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1 - Paeds AE > Genetics > Flashcards

Genetics Flashcards

1
Q

What are the down syndrome features present at birth?

A 
Typical facial appearance
Hypotonic
Flat occiput
Single palmar creases
Incurved fifth finger
Wide 'sandal' gap between the big and second toe
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2
Q

What is the typical craniofacial appearance in down syndrome?

A

Round face and flat nasal bridge
Upslanted palpebral fissures
Epicanthic folds (a fold of skin running across the inner edge of the palpebral fissure)
Brushfield spots in iris (pigmented spots)
Small mouth and protruding tongue
Small ears
Flat occiput and third fontanelle

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3
Q

What are the anomalies associated with down syndrome that don’t involve the typical craniofacial appearance?

A 
Short neck
Single palmar creases
Incurved fifth finger
Wide 'sandal' gap between toes
Hypotonia
Congenital heart defects (AV canal defect)
Duodenal atresia
Hirschsprung disease
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4
Q

What are the long-term medical problems associated with downs syndrome?

A

Delayed motor milestones
Moderate to severe learning difficulties
Small stature
Increased susceptibility to infection
Hearing impairment from secretory otitis media
Visual impairment from cataracts, squints, myopia
Increased risk of leukaemia and solid tumours
Risk of atlanto-axial instability
Increased risk of hypothyroidism and coeliac disease
Epilepsy
Alzheimer’s disease

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5
Q

What is the main cytogenetic cause of down syndrome?

A

Meiotic non-disjunction

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6
Q

What are some other chromosomal abnormalities apart from down syndrome?

A

Edwards syndrome
Patau syndrome
Turner syndrome

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7
Q

What are the clinical features of Edwards syndrome?

A 
Low birthweight
Prominent occiput
Small mouth and chin
Short sternum
Flexed, overlapping fingers
'Rocker-bottom' feet
Cardiac and renal malformations
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8
Q

What are the clinical features of Patau syndrome?

A 
Structural defect of brain
Scalp defects
Small eyes (microphthalmia and other eye defects)
Cleft lip and palate
Polydactyly
Cardiac and renal malformations
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9
Q

What are the clinical features of Turner syndrome?

A 
Lymphoedema of hands and feet in neonate, which may persist
Spoon-shaped nails
Short stature - a cardinal feature
Neck webbing or thick neck
Wide carrying angle (cubitus valgus)
Widely spaced nipples
Congenital heart defects (coarctation of the aorta)
Infertility
Hypothyroidism
Renal anomalies
Pigmented moles
Recurrent otitis media
Delayed puberty
Normal intellect function in most
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10
Q

How do you treat Turners syndrome?

A

Growth hormone therapy

Oestrogen replacement for development of secondary sexual characteristics at the time of puberty

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11
Q

What are the clinical features of Klinefelter syndrome?

A 
Infertility
Hypogonadism with small testes
Pubertal development may appear normal
Gynaecomastia in adolescence
Tall stature
Intelligence usually in the normal range, but some have educational and psychological problems
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12
Q

What is Mendelian inheritance?

A

The transmission of inherited traits or diseases caused by variation in a single gene in a characteristic pattern.

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13
Q

What are some examples of autosomal dominant disorders?

A 
Ehlers-Danlos syndrome
Familial hypercholesterolaemia
Huntington disease
Marfan syndrome
Myotonic dystrophy
Neurofibromatosis
Osteogenesis imperfects
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14
Q

What is the most common mode of Mendelian inheritance?

A

Autosomal dominant

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15
Q

Chromosomally, how would you summarise autosomal dominant inheritance?

A

Affected individual carries the abnormal gene on one of a pair of autosomes

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16
Q

What are the chances of inheriting the abnormal gene from an affected parent in autosomal dominant inheritance?

A

1 in 2 chance, 50%. But there may be variation in expression (severity), non-penetrance, no family history (new mutation, parental mosaicism, non-paternity)

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17
Q

What is non-penetrance?

A

It refers to the lack of clinical signs and symptoms in an individual who has inherited the abnormal gene.

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18
Q

What is parental mosaicism?

A

A healthy parent harbours the mutation only in some of their cells e.g. in their gonads

19
Q

What are some examples of autosomal recessive disorders?

A 
Congenital adrenal hyperplasia
Cystic fibrosis
Freidreich ataxia
Sickle cell disease
Thalassaemia
20
Q

Chromosomally, how would you summarise autosomal recessive inheritance?

A

Affected individuals are homozygous for the abnormal gene, each unaffected parent will be a heterozygous carrier

21
Q

What is the risk of two carrier parents having an affected child in an autosomal recessive disease?

A

1 in 4 risk. Risk of these disorders is increased by consanguity and within specific populations

22
Q

What sort of pathways do autosomal recessive disorders usually affect?

A

Autosomal recessive disorders often affect metabolic pathways, whereas autosomal dominant disorders often affect structural proteins

23
Q

How does X-linked recessive inheritance affect males and females?

A

Males are affected.

Females can be carriers but are usually healthy or have mild disease

24
Q

How would offspring be affected in an X-linked recessive disorder?

A

Each son of a female carrier had a 50% risk of being affected.
Each daughter of a female carrier has a 50% risk of being a carrier.
Daughters of affected males will all be carriers
Sons of affected males will not be affected.

25
Q

What are trinucleotide repeat expansion mutations?

A

A class of unstable mutations caused by unstable expansions of trinucleotide repeat sequences inherited in Mendelian fashion.

26
Q

What are some examples of trinucleotide repeat expansion mutations?

A

Fragile X syndrome
Myotonic dystrophy
Huntington’s disease
Friedrich’s ataxia

27
Q

What are the clinical features of Fragile X syndrome?

A

Moderate-severe learning difficulty
Macrocephaly
Macro-orchidism - post pubertal
Characteristic facies (long face, large everted ear, prominent mandible and broad forehead, most evident in affected adults)
Other features - mitral valve prolapse, joint laxity, scoliosis, autism, hyperactivity

28
Q

What are some examples of X-linked recessive disorders?

A

Colour blindness
Duchenne and Becker muscular dystrophy
Fragile X syndrome

29
Q

Why do mitochondrial disorders present in variable fashion?

A

The mutation may be present in all or only some of the mitochondria, so that the tissues affected and the severity of the condition can be highly variable

30
Q

What is imprinting?

A

It has been shown that the expression of some genes is influenced by the sex of the parent who has transmitted it. This phenomenon is called ‘imprinting’. An example is Prader-Willi syndrome

31
Q

What is a malformation?

A

A primary structural defect occurring during the development of a tissue or organ, e.g. spina bifida, cleft lip and palate

32
Q

What is a deformation?

A

Implies an abnormal intrauterine mechanical force that distorts a normally formed structure, e.g. joint contractures or pulmonary hypoplasia due to fetal compression caused by severe oligohydramnios.

33
Q

What is a disruption?

A

Involves destruction of a fetal part which initially form normally e.g. amniotic membrane rupture may lead to amniotic bands which cause limb reduction defects

34
Q

What is a dysplasia?

A

Refers to abnormal cellular organisation or function of specific tissue types e.g. skeletal dysplasia, dysplastic kidney disease

35
Q

What is a single-system defect?

A

Single congenital malformations, such as spina bifida, which are often multifactorial in nature with fairly low recurrence rates

36
Q

What are some pathogenic mechanisms?

A

Malformation
Deformation
Disruption
Dysplasia

37
Q

What are some clinical classifications of birth defects?

A

Single-system defects
Sequence
Association
Syndrome

38
Q

What is a sequence?

A

A pattern of multiple abnormalities occurring after one initiating defect.

39
Q

What is an association?

A

A group of malformations that occur together more often than expected by chance, but in difference combinations from case to case.

40
Q

What is a syndrome?

A

A particular set of multiple anomalies occurs repeatedly in a consistent pattern and there is known or thought to be a common underlying causal mechanism.

41
Q

What are some reasons for performing a genetic investigation?

A

Confirmation of clinical diagnosis
Detection of female carriers in X-linked disorders
Carrier detection in autosomal recessive disorders
Presymptomatic diagnosis in autosomal dominant disorders
Antenatal diagnosis of an increasing number of Mendelian conditions

42
Q

What are the main aims of genetic counselling for the parents?

A

To understand their situation
To make their own decisions about managing the disease or risk of disease
To adjust to their situation of being affected by or at risk of the condition

43
Q

What are the influences on decisions regarding options for genetic counselling?

A

Magnitude of risk
Perceived severity of disorder
Availability of treatment
Person’s experience of the disorder
Family size
Availability of a safe or reliable prenatal diagnostic test
Parental cultural, religious or ethical values

44
Q

When should pre-symptomatic testing not be given?

A

It should not be performed until the individual can give informed consent

1 - Paeds AE (24 decks)

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