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Flashcards in Genetics Deck (39):
1

Incidence of Down Syndrome in live births

1 in 650

2

Signs of Down Syndrome x7

Facies, hypotonic, flat occiput, short neck, single palmar creases, incurved 5th finger, wide 'sandal' gap between big and second toe

3

Heart disease in Down Syndrome

Congenital heart disease in 30%
Atrioventricular septal defect is a major cause of early mortality

4

Later medical problems with Down Syndrome x6

Delayed motor milestones
Learning difficulties
Short stature
Increased susceptibility to infection
Hearing impairment
Visual impairment

5

Why hearing impairment in Downs Syndrome?

Due to secretory otitis media

6

Disease risks with down syndrome x5

Increased risk of leukaemia and solid tumours
Increased risk of hypothyroidism
Coeliac disease
Epilepsy
Alzheimer's Disease

7

What is Edwards Syndrome? Incidence

Trisomy 18, 1 in 8000 live births
Micrognathia
Low-set ears
Rocker bottom feet
Overlapping fingers

8

What is Patau Syndrome? Incidence

Trisomy 13, 1 in 14,000 live births
Microcephalic
Small eyes
Cleft lip/palate
Polydactyly
Scalp lesions

9

Features of Patau and Edwards

Very severe mental and physical disabilities
Majority of affected babies die in infancy

10

What is 45, XO, incidence

Turner syndrome, 1 in 2500 of live born females

11

Consequence of Turner syndrome

>95% result in early miscarriage

12

Features of Turner Syndrome x11

Short stature (may be only feature)
Spoon-shaped nails
Neck webbing
Wide carrying angle (cubitus valgus)
Delayed puberty
Infertility due to ovarian dysgenesis
Hypothyroid
Renal abnormalities
Lymphoedema of hands and feet in neonate which may persist
Congenital heart defects
Recurrent otitis media

13

Treatment of Turner Syndrome x2

Growth hormone therapy - can counter short stature
Oestrogen replacement for development of secondary sexual characteristics at time of puberty

14

What is 47, XXY, incidence

Klinefelter Syndrome
1-2/1000 live born males

15

Features of Klinefelter x5

Infertility (most common presentation)
Hypogonadism
Gynaecomastia
Tall stature
May have some educational and psychological problems but intelligence usually normal

16

What increases incidence of autosomal recessive disorders

Consanguinity
Arab cultures this is more common

17

Disorders which have trinucleotide repeat expansion mutations x5

Fragile X
Myotonic dystrophy
Huntingtons disease
Spinocerebellar ataxia
Friedreichs ataxia

18

X-linked dominant inheritance disease

Hypophosphatemic (vitamin D-resistant) rickets

19

What is Fragile X Syndrome? Incidence

Significant learning difficulties in males, x-linked recessive but also trinucleotide expansion
Incidence 1 in 4000

20

Females and fragile x

Female carriers can have mild learning difficulties

21

Number of repeats needed for symptoms in Fragile X

CGG trinucleotide needs more than 200 copies of repeat - this is caused by gene with full mutation

22

Other clinical features of Fragile X in males

Macrocephaly
Macro-orchidism post puberty
Strabismus
Long face, large everted ears, prominent mandible and broad forehead
Mitral valve prolapse, joint laxity, scoliosis, autism and hyperactivity

23

Syndromes involving imprinting

Prader-Willi syndrome - absence of functional paternal copy of region will develop PWS
Angelman - failure to inherit functional maternal copy leads to this rather than PWS
Same region

24

Features of PWS x4

Hypotonia
Developmental delay
Hyperphagia
Obesity
Hypogonadism

25

Features of Angelman syndrome x4

Severe cognitive impairment
Characteristic facial impairment
Ataxia
Epilepsy

26

Definition of malformation

Primary structural abnormality occurring during development of tissue or organ

27

Definition of deformation

Abnormal intrauterine mechanical force that distorts a normally formed structure - eg. due to oligohydramnios

28

Definition of disruption

Destruction of fetal part which initially formed normally eg. amniotic membrane rupture may lead to amniotic bands which may cause limb reduction defects

29

Definition of dysplasia

Abnormal cellular organisation or function of specific tissue types
eg. skeletal dysplasias

30

What are single-system defects?

Single congenital malformations eg. spina bifida - which are often multifactorial in nature with fairly low recurrence risks

31

What are sequence birth defects?

A pattern of multiple abnormalities occurring after one initiating defect
eg. Potter syndrome following from oligohydramnios

32

What are association birth defects?

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

33

What are syndrome birth defects?

A particular set of multiple anomalies occurs repeatedly in a consistent pattern - common underlying causal mechanism

34

Craniofacial appearance in Down's syndrome

Round face
Flat nasal bridge
Upslanted palpebral fissure
Epicanthic folds
Brushfield spots in iris
Small mouth and protruding tongue
Small ears
Flat occiput and third fontanelle

35

GIT abnormalities in down syndrome

Duodenal atresia
Hirschsprungs disease

36

Intellectual ability in Turners

Normal usually

37

Features of Noonan syndrome

Webbed neck
Pectus excavatum
Short stature
Pulmonary stenosis (Congenital heart defects)

38

Features of Pierre-Robin syndrome

Micrognathia
Posterior displacement of the tongue (can cause upper airway obstruction)
Cleft palate

39

Features of William's syndrome

Short stature
Learning difficulties
Friendly, extrovert (highly verbal despite low IQ)
Transient neonatal hypercalcaemia
Supravalvular aortic stenosis