Genetic counselling in single gene disorders

Question 1

Genetic counseling is

Answer 1

the process of helping people understand and adapt to the medical, psychological and familial implications of genetic contributions to disease.

Question 2

This process integrates the following:

Answer 2

• Interpretation of family and medical histories to assess the chance of disease occurrence or recurrence.
• Education about inheritance, testing, management, prevention, resources and research.
• Counseling to promote informed choices and adaptation to the risk or condition.

Question 3

Newborn screening programme - in terms of CF

Answer 3

• Basedonheel-prickimmuno-reactivetrypsinogen (IRT) level
• Raised IRT - test using CF mutation kit
• CF suspected if IRT raised and one pathogenic
mutation found
• CF confirmed if 2 pathogenic mutations found

Question 4

R117H - a “mild” mutation

Answer 4

• The majority of R117H compound heterozygotes do not present with CF in childhood
• Effect of R117H varies according to Intron 8 splice site efficiency

Question 5

Spinal Muscular Atrophy (Werdnig-Hoffmann Disease)

Answer 5

• Progressive muscle weakness from degeneration of anterior horn cells
• Autosomal recessive
• 95% cases due to deletion of SMN1 (survival
motor neurone 1)

Question 6

Meckel Gruber syndrome

Answer 6

• variable phenotype
• autosomal recessive
• at least 6 genes

Question 7

biological dementia

Answer 7

• Substitution mutation in exon 7 of PSEN-1 gene changing codon 214 from CAC to TAC
• Replaces histidine with tyrosine in the PSEN-1 protein
• missense