x-linked pattern

Question 1

What is the manifestation of Duchenne Muscular Dystrophy?

Answer 1

Enlarged calves and wasting of the thigh muscle

For men, tends to be lethal before age of 30

Question 2

Duchenne muscular dystrophy has high or low reproductive fitness

Answer 2

Low

Question 3

Difference between Duchenne and Becker muscular dystrophy

Answer 3

Less severe mutation in DMD leads to Becker

More severe mutation in DMD leads to Duchenne

Question 4

When a child is affected, look for the disorder in maternal relatives. Which mode of transmission is this?

Answer 4

X-linked recessive

Question 5

What is manefestation of hemophilia A

Answer 5

inherent deficiency of clotting factor 8, resulting in increased tendency to bleed

Question 6

Relationship between hemophilia A and allelic heterogeneity

Answer 6

Inversion of intron lead to incorrect splicing

while other mutation leads to hemophilia A

Question 7

How is Duchenne muscular dystrophy transmitted?

Answer 7

X-linked recessive

Question 8

How is Hemophilia A transmitted?

Answer 8

X-linked recessive

Question 9

What causes X-linked SCID and what is the manifestation?

Answer 9

Due to defect in SCIDX1 gene, it leads to defect in gamma chain of receptor for several interleukins(IL2RG), which result into immature T-cell. This results in a deficiency of normal B-cell function.

Question 10

What happens if a woman who is carrier of Duchenne have a symptoms? How can it be explained?

Answer 10

It is due to skewed X-inactivation. The number of cells that contain the active X chromosome with the mutation in DMD are larger than cells that contain the active X with functional DMD gene.

Question 11

How is red/green color deficiency transmitted?

Answer 11

X-linked recessive

Question 12

How is Rett syndrome transmitted?

Answer 12

X-linked dominant

Question 13

What mostly happens to males who have X-linked dominant disorder?

Answer 13

Die in utero

Question 14

What is Rett syndrome?

Answer 14

Genetic brain disorder

Question 15

Manifestation of incontinentia pigmenti

Answer 15

rashes and blisters in early life and later, patches of hyperpigmentation

Question 16

How is incontinentia pigmenti trasmitted?

Answer 16

X-linked dominant

Question 17

Transmission of vitamin D resistant Rickets

Answer 17

X-linked dominant

Question 18

How can it be explained if a person who have inherited the mutant allele of autosomal dominant disorder does not display the disease phenotype?

Answer 18

A disorder is non-penetrance

Question 19

What incomplete penetrance?

Answer 19

Penetrance may be dependent on age, (adult onset disease),

Question 20

How do we calculate recurrence risk based on penetrance of 80% for autosomal dominant disease?

Answer 20

recurrence risk normal is 50%, so 50*80 / 100 = 40%.

So recurrence risk is 40% when penetrance is 80%

Question 21

What does variable expression mean?

Answer 21

severity of genetic disease is different due to some factors

Question 22

What are 3 factors affecting variable expression

Answer 22

1. Random chance
2. Other genetic factors or sex influence
3. Environmental exposure

Question 23

How is variable expression related to Hemochromatosis?

Answer 23

It is more severe in male , and premenapausal females will menstruate and lose iron.

Question 24

What is hemochromatosis and mode of transmission?

Answer 24

an iron overload disorder (autosomal recessive)

Question 25

What is xeroderma pigmentosum and mode of transmission?

Answer 25

Decreased ability to repair DNA damage caused by UV rays (autosomal recessive)

Question 26

Explain Neurofibromatosis type I in terms of penetrance and variable expression

Answer 26

All patients with the mutant NF1 gene express at least some signs of the disorder (High penetrance), but severity is different (variable expression)

Question 27

What is pleiotropy

Answer 27

A disease causing mutation affects more than one organ system

Question 28

What is pleiotropy

Answer 28

A disease causing mutation affects more than one organ system

Question 29

What is cause and manifestation of marfan syndrome?

Answer 29

due to mutation in fibrillin-1 gene, skeletal abnormalities (long limb), hypermobile joints, ocular abnormalities, cardiovascular disease

Question 30

How is marfan syndrome transmitted?

Answer 30

Autosomal dominant

Question 31

cause and manifestation of osteogenesis imperfecta

Answer 31

brittle bones, blue sclera due to mutation in gene encoding pro-collagen

Question 32

Example of disease that shows pleiotropy

Answer 32

Marfan syndrome, osteogenesis imperfecta

Question 33

What is locus heterogeneity?

Answer 33

Mutation at different loci or gene cause same disease phenotype.

Question 34

Example of disease that show locus heterogeneity

Answer 34

Osteogenesis imperfecta (mutation in chromosome 7 and 17 shows defect in collagen
Breast cancer (mutation in BRCA1 &2, cause increased predisposition to breast cancer)

Question 35

Example of autosomal recessive inheritance + locus heterogeneity

Answer 35

Congenital deafness

Question 36

pathology of CF

Answer 36

Lung : mucus in lung is very viscous and is not cleared from lung or airway causing recurrent infection and inflammation leading to tissue damage.

Pancrea : pancreatic duct gets clogged because of viscous mucus, leading pancreatic insufficiency and auto degradation