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MBChB IV Paediatrics > Common genetic syndromes > Flashcards

Common genetic syndromes Flashcards

1
Q

Deformation

A

An abnormal mechanical force which distorts an otherwise normal structure

Eg mild talipes (club foot), plagiocephaly in twins

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2
Q

Disruption

A

An abnormal structure of an organ or tissue as a result of external factors disturbing the normal developmental process (ischemia, infection, trauma)

Eg amniotic band syndrome

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3
Q

Malformation

A

Primary structural defect of an organ which results from an inherent abnormality in development

Eg cleft palate, neural tube defect

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4
Q

Dysplasia

A

An abnormal organisation of cells into tissue in all parts of the body in which that particular tissue is present

Eg ectodermal dysplasia, skeletal dysplasia

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5
Q

Syndrome

A

Consistent patterns of abnormalities for which there is often a known underlying cause

Eg Down (chromosomal), Van Der Woude (single gene), Amniotic Band Syndrome (disruption)

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6
Q

Sequence

A

Consequence of a cascade of events initiated by a single primary factor

Eg Potter sequence, Pierre Robin sequence

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7
Q

Potter sequence

Pathophysiology

A

Renal agenesis/leaking of amniotic fluid -> oligohydramnios -> deformation due to pressure effects -> lung hypoplasia -> death

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8
Q

Pierre Robin sequence
Causes
Pathophysiology

A

Causes include collagen syndrome (stickler), generalised undergrowth of mandible, neurogenic hypotonia, oligohydramnios

Mandibular hypoplasia -> micrognathia -> retroglossoptosis -> U shaped cleft palate

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9
Q

Association

A

Certain malformations tend to occur together but are not explained by sequence or syndrome

Eg VACTERL

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10
Q

VACTERL

A 
Vertebral defects
Anus imperforatum
Cardiac defects
Tracheo-Esophageal fistula
Renal defect/retarded growth
Limb defects
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11
Q

What is the cause of dysplasia?

A

Single gene disorder

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12
Q

What is the cause of malformation?

A

Single gene disorder
Chromosome abnormality
Multifactorial disorder
Teratogen

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13
Q

What is the cause of disruption?

A

Teratogen

Abnormal uterine environment

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14
Q

What is the cause of deformation?

A

Abnormal uterine environment

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15
Q

Preconceptual causes of birth defects

A

Chromosomal
Single gene
Multifactorial

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16
Q

Postconceptual causes of birth defects

A

Drugs and chemicals
Infections
Maternal illness
Physical agents

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17
Q

Single gene disorders

A 
AD
AR
XD
XR
Other (mitochondrial)
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18
Q

Neurofibromatosis type 1

General

A

Autosomal dominant
1/3000
NF1 locus on chromosome 17 + gene cloned
Recurrence risk 50%

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19
Q

Neurofibromatosis type 1

Clinical features

A 
Cafe au lait patches more than 5 of 0.5cm-1.5cm
Neurofibroma
Lisch nodules
Intellectual disability
Seizures
Malignant changes
Learning disorders
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20
Q

Common AD conditions

A

NF1
Achondroplasia
Marfan syndrome
Huntington’s disease

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21
Q

Oculocutaneous albinism

General

A 
Autosomal recessive
Hereditary defect in metabolism of melanin -> decrease/abscence of pigment in the skin, mucosa, hair +/- eyes
P gene chromosome 15
OCA2 1/4000
Recurrence risk 25%
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22
Q

Oculocutaneous albinism

Clinical features

A 
Depigmented skin and hair
Skin sensitivity
Nystagmus
Retina depigmented
Visual problems
Increased skin cancer susceptibility
23
Q

Oculocutaneous albinism

Management

A

Limit skin sun exposure (protective clothing, sunscreen lotion, glasses)
Blind school
Suspicious skin lesions need attention
Dermatologist + ophthalmologist visits yearly
Genetic counselling

24
Q

Common AR conditions

A 
OCA
Spinal muscular atrophy
Thalassemia
Sickle cell disease
CF
IEM
25
Q

Duchenne muscular dystrophy

General

A 
XR
1/3500 
No ethnic variation
DMD gene on X.p21 dystrophin product
Carrier testing in females
Becker's MD is a milder phenotype
26
Q

Duchenne muscular dystrophy

Clinical features

A 
Muscle weakness 3/5yo
Positive Gower's sign
Delay in walking
Wheelchair bound by 11yo
Death at +/- 18yo
Pseudohypertrophy of calf muscles + wasting of proximal muscles
Mild to moderate intellectual impairment
Cardiac muscle involvement
27
Q

Common XR conditions

A

Duchenne muscular dystrophy
Hemophilia A/B
Fragile X syndrome

28
Q

X-linked dominant conditions

A

Rett syndrome

Goltz syndrome

29
Q

Mitochondrial conditions

A

Myopathy
Blindness
Deafness

30
Q

Imprinting disorders

A

Angelman syndrome

Prader-Willi syndrome

31
Q

Chromosomal disorders

Numerical abnormalities

A 
Down syndrome (46XY +21)
Patau syndrome (T13)
Edward syndrome (T18)
Turner syndrome (45X)
Klinefelter syndrome (47XXY)
32
Q

Chromosomal disorders

Structural abnormalities

A 
Balanced/unbalanced translocations
Deletions
Duplications
Inversions
Insertions
Ring chromosomes
33
Q

Down syndrome

General

A

Most common cause congenital mental disability in developed countries
1/600
Assoc with AMA >35yo

34
Q

Down syndrome

Types

A

Non-dysjunction 92%-95%
Translocation (5%)
Mosaic (3%)

35
Q

Down syndrome

Clinical features

A 
Small brachycephalic head
Third fontanelle
Increased nuchal skin
Facial dysmorphism
Open mouth
Protuberant tongue
Epicanthic folds
Upslanting palpebral features
Short stature
Prominent hypotonia 
Short stubby fingers
Single palmar crease
Clinodactyly
Sandal gap
Cardiac defects
Skeletal defects
GIT defects
Mental retardation
Increased haemotological + endocrine risk eg thyroid
36
Q

Down syndrome

Management

A 
Stimulation programs
Special schooling
Sheltered employment
Surgery for cardiac defects
Recurrent infections
37
Q

Down syndrome

Recurrence risk

A

Non-dysjunction 1% and increases with AMA
Translocation 10% if mother 2% if father
Mosaic <1%

38
Q

Down syndrome

Antenatal testing

A 
Maternal serum screening
Nuchal transparency on US
Chorionic villi sampling
Amniocentesis
Fetal DNA in maternal circulation (non-invasive prenatal)
39
Q

Edward syndrome

A

T18
>130 different noted abnormalities
Causes include non-dysunction, translocation, mosaicism, partial T18

40
Q

Turner syndrome

A

45X
1/2500 females
Most conceptuses die early
Most likely paternal X chromosome missing
Usually sporadic and AMA not significant
Does not cause mental deficiency - look for another defect

41
Q

Klinefelter syndrome

A

47XXY
1/500
Most common single cause for hypogonadism and infertility

42
Q

Multifactorial inheritance

Examples

A

Neural tube defects
Cleft lip/palate
Congenital cardiac defects
Diabetes, HT, other common disorders

43
Q

Neural tube defects

General

A

Multifactorial
Anencephaly/encephalocoele/spina bifida
Failure of neural tube to close by end of 4th week postconception
Genetic predisposition + folic acid deficiency (environment)

44
Q

Neural tube defects

Recurrence risk

A

1 affected child 5%
2 affected children 10%
1 parent affected 4%
Folic acid preconceptually reduces risk 72%

45
Q

Neural tube defects

Prenatal diagnosis

A

AFP on maternal and amniotic fluid

Maternal U/S

46
Q

Teratogen

A

A drug, chemical infectious or physical agent, maternal disease or metabolic agent that by acting on the developing fetus causes a structural or functional abnormality (congenital malformation or birth defect) present at birth

47
Q

Susceptible stages of development for teratogenesis

A 
0-17 days not susceptible
18-30 days highest susceptibility
31-60 days susceptibility continues
2nd trimester decreasing susceptibility
3rd trimester minimal susceptibility
48
Q

Foetal alcohol syndrome

Clinical presentation

A 
Growth deficiency:
Small stature
Microcephaly (mental deficiency, poor fine motor, hyperactivity)
Facial dysmorphism (short nose, micropthalmia, inner epicanthic folds, smooth philtrum, thin vermillion border, small midface)
Other (cardiac, skeletal defects)
49
Q

Foetal alcohol syndrome

Etiology

A 
Most common teratogen
Heavy alcohol exposure
Safe level unknown
Bingeing more harmful
Abstain!
50
Q

Teratogen examples

A 
Maternal disease
Maternal infection
Environmental chemicals
Radiation
Alcohol
Drugs
51
Q

Maternal diseases causing teratogenicity

A 
DM
Phenylketonuria
Epilepsy
Hyperthermia
Hyperthyroidism
Starvation
52
Q

Maternal infections causing teratogenicity

A 
Toxoplasmosis
Rubella
CMV
HSV
Syphilis
HVZ
Parvovirus
HIV
53
Q

Drugs causing teratogenicity

A 
Anticoagulants (warfarin)
Anticonvulsants (phenytoin)
Anticancer drugs 
Antibiotics (tetracycline)
Hormones (androgens, diethylstilbestrol)
Psychiatric drugs (lithium)
Vitamin A analogues (roaccutane)
Salicylates (aspirin)

MBChB IV Paediatrics (81 decks)

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