Question

1. Compare and contrast the diseases epidermolysis bullosa simplex (EBS) and sickle cell anemia. Include molecular level details for one similarity and three differences.

Answer 1

Answer:

Similarities:

1):

• Both occur due to arising mutations in the gene.
• In Osteogenesis imperfecta (OI) mutations occur in COL1A1 or COL1A2 genes; Epidermolysis bullosa simplex (EBS) mutations occur in keratin-5 gene (KRT5) on chromosome 12 or on the keratin-14 gene (KRT14) on chromosome 17.

2):

• Both Osteogenesis imperfecta (OI) and Epidermolysis bullosa simplex (EBS) are inherited in Autosomal Dominant maner.

3):

• In both OI and EBS, Dental problems, such as tooth decay or brittle teeth symptoms are seen.

Differences:

• In Osteogenesis Imperfecta (OI), the people are born with defective connective tissue due to defective Type-I collagen.
• In this case, in the collagen triple helix structure, amino acid glycine is replaced with bulkier amino acids having larger amino acid side-chains that create steric hindrance in collagen complex leading to creating bulges in the collagen triple helix structure; and as a result the interaction between the collagen structure and also the nanomechanics of the collagen structure gets disturbed.
• So, the body tries to respond to this situation by hydrolyzing the improper collagen structure and if the body fails to hydrolyze the improper collagen, it will hinder the bone formation by not letting collagen fibrils and hydroxyapatite crystals to interact (this step is very vital in bone formation). This will in turn lead to fragile bones.
• EBS is caused by defective KRT14 and KRT5 gene.
• The KRT14 gene encodes a protein called keratin 14 which partners with a similar protein known as keratin 5 encoded by KRT5 gene.
• Keratins form the structural framework of the cells that make up the skin, hair, nail etc.
• Keratin 14 and keratin 5 interact to form keratin intermediate filaments which help in attaching the keratinocytes of the outer layer of skin i.e. epidermis to the underlying layers of skin (endodermis), thus providing strength to the skin so that the skin becomes resilient and do not easily get damaged by friction and physical stresses.
• If any of these genes get mutated, that can lead to fragile skin, development of blisters in the skin and lead to EBS.

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