Genetic Abnormalities of Head and Neck Development

Question 1

Describe Trisomy 21 - Downs Syndrome

Answer 1

• Mental retardation
• Characteristic facial features
• Lower life expectancy
• Risk for baby increases with age of mother
• Translocation Down Syndrome:
  1) Only inheritable version of Downs syndrome
  2) Chromosome 21 is attached to another chromosome

Question 2

Describe Trisomy 18 - Edward Syndrome

Answer 2

• Small heads with prominent occiput
• Mis-position of ears
• Small size of mouth and jaw
• Very short sternum
• Often suffer from cleft lip and palate

Question 3

Describe Trisomy 13

Answer 3

• Small head with sloping forehead
• Major structural brain problems: Failure for frontal brain to divide, leads to close set eyes and underdeveloped nose
• Cleft lip and palate in 80%
• Extra fingers

Question 4

Describe ‘deletion - cri du chat’

Answer 4

• Deletion of part of chromosome 5
• high pitch cry
• Small head size

Question 5

Describe ‘duplication - Pallister Killian’s syndrome’

Answer 5

• Extra chromosome 12 material added to chromosome 12
• Coarse facial features
• very thin upper lip
• very thick lower lip

Question 6

Define ‘ring’ in structural abnormalities

Answer 6

Chromosome ends join together

Question 7

Define ‘ inversion’ in structural abnormalities

Answer 7

Segment break, turn upside down then reattaches to same chromosome

Question 8

Define ‘reciprocal translocation’ in structural abnormalities

Answer 8

Two chromosome swap material

Question 9

Define ‘Robertsonian translocation’

Answer 9

Two chromosome ends break off, and fuse to form a new chromosome

Question 10

Define ‘translocation down syndrome’

Answer 10

Extra chromosome 21 is attached to another chromosome; inheritable Downs syndrome

Question 11

Describe Treacher-collins syndrome

Answer 11

• Autosomal dominant
• Can be due to environmental exposure in utero (e.g. alcohol)
• Major defects to mandible, lower lip and external ear

Question 12

Define Pierre Robin Sequence

Answer 12

• Small mandible growth
• Leads to posteriorly placed tongue
• Leads to cleft soft palate

Question 13

Describe DiGeorge Sequence

Answer 13

• Absence of thymus and parathyroid cells
• Abnormal external ears
• Small mandible

Question 14

Describe Goldenhar Syndrome

Answer 14

• Craniofacial abnormalities in maxillary, temporal, and zygomatic bones
• No teeth, tumour in eyes
• Mis-formed ear

Question 15

List three disorders caused by FGFR2 gene mutation

Answer 15

• Crouzon syndrome
• Apert Syndrome
• Pfeifer Syndrome

Question 16

List syndromes caused by disorders in development signals

Answer 16

• Premature joining of cranial bones
• Maxillary hypoplasia
• Dental problems

Question 17

Describe syndromic hypodontia

Answer 17

• Missing teeth

- Most common clefting syndrome

Question 18

Describe Gardner Syndrome

Answer 18

• Maxillary bone protuberances

- Causes tooth malformations

Question 19

Describe cleft lip/palate

Answer 19

• Signalling genes associated

- Hypodontia is most common trait associated with clefting

Question 20

Describe Amelogenesis imperfecta

Answer 20

• Mixed modes of inheritance (dominant, recessive, X-linked)
• Defects of enamel proteins (secreted by ameloblasts):
  1) Amelogenin (90%)
  2) Ameloblastin
  3) Enamelin
  4) Enamelysin

Question 21

Describe Dentinogenesis imperfecta

Answer 21

Defect in non-collagen proteins

• Dentin matrix protein1 (DMP1)
• Dentin sialoprotein (DSP)
• Dentin phosphoprotein (DPP)