Diabetes mellitus is caused by insulin deficiency or resista

[Hijeck]

Diabetes mellitus is caused by insulin deficiency or resistance with decreased import of glucose into extrahepatic tissues. Juvenile-onset (type I) cases often follow a viral infection with inflammation of the pancreatic β cells. Adult-onset (type II) cases are strongly associated with obesity. Each type exhibits genetic predisposition with a 40-50% concordance rate in monozygous twins and clustering in families. Diabetes mellitus is best described as which of the following types of disorders?

a. Congenital disorder
b. Multifactorial disorder
c. Mendelian disorder
d. Sporadic disorder
e. Sex-limited disorder

[Hijeck]

Answer: b

DM is associated with various risk factors, from autoimmune mechanisms to obesity. The multifactorial causation and hereditary tendency reflects multiple genes and environmental factors, so it is multifactorial determination.

[Hijeck]

Tay-Sachs disease is an autosomal recessive disorder for which the carrier frequency in individuals of Ashkenazi Jewish descent is about 1 in 30. On the basis of this carrier frequency, which of the following is the best estimate of the probability that a child born to two parents, both of whom are of Ashkenazi Jewish descent, will be affected by Tay-Sachs disease?
A ) 1 in 15
B ) 1 in 60
C ) 1 in 450
D ) 1 in 900
E ) 1 in 1800
F ) 1 in 3600

[Hijeck]

F

To determine the joint probability of two or more independent events, the product of their separate probabilities must be determined. If the parents were both Ashkenazi Jews, they would have a 1/30 chance of carrying an abnormal gene for Tay-Sachs disease; for each pregnancy, they would have a 1/2 chance of passing that gene along should they carry it. The probability that all of these four independent events would occur is 1/30 × 1/2 × 1/30 × 1/2 = 1/3600. The joint probability for a mother who is an Ashkenazi Jew and a father who is not is 1/30 × 1/2 × 1/300 × 1/2 = 1/36,000.