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Fitz 9th > 18 - Genetics in Relation to the Skin > Flashcards

18 - Genetics in Relation to the Skin Flashcards

1
Q

The genetic basis of more than 2000 inherited single gene disorders has now been determined, of which _____% have a skin phenotype

A

25

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2
Q

The human genome:
_____ chromosomes
_____ pairs of autosomes
_____ sex chromosomes

A

46
22
2

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3
Q

Autosomes are numbered in (ascending/descending) order of size
Largest: chromosome _____
Smallest: chromosome _____

A

Descending
1
22

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4
Q

_____% of the genome corresponds to protein-encoding exons

A

1.5

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5
Q

As much as _____% of the genome is of unknown function, often referred to as “junk” DNA

A

97

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6
Q

Number of human genes

A

20,000-25,000

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7
Q

Y/N: The human genome is comparable in size and complexity to that of primitive organisms such as the fruit fly

A

Yes

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8
Q

Two chromosomal arms

A

“p” or short arm

“q” arm

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9
Q

The bands are numbered from the centromere (outward/inward)

A

Outward

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10
Q

Ends of the chromosomal arms

Consist of multiple tandem repeats of short DNA sequences

A

Telomeres

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11
Q

Additional repeats are added to telomeres by a protein-RNA enzyme complex known as

A

Telomerase

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12
Q

By measuring the _____, the “age” of somatic cells, in terms of the number of times they have divided during the lifetime of the organism, can be determined

A

Length of telomeres

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13
Q

The chromosome arms are separated by the ______, which is a large stretch of highly repetitious DNA sequence

A

Centromere

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14
Q

Where the double chromosomes align and attach during the prophase and anaphase stages of mitosis (and meiosis)
Site of kinetochore formation

A

Centromeres of sister chromatids

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15
Q

Multiprotein complex to which microtubules attach, allowing mitotic spindle formation, which ultimately results in pulling apart of the chromatids during anaphase of the cell division cycle

A

Kinetochore

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16
Q

Collectively code for the amino acid sequence of the protein (or open reading frame)

A

Exons

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17
Q

Exons are separated by noncoding

A

Introns

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18
Q

Y/N: Although all genes are present in all human cells that contain a nucleus, not every gene is expressed in all cells of tissues

A

Yes

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19
Q

The _____ enzyme transcribes the coding strand of the gene, starting from the cap site and continuing to the end of the final exon

A

RNA polymerase II

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20
Q

Initial RNA transcript

Contains intronic as well as exonic sequences

A

Heteronuclear RNA

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21
Q

The primary transcript undergoes splicing to remove the introns, resulting in the _____ molecule

A

Messenger RNA

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22
Q

The bases at the 5’ end (start) of the mRNA are chemically modified

A

Capping

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23
Q

A large number of adenosine bases are added at the 3’ end known as the

A

Poly-A tail

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24
Q

If the mRNA contains a nonsense mutation, otherwise known as a ______, the test round of translation fails

A

Premature termination codon mutation

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25
Q

The genes of prokaryoted, such as bacteria, do not contain ______, so ______ is a process that is specific to higher organisms

A

Introns

mRNA splicing

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26
Q

In some more primitive eukaryotes, RNA molecules contain catalytic sequences known as _____, which mediate the self-splicing out of introns

A

Ribozymes

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27
Q

Y/N: A single gene can encode several functionally distinct variants of a protein

A

Yes

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28
Q

Base pairs at the beginning of an intron

A

5’ splice site or splice donor site

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29
Q

Base pairs at the end of an intron

A

3’ splice site or splice acceptor site

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30
Q

The mRNA contains two untranslated regions (UTR)

A
  1. 5’ UTR upstream of the initiating ATG codon

2. 3’ UTR downstream of the terminator

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31
Q

Stop codon

A

TGA
TAA
TAG

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32
Q

Whereas the _____ UTR can and often does possess introns, the _____ UTR of more than 99% of mammalian genes does not contain introns

A

5’

3’

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33
Q

The natural stop codon is always followed immediately by the

A

3’ UTR

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34
Q

Gene expression is largely determined by the _____ elements of the gene

A

Promoter

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35
Q

In general, the most important region of the promoter is the stretch of sequence immediately upstream of the

A

Cap site

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36
Q

Proteins that either bind to DNA directly or indirectly by associating with other DNA-binding proteins
Binding of these factors to the promoter region of a gene leads to activation of the transcription machinery

A

Transcription factors

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37
Q

Involves studying pedigrees of affected and unaffected individuals and isolating which bits of the genome are specifically associated with the disease phenotype

A

Genetic linkage

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38
Q

Involves first looking for a clue to the likely gene by finding a specific disease abnormality

A

Candidate gene approach

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39
Q

Genetic code of two healthy individuals may show a number of sequence dissimilarities that have no relevance to disease or phenotypic traits

A

Polymorphisms

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40
Q

Single nucleotide polymorphisms do not change the amino acid composition

A

Silent mutation

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41
Q

Some single nucleotide polymorphisms do change the nature of the amino acid

A

Missense change

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42
Q

Mutations which lead to premature termination of translation

A

Nonsense mutations

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43
Q

Deletion of _____ nucleotides (or multiples thereof) will not significantly perturb the overall reading frame

A

Three

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44
Q

Half the normal amount of protein is insufficient for function

A

Haploinsufficiency

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45
Q

Alterations in the gene sequence close to the boundaries between the introns and exons

A

Splice site mutations

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46
Q

Y/N: Mutations within one gene do not always lead to a single inherited disorder

A

Yes

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47
Q

Other transacting factors may further modulate phenotypic expression

A

Allelic heterogeneity

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48
Q

Some inherited diseases can be caused by mutations in more than one gene

A

Genetic (or locus) heterogeneity

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49
Q

The same mutation in one particular gene may lead to a range of clinical severity in different individuals
Variability in phenotype produced by a given genotype

A

Expressivity

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50
Q

If an individual with such a genotype has no phenotypic manifestations

A

Nonpenetrant

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51
Q

Four main patterns of inheritance

A

Autosomal dominant
Autosomal recessive
X-linked dominant
X-linked recessive

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52
Q

One parent is affected unless there has been a de novo mutation in a parental gamete
Males and females are affected in approximately equal numbers
Can be transmitted from generation to generation

A

Autosomal dominant

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53
Q

In affected individuals with autosomal dominant disorders, the risk of transmitting the disorder is _____% for each of their individual

A

50

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54
Q

Any offspring that are affected by an autosomal dominant disorder will have a _____% risk of transmitting the mutated gene to the next generation, but for any unaffected offspring, the risk of the next generation being affected is _____

A

50

Negligible

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55
Q

Distinguish autosomal dominant from X-linked dominant disorders
Best hallmark of autosomal dominant inheritance

A

Male-to-male transmission

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56
Q

Phenotype in heterozygous individuals is less than that observed for homozygous subjects

A

Semidominant

58
Q

Both parents are carriers of one normal and one mutated allele for the same gene, and typically, they are phenotypically unaffected

A

Autosomal recessive

59
Q

If both mutated alleles from both parents are transmitted to the offspring, this will give rise to an autosomal recessive, the risk of which is _____%

A

25

60
Q

Mutations from both parents are the same

A

Homozygote

61
Q

Different parental mutations within a gene have been inherited

A

Compound heterozygote

62
Q

More common in consanguineous families

A

Autosomal recessive

63
Q

If the partner of an individual with an autosomal recessive disorder is also a carrier of the same mutation, albeit clinically unaffected, then there is a 50% chance of the offspring inheriting two mutant alleles and therefore also inheriting the same autosomal recessive disorder

A

Pseudominant

64
Q

Examples of autosomal recessive disorders

A

Lamellar ichthyosis
Xeroderma pigmentosum
Junctional epidermolysis bullosa
Kindler syndrome

66
Q

Examples of X-linked dominant disorders

A

Conradi-Hunermann-Happle syndrome
Incontentia pigmenti
Focal dermal hypoplasia
X-linked dominant protoporphyria

67
Q

Occur almost exclusively in males, but the gene is transmitted by carrier females, who have the mutated gene only on one X chromosome (heterozygous state)

A

X-linked recessive

68
Q

Normally random process that inactivates either the wild-type or mutated X chromosome in each cell during the first weeks of gestation and all progeny cells
In X-linked recessive disorders, females can show some features because of this

A

Lyonization

69
Q

Examples of X-linked recessive disorders

A 
Hypohidrotic ectodermal dysplasia
X-linked ichthyosis
Wiskott-Aldrich syndrome
Fabry disease
Menkes syndrome
70
Q

Abberations in chromosome number or structure occur in about _____% of all conceptions, although most of these lead to miscarriage, and the frequency of chromosomal abnormalities in live births is about _____%

A

6

0.6

71
Q

Number and arrangement of the chromosomes

A

Karyotype

72
Q

Most common chromosomal numerical abnormality

A

Trisomy

73
Q

Presence of an extra chromosome

A

Trisomy

74
Q

Loss of a complete chromosome

A

Monosomy

75
Q

Loss of part of a chromosome

A

Deletion

76
Q

If two chromosomes break, the detached fragments may be exchanged

A

Reciprocal translocation

77
Q

If translocation involves no loss of DNA

A

Balanced translocation

78
Q

Inheritance of both copies of a chromosome pair from just one parent

A

Uniparental disomy

79
Q

Presence of a pair of chromosome homologs from just one parent

A

Uniparental heterodisomy

80
Q

Two identical copies of a single homolog from just one parent

A

Uniparental isodisomy

81
Q

Mixture uniparental heterodisomy and uniparental isodisomy

A

Meroisodisomy

82
Q

Uniparental disomy can result in distinct phenotypes depending on the parental origin of the chromosomes
Means that, during development, the parental genomes function unequally in the offspring

A

Genomic imprinting

83
Q

Most common examples of genomic imprinting

A

Prader-Willi and Angelman syndromes

84
Q

Can result from maternal uniparental disomy for chromosome 15

A

Prader-Willi syndrome

85
Q

Can result from paternal uniparental disomy for chromosome 15

A

Angelman syndrome

86
Q

Three phenotypic abnormalities commonly associated with uniparental disomy for chromosomes with imprinting

A
  1. Intrauterine growth retardation
  2. Developmental delay
  3. Short stature
87
Q 
Small head with flat face
Short and squat nose
Ears small and misshape 
Slanting palpebral fissures
Thickened eyelids
Eyelashes short and sparse
Shortened limbs, lax joints
Fingers short, sometimes webbed
Hypoplastic iris, lightee outer zone (Brushfield spots)
A

Trisomy 21

Down syndrome

88
Q 
Severe mental deficiency
Abnormal skull shape
Small chin, prominent occiput
Low-set, malformed ears
“Rocker bottom” feet
Short sternum
Malformations of internal organs
Only 10% survive beyond first year
A

Trisomy 18

Edwards syndrome

89
Q 
Mental retardation
Sloping forehead because of forebrain maldevelopment (holoprosencephaly)
Microphthalmia or anophthalmia
Cleft palate or cleft lip
Low-set ears
“Rocker bottom” feet
Malformations of internal organs
Survival beyond 6 months is rare
A

Trisomy 13

Patau syndrome

90
Q 
Microcephaly
Mental retardation
Hypospadias
Cleft lip or cleft palate
Low-set ears, preauricular pits
A

Chromosome 4, short arm deletion

91
Q

Mental retardation
Microcephaly
Cat-like cry
Low-set eats, preauricular skin tag

A

Chromosome 5, short arm deletion

92
Q

Hypoplasia of midface
Sunken eyes
Prominent ear antihelix
Multiple skeletal and ocular abnormalities

A

Chromosome 18, long arm deletion

93
Q

Early embryonic loss; prenatal ultrasound findings of cystic hygroma, chylothorax, ascites and hydrops
Short stature, amenorrhea
Broad chest, widely spaced nipples
Wide carrying angle of arms
Low misshapen ears, high arched palate
Short fourth and fifth fingers and toes
Skeletal abnormalities, coarctation of aorta

A

45 XO

Turner syndrome

94
Q

No manifestations before puberty
Small testes, poorly developed secondary sexual characteristics
Infertility
Tall, obese, osteoporosis

A

47 XXY

Klinefelter syndrome

95
Q

Similar to Klinefelter syndrome

A

48 XXYY

96
Q

Phenotypic males (tall)
Mental retardation
Aggressive behavior

A

47 XYY

97
Q

Low birth weight
Slow mental and physical development
Large, low-set, malformed ears
Small genitalia

A

49 XXXXY

98
Q

Mental retardation
Mild dysmorphism
Hyperextensible joints, flat feet

A

Fragile X syndrome

99
Q

An affected male transmits the disorders to all his daughters and to none of his sons
Almost always limited to females; affected males may be aborted spontaneously or die before implantation

A

X-linked dominant

100
Q

Examples of autosomal dominant disorders

A 
Icthyosis vulgaris
Neurofibromatosis
Tuberous sclerosis
Darier disease
Hailey-Hailey disease
109
Q

Segmental mosaicism for autosomal dominant disorders is thought to occur in one of two ways:

A
  1. Type 1 - postzygotic mutation with the skin outside the segment and genomic DNA being normal
  2. Type 2 - heterozygous genomic mutation in all cells that is then exacerbated by loss of heterozygosity within a segment or along the lines of Blaschko
110
Q

Lines of migration and proliferation of epidermal cells during embryogenesis

A

Lines of Blaschko

111
Q

Refers to genetic correction of an abnormality be various different phenomena

A

Revertant mosaicism

Natural gene therapy

112
Q

Mosaicism can also be influenced by environmental factors

A

Epigenetic mosaicism

113
Q

The human leukocyte antigen is located on the short arm of chromosome 6, at 6p21, referred to as

A

Major histocompatibility

114
Q

Three classic loci at HLA class I

A

HLA-A
HLA-B
HLA-Cw

115
Q

Five loci at HLA class II

A 
HLA-DR
HLA-DQ
HLA-DP
HLA-DM
HLA-DO
116
Q

Contributes to defining a unique “fingerprint” for each person’s cells, which allows an individual’s immune system to define what is foreign and what is self

A

HLA molecules

117
Q

HLA haplotype: psoriasis

A

HLA cw6

118
Q

HLA haplotype: alopecia areata

A

HLA DWB1*03
HLA DR4
HLA DQ7

119
Q

HLA haplotype: psoriatic arthropathy

A 
HLA B27
HLA B7
HLA B13
HLA B16
HLA B38
HLA B39
HLA B17
HLA cw6
120
Q

HLA haplotype: dermatitis herpetiformis

A

HLA DQw2

121
Q

HLA haplotype: pemphigus

A

HLA DR4

HLA DQ1

122
Q

HLA haplotype: reactive arthritis syndrome

A

HLA B27

123
Q

HLA haplotype: Behcet disease

A

HLA B51

124
Q

HLA haplotype: increased risk for carbamazepine-induced SJS and TEN

A

HLA-B*1502

125
Q

Additional influences at the biochemical, cellular, tissue, and organism levels occur

A

Epigenetic phenomena

126
Q

Mammalian DNA methylation machinery is made up of two components

A
  1. DNA methyltransferases

2. Methyl-CpG-binding proteins

127
Q

Establish and maintain genome-wide DNA methylation patterns

A

DNA methyltransferases

128
Q

Involved in scanning and interpreting the methylation patterns

A

Methyl-CpG-binding proteins

129
Q

Analysis of any changes in DNA methylation

A

Epigenomics

130
Q

DNA (hyper-/de-)methylation contributes to gene silencing by preventing the binding of activating transcription factors and by attracting repressor complexes that induce the formation of inactive chromatin structurez

A

Hyper

131
Q

Fetal DNA from amniotic cells taken at

A

16 weeks AOG

132
Q

Fetal DNA from samples of chorionic villi taken at

A

10-12 weeks AOG

133
Q

Treatment of (dominant/recessive) genetic diseases with gene therapy are generally technically more feasible than treatment (dominant/recessive) genetic conditions

A

Recessive

Dominant

134
Q

Treatment of dominant-negative genetic disorders
Patients already carry one normal copy of the gene as well as one mutated copy - where one normal allele is sufficient for skin function, suppression of expression of the dominant negative mutant allele should be therapeutically beneficial

A

Gene inhibition therapy

135
Q

Using an (in vivo/ex vivo) approach, the gene therapy agent would be delivered directly to the patient’s skin or another tissue

A

In vivo

136
Q

In an (in vivo/ex vivo) approach, a skin biopsy would be taken. Keratinocytes or fibroblasts would be expanded in culture, treated with the gene therapy agent, and then grafted onto or injected back into the patient

A

Ex vivo

137
Q

Expressing the normal complementary DNA encoding the gene of interest from some form of gene therapy vector adapted from viruses that can integrate their genomes stably into the human genome

A

Gene replacement therapy

138
Q

Small synthetic double-stranded RNA molecules of 19 to 21 bp that can efficiently inhibit expression of human genes in a sequence-specific, user-defined manner

A

Short inhibitory RNA

139
Q

Main obstacles in developing topical short inhibitory RNA therapied

A

Rapid degradation

Poor cellular uptake

142
Q

Mitochondrial disorders are inherited solely from the

A

Mother

143
Q

Mitochondrial DNA has the capacity to form a mixture of both wild-type and mutant DNA within a cell, leading to cellular dysfunction only when the ratio of mutated to wild-type DNA reaches a certain threshold

A

Heteroplasmy

144
Q

Predominant technology for mapping complex diseases

A

Genome-wide association studies

145
Q

Involves collecting DNA from a well-phenotyped case series of the condition of a choice, preferably from an ethnically homogenous population

A

Genome-wide association studies

146
Q

Currently the method of choice in mapping complex disease genetics

A

Single nucleotide polymorphisms-based genome-wide association studies

147
Q

Presence of a mixed population of cells bearing different genetic or chromosomal characteristics leading to phenotypic diversity

A

Mosaicism

148
Q

Mosaicism for a single gene

Indicates a mutationsl event occurring after fertilization

A

Somatic mosaicism

149
Q

The (earlier/later) mosaicism occurs, the more likely it is that there will be clinical expression of a disease phenotype as well as involvement of gonadal

A

Earlier

150
Q

Mosaicism with involvement of both gonads and somatic tissue

A

Gonosomal mosaicism

151
Q

Mosaicism the occurs eclusively in gonadal tissue

A

Gonadal mosaicism

Fitz 9th (108 decks)

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