Medical Genetics

Question 1

What type of inheritance is shown here?

Answer 1

X-linked recessive.

Question 2

What is germline mosaicism?

Answer 2

Germline mosaicism, also called gonadal mosaicism, is a type of genetic mosaicism where more than one set of genetic information is found specifically within the gamete cells; conversely, somatic mosaicism is a type of genetic mosaicism found in somatic cells.

Question 3

What type of inheritance is shown here?

Answer 3

Autosomal recessive

Question 4

Haemophillia A affects clotting due to what deficiency?

Answer 4

Factor VIII deficiency

Question 5

List of X-linked conditions:

Answer 5

• Haemophilia A (Factor VIII deficiency)
• Red-green colour blindness
• Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy BMD)
• Fragile X syndrome
• Fabry’s disease, OTC deficiency
• Alport’s hereditary nephropathy

Question 6

List of Autosomal Dominant conditions:

Answer 6

• Marfan’s syndrome, achondroplasia
• Tuberous sclerosis
• Neurofibromatosis NFI, NF2
• Adult polycystic kidney disease (APKD)
• Huntington’s disease
• Myotonic dystrophy
• HMSNs, Charcot-Marie-Tooth disease
• Spino-cerebellar ataxias (SCAs)
• Hereditary cancer syndromes, BRCA1/2, HNPCC, FAP

Question 7

List of Autosomal recessive conditions:

Answer 7

• Cystic fibrosis
• Sickle cell, thalassaemia
• Haemochromatosis, -1-anti-trypsin deficiency
• Spinal muscular atrophy, (SMA)
• Infantile poly cystic kidney disease
• Congenital adrenal hyperplasia, (CAH) due to 21-OHase deficiency
• Inborn errors of metabolism e.g. PKU, storage disorders, e.g., MPS, Tay-Sachs

Question 8

What is the name of the tendency for a condition to have an earlier age of onset and progress more rapidly from one generation to the next?

Answer 8

Anticipation

Question 9

What is the molecular genetic mechanism responsible for anticipation?

Answer 9

Tri-nucleotide repeats

Question 10

Explain penetrance.

Answer 10

Penetrance in genetics is the proportion of individuals carrying a particular variant of a gene that also express an associated trait. In medical genetics, the penetrance of a disease-causing mutation is the proportion of individuals with the mutation who exhibit clinical symptoms.

Question 11

Explain incomplete penetrance.

Answer 11

Where you have the genotype but do not display clinical symptoms in your phenotype.