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MCD > Genetics > Flashcards

Genetics Flashcards

1
Q

Aneuploidy of Downs Syndrome

A

Trisomy 21

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2
Q

Clinical features/symptoms of Downs Syndrome

A

Cardiac problems: significant leading to major cardiac surgery
-Septal defects
-Atrioventricular canal
Limb problems:
-Single palmar crease
-Sandal gap (wide gap between the first and second toes)
Craniofacial problems:
-macroglossia (abnormally large tongue)
-small ears
-epicanthic folds (vertical fold of skin from the upper eyelid that covers the inner corner of the eye)
-brushfield spots (tiny white spots around the iris of the eye)
Newborn problems:
-hypotonia (decreased muscle tone=floppy baby syndrome)
-lethargy
-excess nuchal skin
Other problems:
-short stature
-duodenal atresia
-low IQ but advanced social skills

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3
Q

Three different chromosome aberrations leading to Downs Syndrome

A

1) Trisomy 21 (in 95% of cases)
2) Translocation (Robertsonian specifically and in 4% of cases)
3) Mosaicism (1% of cases)=abnormal cell population in the body

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4
Q

Define monosomy

A

Loss of a single chromosome and almost always lethal leading to miscarriage

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5
Q

Define disomy

A

Normal pair of chromosomes

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6
Q

Define trisomy

A

Gain of a single chromosome and can be tolerated for specific chromosomes

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7
Q

Define tetrasomy

A

Gain of 2 chromosomes (although extremely rare) and can be tolerated for specific chromosomes

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8
Q

Aneuploidy of Patau’s Syndrome

A

Trisomy 13

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9
Q

Aneuploidy of Edward’s Syndrome

A

Trisomy 18

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10
Q

Clinical features of Patau’s Syndrome

A 
Cardiac problems:
-Septal defects
-Patent ductal arteriosus
Holopresencephaly (structural malformation of the brain which often affects facial features giving a cleft lip and orbital hypotelorism)
mental retardation
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11
Q

Clinical features of Edward’s Syndrome

A 
Cardiac problems:
-Septal defects 
-Patent ductus arteriosus 
Kidney malformations:
-Horseshoe kidney
Digestive tract defects:
-Omphalocele (where the infants intestine or other abdominal organs are outside of the body because of a hole in the belly button area)
-Oesophageal atresia (upper part of the oesophagus does not connect with the lower part of the oesophagus and the stomach)
Mental retardation
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12
Q

Prenatal features of Turner’s Syndrome

A

-generalised oedema and neck swelling which occurs in the second trimester (13 weeks to 28 weeks)

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13
Q

Clinical features of Turner’s Syndrome in newborns/children

A

-Low posterior hairline
-low set ears
-broad chest
-oedematous hands/feet (both in utero and postnatally)
-webbed neck (characteristic)
-normal intelligence (brain development not impaired)
Aortic defects:
-coarctation (congenital narrowing of a short section of the aorta)
-valve defects
Urinary defects:
-horseshoe kidney

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14
Q

Complications in adults from previous Turner’s Syndrome symptoms

A

-Short stature (averaging 145cm)
Ovarian failure leading to primary amenorrhoea (failure to establish menstruation by 16 years of age)
-Infertility
Diabetes
-Hypothyroidism (underactive thyroid gland)

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15
Q

Treatments of Turner’s Syndrome

A

-Incurable but treatments minimise symptoms (growth hormones, oestrogen replacement and multidisciplinary management/follow up)

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16
Q

Causes of Turner’s Syndrome

A
  • 80% of cases due to loss of X chromosome or Y chromosome in paternal meiosis)
  • 20% of cases due to other causes like single arm deletion, ring chromosome or mosaicism)
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17
Q

Clinical features of Klinefelter’s Syndrome

A
  • mild learning disability
  • taller than average (long lower limbs)
  • infertility
  • gynaecomastia (male breast tissue swells and becomes larger than normal)
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18
Q

Klinefelter Syndrome patients are at risk of?

A
  • leg ulcers
  • osteoporosis
  • breast carcinoma
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19
Q

Define congenital defect/abnormality/birth defect

A

Condition present from birth

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20
Q

Clinical features of Di George Syndrome

A

C=cardiac anomalies (interrupted aortic arch and the tetralogy of fallot)
-The tetralogy of fallot includes overriding aorta, pulmonary stenosis, right ventricular hypertrophy and ventricular septal defect
A=abnormal facies (low set ears, widely spaced eyes)
T=thymic hypoplasia
C=cleft palate
H=hypocalcaemia
2
2
-learning difficulties and difficulty feeding

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21
Q

Clinical features and prognosis of Charcot-Marie-Tooth disease type 1A

A
  • foot drop
  • distal muscle wasting
  • pes cavus (claw foot)
  • absent reflexes
  • lack of sensation in upper/lower limbs
  • slow nerve conduction velocity
  • incurable but treatment minimises symptoms with physiotherapy and corrective surgery
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22
Q

Define malformation

A

A morphological defect of an organ, part of an organ or a larger region of the body resulting from an intrinsically abnormal development process (primary structural defect of an organ/tissue)

  • single organ shows a multifactorial inheritance (many factors are involved in causing the birth defect, both genetic and environmental)
  • Abnormal developmental pathway from beginning
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23
Q

Define disruption

A
  • A morphological defect of an organ, part of an organ or a larger region of the body resulting in the extrinsic breakdown of, or interference with, an originally normal development process (secondary structural defect of an organ/tissue)
  • Normal development pathway is disrupted by an extrinsic factor giving an abnormal result
  • Irreversible
  • not caused by genetic factors but they can predispose
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24
Q

Define deformation

A
  • Abnormal form, shape or position of part of the body due to mechanical force (abnormal mechanical force distorts/disrupts the structure)
  • Potentially reversible
  • Change in development from normal to abnormal by mechanical force
  • Occurs late in pregnancy and has good prognosis as underlying structure is normal
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25
Q

Define dysplasia (congenital defect)

A
  • Abnormal organisation (disorganised layout) of cells into tissues and its morphological results
  • genetical cause
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26
Q

Define syndrome

A
  • Consistent pattern of abnormalities with a specific underlying cause
  • abnormalities are though to be pathogenetically related and not representing a sequence
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27
Q

Define association

A
  • Non random occurrence in two or more individuals of abnormalities not explained by syndrome and hence have an unknown cause (causality is not identified)
  • Also not known to be a polytopic defect (defects in one concentrated area of the body), sequence or syndrome
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28
Q

Define sequence

A
  • Pattern of multiple abnormalities initiated from a primary factor
  • primary factor is a single known or presumed prior anomaly or mechanical factor
  • one event leads onto another
  • the primary factor can be genetic
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29
Q

Give an example of malformation

A

-Aortic septal defect (abnormal hole in the septum between the two upper chambers of the heart)
-The aortic septal defect occurs at an early stage, will not be fixed by itself and will continue to grow/develop over time
Another example is cleft lip

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30
Q

Give an example of disruption

A
  • Amniotic band syndrome
  • The fibrous amniotic bands developed from the inner lining of the amniotic sac act as a tourniquet and wrap around the digits, restricting the blood flow and causing digital amputation or impediment of normal development
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31
Q

Give an example of deformation

A
  • Hip dislocation
  • Club foot (=talipes equinovarus,one or both feet point down and inwards)
  • Club foot can be reversed/straightened out through physiotherapy and in some cases, corrective surgery
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32
Q

Give an example of dysplasia

A

-Thanatophoric dysplasia (severe skeletal disorder)
-Thanatophoric dysplasia is characterised by a mutation in the single FGFR3 gene
-It is considered to be autosomal dominant
-infants with the disorder are often stillborn or die shortly after birth from respiratory failure
Clinical features include:
-Short limbs
-Large skull leading to an enlarged head
-Narrow thorax resulting in underdeveloped lungs
-folds of redundant skin on the arms and legs
-wide spaced eyes
-bowed long bones (in type 1)

33
Q

Give an example of syndrome

A

-Downs Syndrome due to a single extra copy of chromosome 21

34
Q

Give an example of association

A

-VACTERL association of birth defects affecting many body systems

35
Q

Give an example of sequence

A
  • Potter sequence
  • Primary factor is an abnormality in the urogenital tract (bilateral renal agenesis or urethral atresia)
  • Leads to reduced urine output and then oligohydramnios (decrease in the amount/low volume of amniotic fluid in the amniotic sac)
  • Secondary abnormalities then result=clubbed feet, pulmonary hypoplasia and potter facies (all have a common primary factor although effect is on different parts of the body)
36
Q

Cause of Di George Syndrome

A

Micro-deletion in chromosome 22 (loss of 30-50 genes including TBX1)

37
Q

Cause of Charcot-Marie-Tooth disease Type 1A

A

Micro-duplication in chromosome 17 (observe duplication of PMP22 during this)

38
Q

Effects of advanced maternal age on Down’s Syndrome risk

A
  • Strong association of increased syndrome risk with an increase in maternal age
  • Significant risk increase from mid 30’s onwards
39
Q

Incidence of Downs Syndrome at birth

A

Approx 1:700

40
Q

Survival time for Patau Syndrome

A

Patients rarely survive past 1 month

41
Q

Survival time for Edward’s Syndrome

A

Less severe compared to Patau’s, but the majority of patients still die within the first year of life

42
Q

TBX1

A

Gene coding for a transcription factor involved in the regulation of many developmental processes

43
Q

PMP22

A

Gene coding for an integral membrane protein which is a major component of myelin in the peripheral nervous system

44
Q

Define aneuploidy

A

The loss or gain of one or more chromosomes

45
Q

Monosomy X

A
  • Only viable monosomy

- Observed in Turner’s Syndrome

46
Q

Genotype of Klinefelter’s Syndrome

A

47, XXY

47
Q

Genotypes of the rare Klinefelter Syndrome variants

A

48, XXXY

49, XXXXY

48
Q

Characteristics of autosomal dominant

A
  • At least one affected parent
  • Transmitted from either parent (male or female)
  • Male and female offspring both affected
  • Vertical transmission as there is an affected family member in every generation
49
Q

Example of an autosomal dominant disease

A

Huntington’s Disease

50
Q

Define genetic anticipation

A

/

51
Q

Characteristics of autosomal recessive

A

/

52
Q

Example of an autosomal recessive disease

A

Cystic fibrosis

53
Q

Characteristics of X-linked recessive

A

/

54
Q

Example of an X-linked recessive disease

A

Haemophilia

55
Q

MELAS

A

Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes

56
Q

Symptoms of MELAS

A

/

57
Q

LHONS

A

Leber’s Hereditary Optic Neuropathy

58
Q

PKU

A

Phenylketonuria

59
Q

Clinical features of PKU

A
  • blond hair
  • blue eyes
  • musty odour from excess phenylacetate
  • light skin (lack of melanin)
  • eczema
60
Q

MCADD

A

Medium-chain Acyl-CoA dehydrogenase deficiency

61
Q

List the single congenital abnormalities

A

Malformation, disruption, deformation and dysplasia

62
Q

List the multiple congenital abnormalities

A

Syndrome, association and sequence

63
Q

Possible extrinsic factors causing disruption

A

Infection, mechanical trauma, ischaemia (common=inadequate blood supply to the tissues)

64
Q

Pulmonary hypoplasia in relation to Potters sequence

A

Incomplete development of the lung tissue

65
Q

Potter facies

A
  • flattened nose
  • low set abnormal ears
  • micrognathia (one or both jaws are unusually small)
  • epicanthal folds (vertical skin folds from the upper eyelid covering the inner corners of the eye)
66
Q

Disruption of a gene

A

When the breakpoint for translocation occurs in the middle of a gene, hence causing the functional deletion of that gene

67
Q

Ratio for newborns with significant congenital abnormalities

A

1:50

68
Q

Contribution of genetic factors to congenital abnormalities

A
  • Approximately 40%

- Vast majority of contribution to abnormalities are from other multiple factors

69
Q

Main difference between the multiple congenital abnormalities

A

Mechanism by which the clinical features/ symptoms are linked

70
Q

Proportion of deaths occurring during the perinatal period and in childhood up to 10 years of age

A
  • 20%-25% of all deaths

- congenital abnormalities are a large factor in terms of morbidity and mortality in the paediatric population

71
Q

Clinical features of Potter facies

A
  • abnormal ear lobation and low set
  • micrognathia (undersized jaw)
  • flattened nose
  • epicanthal folds
72
Q

Chromosomal set inherited from one parent

A
  • 22 autosomes and 1 sex chromosomes (X or Y depending on yours and parents gender)
  • haploid number were every chromosome is different (23)
73
Q

Point mutations

A

Missense and nonsense

-change in one DNA base pair resulting in the substitution of one amino acid in the polypeptide chain

74
Q

Missense mutation

A
  • single nucleotide is replaced at one point giving a single incorrect amino acid
  • may give a malfunctioning protein (not all the time)
75
Q

Silent mutation

A

/

76
Q

Nonsense mutation

A

/

77
Q

Frameshift mutations

A

Insertion and deletion

78
Q

Pedigree diagram features

A
  • square=male
  • circle=female
  • dot inside shape=carrier for recessive condition
  • sloping line from bottom left corner=person has died
  • filled in shape=affected by genetic disease
  • obtain details such as miscarriages, stillbirths, deaths etc for each partnership
  • miscarriages represented as smaller shape, filled in with number of miscarriages labelled underneath
  • ask if individual has children with other partners
  • proband=person who is the starting point of the family’s genetic study=first person to be treated for a genetic disorder in family
  • label with name (maiden name) and date of birth

MCD (13 decks)

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