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MHG - Exam 2 > Lecture 20-Introduction to Clinical Genetics > Flashcards

Lecture 20-Introduction to Clinical Genetics Flashcards

0
Q

how much of the infant mortality rate can be attributed to birth defects and genetic etiologies?

A

1/3

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1
Q

How many genes do we have on each chromosome?

A

100s-1000s

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2
Q

How many newborns are born with some type of birth defect?

A

2-3%

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3
Q

Birth defects/genetic disorders are major contributors to _______

A

developmental disabilities

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4
Q

genetic disorders and consgential anomalies account for how many pediatric hospital admissions?

A
  • 50%
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5
Q

What is the prevalence for specific gene disorders?

A
  • 1/500
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6
Q

What is the prevalence for chromosome disorders? Chromosome disorders give rise to how many of the children with severe MR and multiple congenital anomalies (MCA)?

A
  • 0.7%

- 10-15%

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7
Q

Single gene disorders are also called______. What kind of inheritance do they exhibit?

A
  • mendelian conditions

- characteristic

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8
Q

The majority of single gene conditions are _____ but their combined effect is ______.

A
  • rare

- significant

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9
Q

Chromosome disorders

- Inheritance pattern?

A
  • caused by a deficiency of a chromosome segment or entire chromosome
  • not inherited usually
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10
Q

Symptoms of chromosome disorders? (3)

A
  • MR, physical retardation
  • unique physical features
  • congenital anomalies
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11
Q

Symptoms of sex chromosome disorders?

A
  • mild developmental/behavioral problems
  • tall or short stature
  • infertility
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12
Q

pseudogenes

A
  • may or may not be transcribed

- don’t lead to an end function

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13
Q

how big is a mutation?

A
  • single bp OR

- large segment of chromosome

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14
Q

Inherited mutations

- also called _______

A
  • mutations in a germ cell and is present throughout every cell in a persons body their entire life
  • germline mutation
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15
Q

what is a germline de novo mutation?

A
  • a mutation not inherited from a parent but occurs in a fertilized egg
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16
Q

Acquired mutations

  • caused by what?
  • also called _______
A
  • mutations that occur during a person’s life in somatic cells. Usually caused by enviromental factors (UV), viruses, DNA replication mistake
  • somatic mutations
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17
Q

Can somatic mutations be inherited?

A
  • no
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18
Q

Polymorphism

A

allele sequence in 1% or more of the population

  • considered a normal finding
  • can contribute to multifactorial disorders
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19
Q

Rare variant

A
  • allele sequence in <1% of the population
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20
Q

nonsense mutation

A
  • stops protein from being transcribed
21
Q

missense mutation

A
  • “misspelling” of the protein
22
Q

Give an ex of a loss of function mutation. What does this protein impact and what are the effects of having this gene mutated?

A

RB1–retinoblastoma

  • tumor suppressor that regulates the cell cycle
  • both copies must be mutated to have loss of function
23
Q

What are the different ways that a child can develop retinoblastoma from the loss of function mutation and what are the frequency and outcomes of each(2)?

A
  • One mutated allele inherited an the other acquires the mutation (40%).
  • bilateral, early onset Rb
  • both alleles of Rb acquire the mutation somatically (60%)
  • unilateral, late onset in childhood
24
Q

Give an ex of a gain of function mutation. What does this protein impact and what are the effects of having this gene mutated?

A
  • FGFR3 (normally inhibits cartilage cell growth)
  • keeps FGFR3 on constitutively even without FGF so cartilage cells are constantly inhibited
  • achondroplasia
25
Q 
Dominant negative (2)
- example?
A
  • a mutation in one allele disrupts or antagonizes the function or product of the other allele
  • usually related to structural proteins
  • mutation in Type I collagen resulting in inability to form collagen and therefore osteogenesis imperfecta
26
Q

Clinical/phenotypic heterogeneity

A
  • mutations in the same GENE (can be in different places on the gene) give rise to different phenotypes
27
Q

Types of genetic heterogeneity?

A
  • allelic

- locus

28
Q

allelic heterogeneity

A
  • different mutations/alleles give rise to similar phenotype
29
Q

locus heterogeneity

A
  • different genes (and therefore loci) give rise to a similar phenotype
30
Q

Give an example of clinical heterogeneity.

A
  • RET gene
  • MEN2B (thyroid carcinoma, neuromas of the lips and tongue, etc.) and Hirschsprung Disease (congenital aganglionic megacolon)
31
Q

Give an example of allelic heterogeneity.

A

CFTR (cystic fibrosis transmembrane conductance regulator) mutations can block different steps within the pathway leading to the same phenotype

32
Q

Give an example of locus heterogeneity.

A
  • retinitis pigmentosa
  • 339 genetic syndromes have this as a feature
  • varied inheritance (AD, AR, XL)
33
Q

Phenocopy

- example?

A

an environmentally induced condition that mimics/is very similar to a phenotype caused by a specific genotype

  • 22q11 deletion/DiGeorge syndrome and retinoic acid embryopathy
34
Q

teratogens (3)

A
  • agents that cross the placental barrier
  • cause structural and functional malformations, growth deficiency
  • account for a SMALL percentage of congenital malformations
35
Q

What are the categories of teratogens (5)

A
  • Rx drugs (thalidomide, Fetal hydantoin syndrome)
  • illicit substances (FAS)
  • chemical/physical agents
  • maternal metabolic/genetic factors (maternal diabetes)
  • infectious agents
36
Q

Pleiotropy

- example?

A
  • multiple phenotypic effects of a single gene

- Stickler syndrome causing collagen 2A1 mutations

37
Q

What’s the difference between penetrance and expressivity?

A
  • penetrance: an individual who has the genotype for disease may or may not have signs/symptoms of the disease (on/off switch)
  • expressivity: the extent to which the genetic defect is expressed but is NEVER unexpressed in those who have the genotype (dimmer switch)
38
Q

How do you calculate penetrance?

A
  • # who have disease associated with mutation/# who have mutation
39
Q

Example of a gene that shows varied penetrance when mutated?

A
  • BRCA
40
Q

Example of a disorder that shows varied expressivity?

A
  • achondroplasia: every person with mutation effected by have variable presentations
41
Q

Malformation

- frequencies

A
  • localized abnormalities in organogenesis that are intrinsic to the embryo/fetus
  • can be major (3%) or minor (17%)
42
Q

Dysplasia

A
  • abnormal organization of cells, abnormal tissue development intrinsic to embryo/fetus
  • all components are present but disorganized
43
Q

Deformation

- example?

A
  • extrinsic mechanical force impairs normal ongoing fetal development and can change the shape, form and position of the body
  • oligohydramnios–low amniotic fluid
44
Q

Disruption

- example?

A
  • extrinsic force destroys tissues or organ that had already developed normally
  • 2º limb defect from vascular event
45
Q

Syndrome

- example?

A
  • pattern of anomalies from one single etiology

- Downs

46
Q

Association

- Example?

A
  • grouping of congenital anomalies that are found together more than statistically expected with no known common etiology
  • VACTERL associate
47
Q

Sequence

- Example?

A
  • congenital anomalies from one defect that causes secondary structural changes
  • Robin sequence (mandibular hypoplasia resulting in tongue displacement then cleft palate
48
Q

Finding areas with increased incidence of consanguinity you are more likely to find a higher rate of _______ diseases

A
  • autosomal recessive
49
Q

What are the 3 types of referrals for genetic diagnosis? What are the indications for each?

A
  • prenatal: family history of a disease/disorder; abnormal maternal screening/ultrasound
  • Pediatric: suspected physical external/internal anomalies; growth problems, developmental delays, intellectual disability
  • Adult: suspicion that they may have a genetic disorder based on behavior, mental deterioration, specific medical problems; personal/family history of cancer
50
Q

Successful genetic counseling is contingent upon _______

A

accurate diagnoses!!!

MHG - Exam 2 (11 decks)

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