transfusions (iron overload secondary to transfussions)
β-Thalassemia Major
What is the main form of beta thalassemia major
β° Thalassemia
What is beta thalassemia intermedia
like β° Thalassemia but less severe
What is the normal mutation for mutations in beta thalassemia vs alpha
null mutations with no functional protein produced
Not complete deletions (like alpha)
what is the most common cause of beta thalassemia
point mutations
what do missense mutations usually result in
specific structural disorders with different specific phenotypes, not thalassemias
How is Hb Lepore caused by what?
unequal crossing over b/w beta globin and delta globin
How do beta and delta gobin have crossing over
they are so similar they can misalign
What is the result of crossing over of beta and delta globin
it will be a hybrid gene, so part delta part beta
what is the issue in Hb lepore
not enough beta globin being produced because delta globin is expressed at very low levels
why is beta globin expressed at low levels in Hb lepore
because of the crossing over its a gene hybrid and the recombined gene uses promoter from delta globin
why is beta globin expressed at low levels in Hb lepore
because of the crossing over its a gene hybrid and the recombined gene uses promoter from delta globin
Is the recombined beta delta gene in Hb lepore functional?
yes but expressed at low levels so presents as beta thalassemia
Is the recombined beta delta gene in Hb lepore functional?
yes but expressed at low levels so presents as beta thalassemia
What does HPFH stand for
Hereditary Persistence of Fetal Hemoglobin
What is phenotype of HPFH
normal
What causes HPFH?
deletions of beta globin & delta globin
In HPFH what does LCR activate?
gamma globin promoters
What does AIP stand for?
acute intermittent porphyria
What is the major acute hepatic porphyria?
AIP
What is deficient in AIP?
porphobilinogen deaminase
What is MOI for AIP?
AD
Clinical presentation: Latent prior to puberty
Abdominal pain, weakness
Neuropsychiatric disturbances, hallucinations
Wine red urine
No photosensitivity
Exacerbated by hormones, drugs & diet
is what disease?
AIP
What is the less common acute hepatic porphyria?
VP
What does VP stand for?
variegate porphyria
What is deficient in VP?
Protoporphyrinogen oxidase
clinical presentation: Abdominal pain, weakness
Neuropsychiatric disturbances, hallucinations
Photosensitivity
Exacerbated by hormones, drugs & diet
is what disease?
VP