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IMS > Topic 11 - Clinical Genetics > Flashcards

Topic 11 - Clinical Genetics Flashcards

1
Q

What are the three general categories of genetic factors causing disease?

A
  • Environmental
  • Monogenic
  • Polygenic
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2
Q

What are the five actual classifications of genetic disorders?

A
  • Multifactorial
  • Monogenic
  • Chromosomal
  • Mitochondrial
  • Somatic Mutations (cancer)
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3
Q

What is the continuum of penetrance?

A

From fully penetrant conditions where environmental factors have no effect, to low-penetrance conditions where genes only play a small part

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4
Q

What is an example of a multifactorial disease?

A

Multiple sclerosis - genetic factors play a major role in determining susceptibility, but each individual factor has low penetrance

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5
Q

What does a mutation in a single gene usually cause?

A

Loss of function

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6
Q

What do variants in multiple genes usually cause?

A

Alternation of function

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7
Q

What do chromosomal imbalances usually cause?

A

Alternations in gene dosage

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8
Q

What are multifactorial genetic disorders?

A
  • common
  • environmental influences + genetic disposition = susceptibility to disease
  • variants in genes cause alteration of function
  • one organ system affected
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9
Q

What are single gene disorders?

A
  • 1% liveborn
  • dominant/recessive pedigree patterns
  • mutations in single genes often cause loss of function
  • can affect structural proteins, enzymes, receptors and transcription factors
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10
Q

What are chromosomal disorders?

A
  • 0.6% liveborn
  • thousands of genes may be involved
  • chromosomal imbalance causes alteration in gene dosage - multiple organ systems affected at multiple stages in gestation
  • usually de novo (trisomies, deletions, duplications)
  • in rare cases, can be inherited (translocations)
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11
Q

What does Down’s Syndrome cause?

A
  • Round face
  • Protruding tongue
  • Upslanting palpebral fissures
  • Epicanthic folds
  • Developmental delay
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12
Q

What are palpebral fissures?

A

The palpebral fissure is the elliptic space between the medial and lateral canthi of the two open lids.

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13
Q

What are the epicanthic folds?

A

The epicanthic fold is the skin fold of the upper eyelid, covering the inner corner (medial canthus) of the eye.

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14
Q

What is a trisomy?

A

A trisomy is a chromosomal disorder characterised by an additional chromosome, so the person has 47 instead of 46.

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15
Q

What are the ultrasound features of Trisomy 21?

A
  • short femurs
  • nuchal translucency
  • echogenic bowel
  • choroid plexus cyst
  • sandal gap, single palmar crease
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16
Q

What are the three different patterns of chromosomes that cause Down syndrome?

A
  • 95% have 3 seperate copies of chromosome 21 - trisomy 21
  • 4% have an extra copy of chromosome 21 due to a Robertsonian translocation
  • 1% have mosaicism with normal and trisomy 21 cell lines. Occurs postzygotically
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17
Q

What is trisomy 18?

A

Edwards Syndrome:

  • 1/3000 births
  • multiple malformations (heart, kidneys)
  • Clenched hands with overlapping fingers
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18
Q

What is trisomy 13?

A

Patau Syndrome:

  • 1/5000 births
  • multiple malformations
  • affects midline structures particularly (incomplete lobation of the brain, cleft lip, congenital heart disease)
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19
Q

What are two conditions caused by sex chromosome number?

A
  • Klinefelter syndrome

- Turner syndrome

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20
Q

What is Klinefelter syndrome?

A
  • 47, XXY
  • 1/1000 males
  • Infertility (atrophic testes do not produce sperm)
  • Poorly developed 2ndy sexual characteristics in some (lack of testosterone)
  • Tall, disproportionately long limbs
  • Hypogonadism
  • Gynecomastia in late puberty
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21
Q

What is Turner syndrome?

A
  • 45, X
  • 1/5000 females
  • 99% are lost spontaneously in pregnancy
  • Short stature
  • Primary amenorrhoea (ovaries involute before birth)
  • Congenital heart disease (coarctation of aorta) in 20%
  • Low hairline, narrow hip development
22
Q

What is hypogonadism?

A

Reduction or absence of hormone secretion or other physiological activity of the gonads (testes or ovaries).

23
Q

What is Gynecomastia?

A

Enlarged Breast Tissue in Men. True gynecomastia is an enlargement of the male breast gland because of a hormonal imbalance, but the appearance of enlarged may breasts may be ascribed to pseudogynecomastia, a symptom of excess fat which deposits on the chest. It can be common and temporary in boys going through puberty.

24
Q

What is azoospermia?

A

The medical condition of a man whose semen contains no sperm

25
Q

What is oligospermia?

A

Deficiency of sperm cells in the semen

26
Q

What are numerical chromosome abnormalities?

A
  • Gain/loss of complete chromosomes
  • Common cause is non-disjunction (usually in ger cells)
  • When in somatic cells - causes mosaicism
  • Often lethal consequences
  • Autosomal monosomies are catastrophic
  • Fewer serious side effects from sex chromosome anomalities
27
Q

What are microdeletions?

A

Chromosomal region is lost: too small to be observed microscopically. Identified by use of specific molecular cytogenetic techniques

28
Q

What is the DiGeorge syndrome?

A

-Caused by 22q11.2 microdeletion
-Small mouth
-Prominent nose
-Congenital heart defects
Hypocalcemia, hypoparathyroidism

29
Q

What is the Williams syndrome?

A
  • Caused by 7q11.23 microdeletion
  • Bright eyes
  • Stellate irides
  • Wide mouth
  • Upturned nose
  • Long philtrum
  • Flattened nasal bridge heart defects
  • Heart defects
  • Overly sociable
30
Q

What is the Prader-Willi syndrome?

A
  • Caused by 15q13 microdeletion
  • Hypotonia and abnormal neurological function
  • Hypogonadism
  • Developmental and cognitive delays
  • Hyperphagia and obesity
  • Short stature
  • Behavioral and psychiatric disturbances
  • Large appetite
31
Q

What is the Cat eye syndrome?

A
  • Caused by 22 inverted duplication
  • Iris coloboma
  • Anal atresia
  • Ear tags/ear pits
  • Heart defects
  • Kidney malformations
32
Q

What are dominant conditions?

A

Heterozygotes with one copy of the altered gene are affected

33
Q

What are recessive conditions?

A

Homozygotes with two copies of the altered gene are affected

34
Q

What are X-linked conditions?

A

Males with one copy of the altered gene on the X-chromosome are affected

35
Q

What is familial hypercholesterolemia?

A
  • Defect on chromosome 19
  • Makes the body unable to remove low density lipoprotein cholesterol from the blood
  • High risk of cardiovascular disease
36
Q

What are examples of autosomal dominant diseases?

A
  • adult polycystic kidney disease
  • Huntington disease
  • neurofibromatosis
  • polyposis coli
37
Q

What are examples of autosomal recessive diseases?

A
  • cystic fibrosis
  • phenypketonuria
  • spinal muscular atrophy
  • congenital adrenal hyperplasia
38
Q

What are examples of X-linked diseases?

A
  • Fragile-X mental retardation syndrome
  • Duchenne muscular dystrophy
  • haemophilia
39
Q

What is the result of Autosomal dominant inheritance?

A

Heterozygotes with one copy of the mutated gene are affected

40
Q

What is the result of Autosomal recessive inheritance?

A

Homozygotes with two copies of the mutated gene are affected

41
Q

What is the result of X-linked inheritance?

A

Males with one copy of the mutated gene on the X-chromosome are affected

42
Q

What is Huntington disease?

A

Progressive brain disorder that causes uncontrolled movements, emotional problems, and loss of thinking ability (cognition). Adult-onset Huntington disease, the most common form of this disorder, usually appears in a person’s thirties or forties.

43
Q

What is Cystic fibrosis?

A

Genetic disorder that affects mostly the lungs, but also the pancreas, liver, kidneys, and intestine. Long-term issues include difficulty breathing and coughing up mucus as a result of frequent lung infections.

44
Q

What is Duchenne muscular dystrophy

A

A genetic disorder characterized by progressive muscle degeneration and weakness. … DMD is caused by an absence of dystrophin, a protein that helps keep muscle cells intact. Symptom onset is in early childhood, usually between ages 3 and 5.

45
Q

What is Leber hereditary optic neuropathy?

A

A mitochondrially inherited degeneration of retinal ganglion cells (RGCs) and their axons that leads to an acute or subacute loss of central vision; this affects predominantly young adult males.

46
Q

What is genomic imprinting?

A

An epigenetic phenomenon that causes genes to be expressed in a parent-of-origin-specific manner.

47
Q

What is the genetic basis of sporadic cancer?

A

Both alleles of a gene become inactivated in a particular somatic cell leading to loss of control of growth and unchecked cell proliferation

48
Q

What is the genetic basis of dominantly inherited familial cancer syndromes?

A

An altered allele is inherited and so is in all body cells containing genetic material. When the second (previously normal) allele of the gene pair becomes inactivated in a particular somatic cell this leads to loss of control of growth and unchecked cell proliferation

49
Q

What is multifactorial inheritance?

A
  • inheritance controlled by many genes with small additive effects (polygenic) plus the effects of the environment
  • one organ system affected
50
Q

What is genetic counselling?

A

process of communication and education which addresses concerns relating to the development and/or transmission of a hereditary disorder

51
Q

What is the process of making a diagnosis in clinical genetics?

A
  1. History (Family & Medical)
  2. Examination
  3. Investigations (Chromosomes, DNA, Biochemical)

IMS (13 decks)

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