Birth Defects (Lectures 12 – 14) Flashcards
(12 cards)
What is cyclopia, and what causes it?
Cyclopia is a birth defect where a baby develops one eye due to the failure of the brain and facial midline to separate properly. It is caused by a disruption in the Sonic Hedgehog (Shh) signaling pathway.
How is the Sonic Hedgehog (Shh) pathway linked to cancer?
The Shh pathway, when misregulated, can lead to cancers such as medulloblastoma, a type of brain cancer. This is because Shh controls cell growth and differentiation during development.
What role did cyclopamine play in treating Shh-related cancers?
Cyclopamine, a natural plant compound that blocks Shh signaling, was discovered to counteract the effects of Shh overactivation. It inspired treatments for cancers like medulloblastoma that involve abnormal Shh activity.
Which two signaling centers control limb development, and what molecules do they use?
The Apical Ectodermal Ridge (AER) and Zone of Polarizing Activity (ZPA) control limb development. AER releases FGF8 and ZPA releases Sonic Hedgehog (Shh) to coordinate limb growth and patterning.
What are polydactyly, syndactyly, and phocomelia, and what causes them?
Polydactyly is the presence of extra digits, syndactyly is fused digits, and phocomelia is severe limb shortening. These conditions result from disruptions in signaling pathways during limb development, including FGF8 and Shh.
How did thalidomide cause limb malformations?
Thalidomide interfered with early limb development by disrupting critical signaling processes, particularly those involving AER and ZPA, leading to conditions like phocomelia.
What determines whether an embryo will develop ovaries or testes?
Primary sex determination is based on chromosomes: XX leads to ovaries and XY leads to testes. The Sry gene on the Y chromosome triggers testis development, while Wnt4 supports ovarian development.
What is the difference between primary and secondary sex characteristics?
Primary sex characteristics are the gonads (ovaries or testes), determined by genetic factors like Sry. Secondary sex characteristics are bodily features such as body hair and breast development, influenced by hormones like testosterone and estrogen.
How do AIS and CAH affect sexual development?
AIS (Androgen Insensitivity Syndrome) involves an inability to respond to testosterone, leading to a female phenotype in genetically male individuals. CAH (Congenital Adrenal Hyperplasia) involves excess androgen production in genetically female individuals, causing masculinization.
What is the role of DHT and estrogen in external genitalia development?
External genitalia are bi-potential and can develop into male or female forms. DHT (a derivative of testosterone) promotes male genital development, while estrogen supports female genital development.
