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Biochem: genetics Flashcards

1
Q

What is codominance?

A

both alleles contribute to the phenotype of the heterozygote

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2
Q

What is variable expressivity?

A

phenotype varies among individuals with same genotype

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3
Q

What is incomplete penetrance?

A

not all individuals with a mutant genotype show the mutant phenotype

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4
Q

What is pleiotropy?

A

one gene contributes to multiple phenotypic effects

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5
Q

What is imprinting?

A

differences in gene expression depend on whether the mutation is of maternal or paternal origin

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6
Q

What is anticipation?

A

increased severity or earlier onset of disease in succeeding generations

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7
Q

What is loss of heterozygosity?

A

if a patient inherits or develops a mutation in a tumor suppressor gene, the complementary allele must be deleted/mutated before cancer develops (not true of oncogenes)

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8
Q

What is a dominant negative mutation?

A

exerts a dominant effect

a heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning

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9
Q

What is linkage disequilibrium?

A

tendency for certain alleles at 2 loci to occur together more often than expected by change
measured in a population, not in a family, often varies in different populations

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10
Q

What is mosaicism?

A

Occurs when cells in the body differ in genetic makeup due to postfertilization loss or change of genetic information during mitosis (can be germline-produce disease that is not carried by parent’s cells)

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11
Q

What is locus heterogeneity?

A

mutations at different loci can produce the same phenotype

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12
Q

What is heteroplasmy?

A

the present of both normal and mutated mtDNA, results in variable expression in mitochondrial inherited disease

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13
Q

What is uniparental disomy?

A

offspring receives 2 copies of a chromosome from 1 parent and no copies from the other parent
heterodisomy (heterozygous) indicates a meisosi I error
isodisomy (homozygous) indicates a meiosis II error or postzygotic chromosomal duplication of one of a pair of chromosomes and loss of the other of the originial pair

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14
Q

Which allele is not expressed in Prader Willi? Sx?

A

paternal not expressed (and maternal gene is inactivated)

MR, hyperphagia, obesity, hypogonadism, hypotonia

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15
Q

Which allele is not expressed in Angelmans? Sx?

A

maternal allele is not expressed (and paternal gene is inactivated)
MR, seizures, ataxia, inappropriate laughter

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16
Q

What is the most common inheritance of enzyme deficiency diseases?

A

AR

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17
Q

What is hypophosphatemic rickets?

A

X linked dominant disorder resulting in increased phosphate wasting at proximal tubule, results in rickets-like presentation

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18
Q

What are key features of mitochondrial myopathies?

A

usually present with myopathy and CNS disease

muscle biopsy often shows “ragged red fibers”

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19
Q

Cause, sx and inheritance of achondroplasia?

A

defect in FGF3-R, dwarfism, short limbs, large head, normal trank size
advanced paternal age assoc
AD

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20
Q

Caus, sx and inheritand of ADPKD?

A

bitlateral massive enlargement of kidneys due to multiple large cysts, flank pain, hematuria, hypertension, progressive renal failure
PKD1 gene mutation, chromosome 16
assoc w/polycystic liver disease, berry aneurysms, MVP
AD

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21
Q

Cause, sx and inheritance of FAP?

A

AD
colon cvered in polyps that progress to colon cancer unless colon resected
APC on chromosome 5 mutated

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22
Q

Cause, sx and inheritance of Gardner’s syndrome?

A

AD

tumors in colon and other soft tissues

23
Q

Cause, sx and inheritance of familial hypercholesterolemia (hyperlipidemia IIA)?

A

elevated LDL due to defective or absent LDL-R, severe atherosclerotic disease early in life, tendon xanthomas, MI before age 20
AD

24
Q

Cause, sx and inheritance of Osler-Weber-Rendu Syndrome?

A

aka hereditary hemorrhagic telangiectasia
AD
inherited disorder of BVs
telangiectasia, recurrent epistaxis, skin discolorations, AVMs, chronic GI bleeding

25
Cause, sx and inheritance of hereditary spherocytosis?
spheroid erythrocytes due to spectrin or ankyrin defect, hemolytic anemia, increased MCHC, increased viscosity, hemolytic anemia, jaundice splenectomy is curative
26
Cause, sx and inheritance of Huntington's disease?
AD CAG repeat chromosome 4 decreased GABA and ACh in brain cognitive decline, caudate atrophy, chroea
27
Cause, sx and inheritance of marfans?
AD fibrillin 1 gene mutation AAA, floppy mitral valve, subluxation of lenses
28
Cause, sx and inheritance of multiple endocrine neoplasias?
AD familiar tumors of endocrine glands 2A and 2B assoc w/ret gene mutations
29
Cause, sx and inheritance of NF-1?
AD chromosome 17 has mutation cafe au lai spots, neural tumors, lisch nodules, scoliosis/kyphosis, optic pathway gliomas
30
Cause sx and inheritance of NF-2?
AD NF2 gene on chromosome 22 mutated bilateral acoustic schwannomas, juvenile cataracts, balance issues
31
Cause, sx and inheritance of Tuberus sclerosis?
``` AD w/incomplete penetrance/variable presentation facial lesions (adenoma sebaceum), hypopigmented ashleaf spots, cortical and retinal hamartomas, seizures, MR, renal cysts, renal angiomyolipomas cardiac rhabdomyomas, increased incidence of astrocytomas ```
32
Cause, sx and inheritance of von Hippel Lindau?
AD deletion of VHL gene on chromosome 3 (leads to constitutive expression of HIF and activation of angiogenic growth factors) hemangioblastomas of retina/cerebellum/medulla, multiple bilateral renal cell carcinomas and other tumors
33
List the key autosomal recessive disease to know (10)
albiniskm, ARPKD, CF, glycogen storage diseases, hemochromatosis, mucopolysaccharidoses, PKU, sickle cell, sphingolipidoses, thalassemias
34
What is the most common mutation seen in CF? What happens to the protein?
deletion of Phe 508 of CFTR gene on chromosome 7 | causes abnormal folding and usually degradation of channel before reaching cell surface
35
Why can CF cause infertility in men?
bilateral absence of vas deferens
36
What are the most important X linked recessive disorders to know? (10)
``` Bruton's agammaglobulinemia Wiskott-Aldrich s/o Fabry's disease G6PD def Ocular albinism Lesch Nyhan Duchenne's and Beckers Muscular dystrophy Hunter s/o Hemophilia A&B OTC deficiency ```
37
How are muscular dystrophies diagnosed?
increased CPK and muscle biopsy
38
What gene is deleted/mutated in muscular dystrophies?
dystrophin
39
What causes Fragile X s/o? Sx?
Xlinked methylation/expression FMR1 gene affected due to CGG repeat 2 mcc of MR marcroorchidism, long face w/a large jaw, large everted ears, autism or ADHD, MVP short, joint laxity, scoliosis, pes cavus, dbl jointed thumbs, single palmar crease
40
What are the trinucleotide repeat diseases and their trinucleotides?
``` Fragile X=CGG Friedrich ataxia=GAA Huntingons=CAG Myotonic dystrophy=CTG ** these often show anticipation ```
41
What causes Cri-du-chat s/o?
microdeletion of short arm of chromosome 5
42
Sx of cri-du-chat?
microcephaly, MR, high pitched crying/mewing, epicanthal folds, cardiac abnormalities (VSD)
43
What causes Williams s/o?
microdeletion of long arm of chromosome 7
44
sx of williams s/o?
elfin facies, intellectual disability, hypercalcemia (increased Vit D sensitivity), well developed verbal skills, extreme friendliness with strangers, CV problems
45
What can 22q11 deletion syndromes cause?
CATCH-22 cleft palte, abnormal facies, thymic aplasia, carrdiac defects (tetralogy), hypocalemia 2ary to parathyroid aplasia DiGeorge s/o velocardiofacial s/o
46
What is a robertsonian translocation?
nonreciprocal chromosomal translocation that commonly involves chromosome pairs 13,14,15,21,22 common occurs when long arms of 2 acrocentric chromosomes fuse at the centromere and the short arms are lost unbalanced translocations can result in miscarriage, stillbirth and chromosomal imbalance (down's, patau's)
47
What are sx of trisomy 21?
MR (mcc) flat facies, prominent epicanthal folds, simian crease, gap bwn 1st 2 toes, duodenal atresia, congenital heart disease (mc ASD), increased risk of ALL, alzheimers disease
48
What causes trisomy 21?
``` meiodtic nondisjunction (95%)-assoc w/adv mat age robertsonian translocation (4%) down mosaicism (1%) ```
49
What as sx of trisomy 18 (edwards syndrome)?
severe MR, rocker bottom feet, micrognathia, low set ears, clenched hands, prominent occiput, congenital heart disease death within a year usually
50
What are sx of trisomy 13 (patau's syndrome)?
severe MR, rocker bottom feet, microphthalmia, microcephaly, clef lip/palate, holoprosencephaly, polydactyly, congenital heart disease death within first year (may be due to defective sonic hegehog gene)
51
What is seen on pregnancy quad screen w/trisomy 21?
decreased AFP, increased B hCG, decreased estriol, increased inhibin A
52
What may be seen on US during first trimester in tri 21 or with triosmy 13?
increased nuchal translucency
53
What is seen on preg quad screen w/trisomy 18?
decreased AFP, decreased B hCG, decresaed estriol, normal inhibin A
54
What is seen on rpeg quad screen for trisomy 13?
decrased free B hCG, decreased PAPP-A

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