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Paediatrics > Genetics > Flashcards

Genetics Flashcards

1
Q

Name some autosomal dominant diseases.

A
  • Noonan syndrome
  • Neurofibromatosis type I
  • Tuberous sclerosis
  • Huntington’s disease
  • Myotonic dystrophy
  • Marfan syndrome
  • Ehlers-Danlos syndrome
  • Achondroplasia
  • Osteogenesis imperfecta
  • Autosomal dominant polycystic kidney disease
  • von Willebrand disease
  • Hereditary spherocytosis
  • Familial hypercholesterolemia
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2
Q

Name some autosomal recessive diseases.

A
  • Congenital adrenal hyperplasia
  • Cystic fibrosis
  • Sickle cell anemia
  • Thalassemia
  • Friedreich’s ataxia
  • Ataxia telangiectasia
  • Werdnig-Hoffmann disease (Type I)
  • Phenylketonuria
  • Glycogen storage diseases
  • Galactosemia
  • Mucopolysaccharidoses
  • Tay-Sachs disease
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3
Q

Name some X-linked recessive diseases.

A
  • G6PD deficiency
  • Hemophilia A and B
  • Wiskott-Aldrich Syndrome
  • Duchenne muscular dystrophy
  • Lesch-Nyhan syndrome (Fragile X syndrome)
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4
Q

What is the most common genetic cause of severe learning difficulties?

A

Down syndrome (47, T21)

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5
Q

What is the most common autosomal chromosomal abnormality?

A

Down syndrome (47, T21)

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6
Q

What is the incidence of Down syndrome?

A

1 in 650-800 - Increases with maternal age
>> 1 in 1500 in age 20
>> 1 in 20 in age 45

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7
Q

What are the features of Down syndrome on inspection?

A

Head

  • Microcephaly
  • Brachycephaly

Eyes

  • Upslanting palpebral fissures
  • Inner epicanthal folds
  • Speckled iris with Brushfield spots
  • Strabismus
  • Nystagmus

Ears
- Low-set and small ears

Face

  • Protruding tongue
  • Low and flat nasal bridge
  • Small nose

Hands

  • Transverse palmar (Simian) crease
  • Clinodactyly
  • Absent middle phalanx of the 5th finger

Toes
- Wide “sandal” gap between the big and second toe

Skeletal

  • Short stature
  • Excess nuchal skin (increased nuchal translucency)
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8
Q

What medical conditions are associated with Down Syndrome?

A

Eyes

  • Refractive errors
  • Acquired cataracts
  • Strabismus
  • Nystagmus

Ears

  • Recurrent acute otitis media due to horizontal Eustachian tube
  • Hearing loss

Skeletal
- Short stature
- Joint hyperflexibility
>> Hip dysplasia
>> Atlantoaxial instability
>> Vertebral anomalies

Cardiac
- Atrioventricular septal defect (50%)

Gastrointestinal

  • Duodenal atresia
  • Tracheoesophageal fistula
  • Hirschsprung’s disease

Genitourinary

  • Cryptorchidism
  • Infertility

Neurological

  • Intellectual impairment
  • Developmental delay
  • Hypotonia at birth
  • Alzheimer’s disease onset at 40 years

Hematological

  • Polycythemia
  • 1% lifetime risk of leukemia

Others
- Hypothyroidism

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9
Q

What are the possible causes of the extra chromosome in Down syndrome (T21)?

A

Meiotic non-disjunction (94%)

  • An error at meiosis
  • Related to maternal age

Translocation (5%)

  • Robertsonian translocation: when the extra chromosome 21 is jointed onto another chromosome (e.g. chr 14, 15, 22 or 21) – usually chromosome 14
  • Down syndrome with a set of 46 chromosomes but with three copies of chromosome 21 material

Mosaicism (1%)

  • Some cells are normal, and some have T21
  • After formation of a chromosomally normal zygote by non-disjunction at mitosis
  • Can arise by later mitotic nondisjunction in a T21 conception
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10
Q

What is the management for Down syndrome?

A

LONG-TERM!

  • Support for the child and parent
  • Genetic counseling
  • Recommended chromosomal analysis: confirm dx
  • Hearing test: hearing losses
  • Ophthalmology assessment: cataracts, refractive errors
  • Atlanto-occipital X-ray at 2 years: atlantoaxial instability
  • Echocardiogram: ASVD
  • CBC: polycythemia, increased risk of leukemia
  • Annual thyroid test: hypothyroidism
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11
Q

What is the most common sex chromosome disorder?

A

Turner syndrome (45XO)

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12
Q

What is the most common outcome of ALL CASES of Turner syndrome?

A

Early miscarriage

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13
Q

What is the relationship between maternal age and Down syndrome?

A

Significant increased risk in advanced maternal age Mother 20 years: 1 in 1500 Mother 45 years: 1 in 20

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14
Q

What is the relationship between maternal age and Turner syndrome?

A

Incidence does NOT increase with maternal age. The risk of recurrence is VERY LOW.

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15
Q

What are the clinical features of Turner syndrome?

A
  • Lower posterior headline
  • Short webbed neck
  • Cystic hygroma in newborn with polyhydramnios
  • Broad chest with widely spaced nipples
  • Lung hypoplasia
  • Coarctation of the aorta with biscuspid aortic valve
  • Renal abnormalities
  • Increased risk of hypertension
  • Lymphedema of the hands and/or feet
  • Wide carrying angle
  • Streak gonads with infertility
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16
Q

What is the prognosis of Turner Syndrome?

A

Normal life expectancy if no complications

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17
Q

What is the management for Turner syndrome?

A
  • GH therapy for short stature
  • Estrogen replacement for development of secondary characteristics at the time of puberty
  • Echocardiogram/ECG for cardiac malformations
    >> Coarcation of the aorta
    >> Bicuspid aortic valve
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18
Q

How common is Turner syndrome?

A

1 in 4000 live female births

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19
Q

How common is Klinefelter syndrome?

A

1 in 1000 live male births

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20
Q

What are the clinical features of Klinefelter syndrome?

A
  • Tall and slim
  • Long bones with unfused epiphyseal plates
  • Developmental delay/Intellectual subnormality
  • Eunuchoidism
  • Feminizing features: gynecomastia
  • Sterility: azoospermia, hypogonadism
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21
Q

What are the complications of Klinefelter syndrome?

A

Increased risk of germ cell tumours and breast cancer

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22
Q

What is the management of Klinefelter syndrome?

A

Testosterone in adolescence

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23
Q

What is the relationship between maternal age and Klinefelter syndrome?

A

Increased risk with advanced maternal age
>> Recurrence risk very low

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24
Q

What is the mode of inheritance of Noonan syndrome?

A

Autosomal dominant

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25
Q

How common in Noonan syndrome?

A

1 in 2000 female and male live births

26
Q

What are the clinical features of Noonan syndrome?

A

“Male Turner Syndrome” - although can occur in both females and males

>> Short stature
>> Webbed neck
>> Triangular facies
>> Hypertelorism (orbital)
>> Low set ears
>> Epicanthal folds
>> Ptosis
>> Moderate intellectual disability
>> Delayed puberty

  • Pectus excavatum
  • Right-sided congenital heart disease: Pulmonary stenosis
27
Q

What is the management for Noonan syndrome?

A
  • ECHO/ECG for cardiac abnormalities (PS)
  • Testosterone for affected males
28
Q

What is the mode of inheritance for Fragile X syndrome?

A

X-linked with genetic anticipation and mixed penetrance
(Recessive VS. dominant debatable)
>> CGG trinucleotide repeat on X-chromosome non-coding region

29
Q

What are the clinical features of Fragile X syndrome?

A

6Ms!

M: Mutation in FMR1 gene on X-chromosome
M: Mental retardation
M: Macrotia (large everted ears)
M: Macrognathia
M: Macro-orchidism
M: Mitral valve prolapse

+ Long and thin face
+ Hyperextensibility
+ High arched palate

30
Q

What are the complications of Fragile X Syndrome?

A
  • Mitral valve prolapse
  • Seizures
  • Scoliosis
  • Premature ovarian failure in females
  • Tremor/ataxia in males later in life
31
Q

What is the most common heritable cause of intellectual disability in boys?

A

Fragile X syndrome

32
Q

How common is Fragile X syndrome?

A

1 in 3600 males 1 in 6000 females

33
Q

How is Fragile X syndrome diagnosed?

A

Molecular testing of FMR1 gene

34
Q

What is the genetic cause of Prader-Willi Syndrome?

A

Deletion of paternal chromosome 15q11 or two maternal chromosomes 15q11

35
Q

What are the presenting features of Prader-Willi Syndrome?

A

H3O

  • Hypotonia and weakness
  • Hypogonadism
  • Hyperphagia
  • Obesity

+ Short stature
+ Almond-shaped eyes
+ Small hands and feet with tapering of fingers
+ Hypopigmentation
+ Type II DM

36
Q

What is the genetic cause of Angelman syndrome?

A

Maternally derived deletion of typically maternally expressed genes - paternal copy silenced epigenetically

37
Q

What are the presenting features of Angelman syndrome?

A
  • Severe mental retardation with ataxia
  • Uncontrollable laughter
  • Hypotonia
  • Seizures
  • Tremor
  • Midface hypoplasia
  • Fair hair

“Blonde laughing bimbo - high!”

38
Q

What is the most common genetic diagnosis?

A

Down syndrome

39
Q

What is the second most common genetic diagnosis?

A

DiGeorge syndrome

40
Q

What is the genetic cause of DiGeorge syndrome?

A

Microdeletion of chromosome region 22q11

41
Q

What are the presenting features of DiGeorge syndrome?

A

CATCH 22
C: Cardiac abnormalities - truncus, TOF
A: Abnormal facies - micrognathia, low-set ears
T: Thymic aplasia
C: Cleft palate/Cognitive impairment
H: Hypoparathyroidism, hypocalcemia
22: 22q11 microdeletions

42
Q

How common is Prader-Willi syndrome?

A

1 in 15000

43
Q

What is the genetic cause of Williams syndrome?

A

Sporadic mutation

44
Q

What are the clinical features of Williams syndrome?

A
  • Short stature
  • Characteristic facies
  • Transient neonatal hypercalcemia
  • Congenital heart disease: supravalvular aortic stenosis
  • Mild-moderate learning difficulties
45
Q

What are two common causes of lens subluxation?

A
  • Marfan syndrome
  • Homocystinuria
46
Q

What are the types of inborn errors of metabolism?

A

Carbohydrate

  • Galatosemia
  • Glycogen storage diseases

Proteins

  • Phenylketonuria
  • Tyrosemia
  • Homocystinuria
  • Organic acid disorders
  • Urea cycle disorders

Lipids
- Fatty acid oxidation defects

Organelle disorders

  • Congenital disorders of glycosylation
  • Mucopolysaccharidoses
47
Q

What is the underlying pathophysiology of galactosemia?

A

Galactose-1-phosphate uridyltransferase deficiency
>> Autosomal recessive
>> Inability to process lactose or galactose

48
Q

What are the presenting features of galactosemia?

A
  • Vomiting
  • Jaundice
  • Failure to thrive
  • Liver and renal failure
  • Cataracts
  • Developmental delay
    (+ Hypoglycemia)

>> Usually onset when lactose-containing milk feeds such as breast or infant formula are introduced

49
Q

What is the management of galactosemia?

A

Elimination of galactose and lactose from the diet
>> Soy-based diet

50
Q

What are some examples of glycogen storage diseases?

A

Muscle-predominant

  • Type II: Pompe’s disease – death by cardiomegaly/CHF
  • Type V: McArdle’s disease

Liver-predominant (hepatomegaly/hypoglycemia)

  • Type I: von Gierke’s disease
  • Type III: Cori’s disease (milder form of type I)

Type II and III can affect both liver and muscle.

51
Q

What are some long-term complications of von Gierke’s disease (type I glycogen storage disease)?

A
  • Hyperlipidemia
  • Hyperuricemia
  • Hepatic adenomas
  • Cardiovascular disease
52
Q

What are the types of metabolic diseases associated with hyperammonemia?

A
  • Organic acid disorders
  • Urea cycle disorders
  • Aminoaciduria
53
Q

What are some examples of lipid storage disorders?

A
  • Tay-Sachs disease
  • Gaucher disease
  • Niemann-Pick disease
54
Q

What is the mode of inheritance of Tay-Sachs disease?

A

Autosomal recessive

55
Q

What are the clinical features of Tay-Sachs disease?

A
  • Developmental regression in late infancy
  • Severe hypotonia
  • Enlarging head
  • CHERRY RED SPOT ON MACULA
  • Death by 2-5 years
56
Q

What are the clinical features of Gaucher disease?

A
  1. Chronic childhood form
    - Splenomegaly
    - Bone marrow suppression
    - Bone involvement
    - Normal IQ
  2. Acute infantile form
    - Splenomegaly
    - Neurological degeneration with seizures
57
Q

What are the clinical features of Niemann-Pick disease?

A

Onset at 3-4 months of age

  • Feeding difficulties and FTT
  • Hepatosplenomegaly
  • Developmental delay
  • Hypotonia
  • Hearing and visual deterioration
  • Cherry red spot in macula in 50% (ddx: Tay-Sachs disease)
  • Death by four years
58
Q

What are mucopolysaccharidoses?

A

Progressive multi-system disorders of lysosomal storage affecting:

  • Neurological
  • Ocular
  • Cardiac
  • Skeletal

Characterized by certain enzyme defects and URINE EXCRETION OF GAGs (glycosaminoglycans), the major storage substances

59
Q

What are the clinical features of mucopolysaccharidoses?

A

Developmental delay following a period of essentially normal growth and development: UP TO 6-12 MONTHS OF AGE

Other neurological

  • Carpal tunnel syndrome
  • Conductive hearing loss

Ocular

  • Corneal clouding
  • Retinal degeneration
  • Glaucoma

Cardiac

  • Valvular lesions
  • Heart failure

Abdomen

  • Hepatomegaly
  • Splenomegaly
  • Umbilical and inguinal hernias

Skeletal

  • Thickened skull
  • Broad ribs
  • Claw hand
  • Thoracic kyphosis
  • Lumbar lordosis

Skin

  • Thickened skin
  • Coarse facies
60
Q

What are some types of mucopolysaccharidoses?

A

MPS I: Hurler
MPS II: Hunter
MPS III: Sanfilippo
MPS IV: Morquio
MPS IV: Maroteaux-Lamy

61
Q

What are some examples of mineral storage disorders?

A
  • Wilson’s disease (copper)
  • Hemosiderosis (iron)

Paediatrics (16 decks)

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