[C] 1.66 Causes of developmental anomalies (formal and causal genesis)

Question 1

Developmental anomaly: Congenital anomaly

Answer 1

“Birth defect”

• Disorder present at birth
• Result of an inherited gene mutation
• Error during morphogenesis or foetal development

Question 2

Developmental anomaly: Physical anomaly

Answer 2

Deformation of an anatomical structure

Question 3

Major steps of morphogenesis

Answer 3

Question 4

Causes of maldevelopments “Causal genesis”

Answer 4

• Genetic origin
  
  • Single mutant genes of large effect
  • Multifactorial inheritance
  • Abnormalities of chromosomal structure
• Non-genetic origin

Question 5

Causes of maldevelopments: Genetic origin

Answer 5

• Inherited
• Chromosome mutations

Question 6

Causes of maldevelopments: Non-genetic origin

Answer 6

• Prenatal viral, bacterial, parasitic infection
  
  • Panleukemia, BVD
• Intrauterine exposure to poisons
  
  • Thalidomide, molybdenum, toxic plants
  • Timing of the effect is more important than the effector

Question 7

Causes of maldevelopments: Single mutant genes

Answer 7

• Mendelian disorders
• No abnormal chromosomal structures
• Inborn errors of metabolism

Question 8

Causes of maldevelopments: Multifactorial inheritance

Answer 8

• Additive effect of many genes with small impact
• No abnormal chromosomal structures
• Predisposing environmental influences

Question 9

Causes of maldevelopments: Abnormalities of chromosomal structure

Answer 9

• Abnormal number of chromosomes

Question 10

Proteins as mutant gene products

Answer 10

• Missing enzymes
  
  • Accumulation of precursors
    
    • Lipid storage disease
    • Mucopolysaccharidosis - Siamese cat
    • Glycogen storage diseases
  • Deficiency of end products
    
    • Albinism
  • Accumulation of toxic byproducts
    
    • Phenylketonuria

Question 11

Multifactorial inheritance disorders

Answer 11

• Polydactyly (Simmental cattle)
• Porcine encephalocele

Multiple defects transmitted together:

• Cyclic hematopoiesis in grey collies
  
  • Mainly neutrophils disappear in 11 day cycles
  • Abnormal grey silver colour
  • Microphthalmia

Question 12

Chromosomal defects: Abnormal chromosomal numbers

Answer 12

• Trisomy 17 in cattle
  
  • Brachygnathia
• Trisomy 21 in humans
  
  • Downs syndrome
• XO monosomy in horses
  
  • Turner syndrome in humans, pig, cats, sheep
• XXY males
  
  • Klinefelter’s syndrome in human
  • Tortoiseshell male cats

Question 13

Developmental anomalies: Virus induced congenital lesions

Answer 13

• Parvovirus
  
  • Kitten - Cerebellar hypoplasia
• Influenza virus
  
  • Chicken - Microencephaly
• BVD
  
  • Calves - Cerebellar hypoplasia
• Swine fever virus & border disease virus
  
  • Piglets & lambs - Cerebellar hypoplasia
• Atypical porcine pestivirus
  
  • Congenital tremor