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MBChB 3 > Genetics > Flashcards

Genetics Flashcards

1
Q

How is acondroplasia inherited?

A

Autosomal dominant. Leads to short stature due to short limbs. FGFR3 mutation.

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2
Q

What is a vertical pattern of inheritance?

A

When in each level of the family tree there is someone affected.

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3
Q

What are modifier genes?

A

Genes that are not the main gene involved in a condition but are still involved.

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4
Q

What is incomplete penetrance?

A

You may inherit the gene but may not actually get the condition eg. BRCA1. High percentage risk of developing it but not 100%.

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5
Q

What is a teratogen?

A

eg. thalidomide. It changes the way genes/proteins work but not in sequence (not a mutagen).

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6
Q

What is a compound heterozygote?

A

When there are different mutations within the same gene.

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7
Q

By what mode is sickle cell anaemia inherited?

A

Autosomal recessive

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8
Q

By what mode is Duchenne muscular dystrophy inherited?

A

X-linked recessive. DMD is due to a mutation which means there is an absence of dystrophin from the muscle fibre membrane, the sarclemma.

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9
Q

What are obligate carriers?

A

In x-linked recessive disorders- females who carry the condition. Males can’t be carriers, they’d have the condition.

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10
Q

What is Ivacaftor?

A

A medication used to treat patients with the G551D mutation which causes cystic fibrosis. This blocks the opening of the CFTR chloride ion channel and Ivacaftor re-opens the channel.

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11
Q

What is Gefitinib?

A

A tyrosine kinase inhibitor used to treat non-small cell lung cancer. Need to check for specific biomarkers before being given the drug.

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12
Q

What is Trastuzumab?

A

Name for Herceptin. Used to treat HER2+ breast cancer.

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13
Q

What is FAP?

A

Familial adenomatous polyposis. An autosomal dominant condition caused by mutations in the APC gene (chrom. 5). Typically results in over 100 colorectal polyps and tendency to develop cancer at an early age. Have annual bowel screening from age 11.

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14
Q

Mutations in what mismatch repair genes cause Hereditary nonpolyposis colorectal cancer?

A

MLH1, MSH2, MSH6 and PMS2.

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15
Q

What is MAP?

A

MYH- associated polyposis. Autosomal recessive inheritance and results in defective base excision repair.

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16
Q

What are stability genes (caretaker genes)?

A

A type of TSGs. They act to minimise genetic alterations. Account for commonest hereditary cancer predisposition syndromes.

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17
Q

BRCA1 breast and ovarian cancer risks?

A

BC: 40-87% risk by age 70
OC: 22-65% risk by age 70

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18
Q

What is the function of BRCA1 and BRCA2 proteins?

A

DNA repair by homologous recombination of double-strand breaks.

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19
Q

What happens if you are at high risk of colorectal cancer?

A
  • 2 yearly colonoscopies from age 25

- 2 yearly upper GI endoscopy from age 50

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20
Q

What is Li Fraumeni syndrome?

A

Rare autosomal dominant cancer predisposition syndrome:
-breast cancer
-brain tumours
-sarcoma
-leukaemia
-adrenocortical carcinoma
Chance of cancer 50% by age 30, 90% by age 50. Due to mutations in master control gene, TP53.

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21
Q

What is replicative senescence?

A

A cell can only divide a certain number of times.

22
Q

What are some of the typical features of autosomal dominant conditions?

A
  • Vertical pedigree pattern
  • Generally equal disease frequency and severity between males and females
  • Variable expressivity
23
Q

What is genetic anticipation?

A

Increasing severity and decreasing age of onset of certain conditions in successive generations. It may results from increasing size, at meiosis, of a tract of trinucleotide repeats, which may lie outside of the coding sequence. Seen in Huntington disease, fragile X syndrome, myotonic dystrophy.

24
Q

Examples of autosomal recessive conditions?

A

Cystic fibrosis, phenylketonuria (PKU), spinal muscular atrophy, congenital adrenal hyperplasia.

25
Q

Examples of x-linked dominant inheritance

A

Relatively few examples: vitamin D resistant, incontinentia pigmenti (male lethality), Rett syndrome (usually male lethality).

26
Q

What is pseudo-dominance?

A

If an AR condition but a very high carrier frequency or consanguinity- it appears like AD. eg. Gilbert syndrome. Carrier frequency 50%. Intermittent jaundice due to unconjugated hyperbilirubinaemia.

27
Q

What is mitochondrial inheritance?

A

Much smaller genome, 37 genes, no introns. Inherited only from the mother. Syndromes can often affect muscle, brain and eyes. eg. Leigh’s disease

28
Q

What is gonadal (germline) mosaicism?

A

Germline mosaicism is a result of postzygotic mutation in an individual’s gametes that results in all or a portion of their gametes harboring the mutation for a specific condition that is not otherwise phenotypically expresses in the individual.

29
Q

What is BMD?

A

Becker’s muscular dystrophy. A similar condition to DMD but with a milder phenotype. It results from mutations in the DMD gene. However, as these are not frameshift mutations, they permit the formation of dystrophin protein, albeit in a less functional form than normal.

30
Q

What causes myotonic dystrophy?

A

Unstable length mutation of a CTG repeat. DMPK gene. Affected if 50 or more repeats.

31
Q

What does ‘pre-axial polydactyl’ mean?

A

Extra digit on thumb side.

32
Q

What is Heteroplasmy?

A

Presence of more than one type of organellar genome (mitochondrial DNA or plastid DNA) within a cell or individual. It is an important factor in considering the severity of mitochondrial diseases.

33
Q

Huntingtons Disease

A

Onset between 30 and 50. Progressive chorea (involuntary movements), dementia and psychiatric symptoms. CAG (glutamine) repeat unit- expansion of it causes insoluble protein aggregates and neurotoxicity. AD with genetic anticipation. Up to 35 repeats you are unaffected.

34
Q

Myotonic dystrophy

A

AD with genetic anticipation. Progressive muscle weakness in early adulthood. Also myotonia and cataracts. Unstable length mutation of a CTG repeat. In the transcribed but untranslated region of DMPK gene. Affected in 50 or more repeats.

35
Q

Pathogenic mechanism of myotonic dystrophy?

A

Abnormal DMPK mRNA. Indirect toxic effect upon slicing of other genes eg. the chloride ion channel CLCN1 gene (causing myotonia).

36
Q

How do you diagnose CF?

A

Screening of newborns by immunoreactive trypsin (IRT) level. Confirmation by DNA testing (for CF mutations) and/or sweat testing (for increase chloride concentration).

37
Q

What is the pathogenic mechanism of cystic fibrosis?

A

CFTR mutations- leads to defective chloride ion channel and therefore increased thickness of secretions.

38
Q

What is the most common mutation in CF?

A

F508del. Deletion of phenylalanine (F) at position 508.

39
Q

What is cascade screening?

A

Identification of mutations permits prenatal diagnosis if desired and the subsequent identification of carrier relatives.

40
Q

What is Neurofibromatosis type 1 (NF1)?

A

A multisystem genetic disorder that is characterised by cutaneous findings, most notably café-au-lait spots and axillary freckling (see the images below), by skeletal dysplasias, and by the growth of both benign and malignant nervous system tumors, most notably benign neurofibromas.

41
Q

What are Lisch nodules?

A

Dome-shaped gelatinous masses developing on the surface of the iris. Gold-tan to brown in colour, they may grow up to 2 mm in diameter and attain variable sizes on the same iris. The presence of Lisch nodules is the most common clinical sign of NF1.

42
Q

What does dystrophin do?

A

Forms link between F-actin intracellularly and the dystroglycan complex.

43
Q

What can serum creatinine kinase help diagnose?

A

Creatinine kinase leaks out of damaged muscle fibres into serum (into blood). Boys with DMD will have massively increased levels of SCK from birth ie. before any other symptoms are noticeable.

44
Q

Fragile X syndrome

A

X-linked recessive. Genetic anticipation (due to repeats in the 5’ UTR region of FMR1 gene). Most common inherited cause of significant learning disability.

45
Q

Edwards syndrome

A

Trisomy 18. Small chin, clenched hands with overlapping fingers. Malformations of heart, kidney and other organs.

46
Q

Patau syndrome

A

Trisomy 13. Congenital heart disease is usual. About 50% die within 1 month. Like in Edward syndrome, approx. only 10% survive 1st year, generally with profound learning difficulties. Cleft lip and palate, microphthalmia, abnormal ears, post-axial polydactyly (extra little finger).

47
Q

How do trisomies 13, 18 and 21 normally arise?

A

Through maternal non-disjunction in meiosis. Trisomies more frequent with increased maternal age.

48
Q

What are the two types of DNA sequencing?

A

Sanger (fluorescent dideoxynucleotide) sequencing and next generation (or massively parallel sequencing).

49
Q

With NGS, what can you analyse?

A

Single gene (like Sanger sequencing), several genes all at once (“gene panel”), exome (all the protein coding regions of all the genes, and genome (the entire genome).

50
Q

What is Kallman syndrome?

A

When caused by ANOS1 gene it is an X linked recessive disorder characterised by delayed or absent puberty and an impaired sense of smell.

MBChB 3 (13 decks)

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