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214.201 > Genetic Disorders > Flashcards

Genetic Disorders Flashcards

1
Q

What are the most common genetic disorders in NZ?

A
  • Familial Cancer (Breast, Bowel)
  • Huntington’s Disease
  • Muscular Dystrophies
  • Chromosomal abnormalities
  • Cystic Fibrosis
  • Haemochromatosis
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2
Q

Whatare genotype?

A

The genetic information that is stored in the genetic code

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3
Q

What is DNA?

A

Deoxyribonucleic acid - a stable macromolecule of the genetic information

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4
Q

What are chromosomes?

A

Condensed genetic material of an organism located in nucleus

- 22 autosomal pairs, 1 sex pair

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5
Q

What are genes?

A

Segments of DNA responsible for a particular trait

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6
Q

What are alleles?

A

Different DNA sequences of the same gene in a population

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7
Q

What does these mean?

  • Homozygous
  • Heterozygous
  • Dominant
  • Recessive
A
  • Two same alleles
  • Two different alleles
  • Expressed always
  • Expressed when there are two copies
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8
Q

What are genetic mutations?

A

Biochemical events leading to accidental errors in duplication, rearrangement, or deletion of parts of the genetic code

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9
Q

What is a point mutation?

A

Changes of 1 base for another

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10
Q

How can mutations occur?

A

Inherited (germ) or acquired (somatic)

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11
Q

What are the main types of genetic mutations?

A
  • Single gene (autosomal & sex-linked)
  • Alterations in chromosome number
  • Alterations in chromosome structure
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12
Q

What are single gene disorders?

A

Conditions that are caused by a mutation in a single gene in one, or both copies of the gene
- May be present on an autosome or sex-linked chromosome (X)
- Lead to formation of an abnormal protein or decreased
production of a gene product
- Several mutated genes can lead to the same disorder e.g. childhood deafness caused by 16 mutations

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13
Q

What is Marfan syndrome?

A
  • Single gene disorder
  • 1 in 20, 000 people
  • Mutation on chromosome 15
  • Defect in connective tissue affecting various structure (e.g. skeletal, ocular, & cardiovascular)
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14
Q

What are autosomal disorders?

A
  • Caused by mutations in alleles on autosomes

- Most are recessive (need to mutated alleles to be affected)

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15
Q

What is Phenylketonuria?

A
  • A metabolic disorder caused by elevated levels of phenylalanine that are toxic to the brain. Caused by deficiency in phenylalanine hydroxylase (PAH)
  • Autosomal recessive disorder
  • 1 in 10, 000 people
  • Severity of disease rely on amount of deficiency in PAH
  • Symptoms develop gradually
  • If not treated can cause irreversible brain damage
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16
Q

What are autosomal dominant disorders?

A
  • Mutations needing only 1 mutated allele to cause disorder
  • Onset often delayed
  • Can occur without affected parent due to new mutations of germ cells
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17
Q

What is Huntington’s disease?

A
  • Degenerative brain disorder
  • Causes involuntary movements, nervous system
    deterioration, and eventually death
  • Symptoms include: clumsiness, depression, memory loss, loss of muscle coordination and ability to speak
  • Initial symptoms by the age of 40 → People often pass allele on before they know they have it
  • Death likely to occur within 12-20 years of onset of symptoms
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18
Q

What is reduced penetrance?

A

Carrying the mutation but failing to express it

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19
Q

What is variable expressivity?

A

Mutation which can be expressed differently among individuals

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20
Q

What are X-linked recessive conditions?

A
  • Sex-linked disorders in which an unaffected mother carries one normal and one mutant allele on the X chromosome
  • Condition occurs more frequently in males than females
21
Q

How is the X-linked mutation of red-colour blindness developed?

A
  • It develops from loss or limited function of red or green photopigments (colour-detecting molecules) that are located in cone-shaped cells within the retina
  • Is the most common type of hereditary colour blindness
22
Q

What are atypical single gene disorders?

A 
Mutations not following the Mendelian pattern of inheritance
For example:
- Triplet repeat mutations
- Mutations in mitochondrial genes
- Genomic imprinting
23
Q

What are triple repeat mutations?

A

Characterised by a long repeating sequence of 3 nucleotides in a gene that disrupts its function
For example:
- Huntington’s disease
- Fragile X syndrome

24
Q

What are mutations in mitochondrial genes?

A
  • Mutations in the DNA in the mitochondria rather then nucleus DNA
  • This DNA has an almost exclusive maternal form of inheritance
  • Can affect tissues and organs that are highly dependant on oxidative phosphorylation (e.g., brain, neuromuscular
    system)
25
Q

What are chromosomal disorders?

A
  • Parts of chromosomes are lost or gained or dislocated
  • Can result in abnormal gene number or position
  • If mutation includes chromosome breakage it may disrupt gene function
  • Account for a large proportion of early gestational abortions, congenital malformations, and intellectual disability
26
Q

What are the chromosomal abnormalities? Structure & number?

A

1) Alteration in Structure:
- Deletion
- Duplication
- Inversion
- Ring
- Translocation
2) Alteration in Number
- Monosomy
- Trisomy
- Tetrasomy
- Triploidy

27
Q

What is deletion?

A

Simple loss of a chromosomal segment

28
Q

What is duplication?

A

The presence of two copies of a chromosomal region

29
Q

What is inversion?

A

A segment of a chromosome breaks off and then reattaches in the reversed direction

30
Q

What is a ring chromosome?

A

Breakage and two ends joining to form ring

31
Q

What is Cri Du Chat?

A
  • Genetic disease caused by a heterozygous deletion of the tip of the short arm of chromosome 5
  • 1 in 50, 000 people
    Characteristics:
  • Moon like face
  • Often mentally challenged
  • Distinctive catlike mewing cries as infant
  • Abnormal voice box development
  • GI and cardiac complications
32
Q

What are chromosomal duplications?

A
  • Extra copy of a chromosome region consisting of an extra chromosomal arm or part of an arm
  • Hard to detect and are rare
  • Duplications supply additional genetic material capable of evolving new functions
33
Q

What is first division nondisjunction?

A

Failure of the two chromosomes to separate into one in the first meiotic division

34
Q

What is second division nondisjunction?

A

Failure of the chromosome to separate into halves in the second meiotic division

35
Q

How does down syndrome occur and what is it?

A
  • Trisomy of chromosome 21
  • 95% caused by nondisjunction
  • Increased risk with increased maternal
  • Usually apparent at birth
  • Causes a combination of birth defects including intellectual disability and characteristic facial features
36
Q

What is turner syndrome

A
  • Absence of all or part of one of the female’s X chromosome
  • 1 n 5, 000 people
  • 99% of foetuses spontaneously aborted in 1st trimester
  • Diagnosis is often delayed until late childhood/early adolescence
  • Early diagnosis is important for ongoing assessment and treatment (Growth hormone, Oestrogen therapy for secondary sexual
    characteristics)
  • Women with Turner syndrome have increased morbidity due to cardiovascular disease and gastrointestinal, renal, and endocrine disorders
37
Q

What are multifactorial disorders?

A
  • Usually several genes are involved and no clear pattern of inheritance within a family
  • Often environmental contribution
  • Difficult to predict
  • Risks of recurrence are somewhat increased for close relatives of an affected individual and with severity of disorder
38
Q

When can multifactorial disorders be expressed and what are some examples?

A
  • Foetal life and be present at birth (congenital) e.g. Cleft lip or palate, clubfoot, congenital heart disease
  • Later in life (environmental contribution is likely greater) e.g Alzheimer’s, psychiatric disorders, diabetes, obesity, cancer
39
Q

What are teratogens?

A
  • Environmental agent that produces abnormalities during embryonic or foetal development
    Can act via:
    1) Direct exposure of the pregnant women, foetus or embryo
    2) Exposure to an agent with a slow clearance rate prior to pregnancy
    3) Exposure to a teratogenic agent that caused damage to reproductive cells prior to pregnancy
  • Teratogenic agents include: radiation, environmental chemicals and drugs, infectious agents
40
Q

What is organogenesis?

A
  • Time interval of differentiation and organ development
  • In humans from day 15 to day 60 after conception
  • Insult during the first 2 weeks after fertilisation may interfere
    with implantation causing abortion or early resorption
41
Q

What is epigenetic’s?

A
  • Changes in gene expression without changes in gene sequence
  • Regulate activation and repression of genes
  • Flexible mechanisms (Occur during development as stem cells, also in response to environmental signals)
  • Two main kinds of epigenetic information
    1) Methylation (e.g., genetic imprinting)
    2) Histone modifications
42
Q

How do epigenetic’s work?

A
  • DNA remains the same but histone modifies what markers are genes are transcribed into RNA
  • E.g. neuronal cell will express genes to enable to develop axon and dendrites but this will be suppressed in same genes in liver cell
43
Q

What are prenatal tests for screening?

A
  • Give an estimate of the chance a disorder will occur
  • Identify women < 35 years old with higher risk
    pregnancies who can be offered diagnostic testing
  • Less invasive than diagnostic testing
  • Not a “Yes” or “No” answer
  • False +, False -
44
Q

What is a maternal serum screen?

A
  • Maternal blood test measures the level of specific proteins produced by the foetus & placenta
  • Maternal age + protein levels are combined to produce an estimated risk for chromosome abnormalities and neural tube defects
  • Not applicable for all pregnancies
45
Q

What is a prenatal ultrasound?

A
  • Used for screening (and diagnostic)
  • Non-invasive
  • Higher detection rate when combined with other screening methods (e.g., blood tests)
46
Q

What is Nuchal translucency?

A
  • Measurement of the thickness of the fluid that accumulates under the skin at the back of the neck
  • Helps with detecting Down syndrome
47
Q

What are prenatal diagnostic tests?

A
  • Give a clear answer (usually) about whether or not the foetus has a particular condition
  • Provide the most accurate results
  • Involve invasive procedures which carry a risk of
    miscarriage
  • Are only routinely offered to those at higher risk
48
Q

What is amniocentesis?

A
  • Karyotype from a sample of amniotic fluid
  • Identifies major chromosome anomalies
  • Does not identify gene mutations, very small chromosome changes, or structure and development of the foetus
  • Performed after 14 weeks gestation
  • Risk of miscarriage 1/200
  • Accuracy ~99.5%
49
Q

What is chorionic villis sampling (CVS)?

A
  • Karyotype analysis from a sample of the placenta
  • Identifies major chromosome anomalies
  • Does not identify gene mutations, very small chromosome changes, or structure and development of the foetus
  • Performed 10-12 weeks of gestation
  • Risk of miscarriage 1/100
  • Accuracy ~96%

214.201 (17 decks)

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