What percentage of male offspring is affected by X-linked ichthyosis associated with placental steroid sulfatase deficiency?

What percentage of male offspring is affected by X-linked ichthyosis associated with placental steroid sulfatase deficiency?

• A. 50%
• B. 75%
• C. 90%
• D. 100%

Answer: (C)

X-linked ichthyosis is a genetic condition caused by a deficiency in the enzyme steroid sulfatase, which is located on the X chromosome. This condition predominantly affects males because they have only one X chromosome; consequently, a single altered copy of the gene will manifest the disease in male offspring. For female offspring, who possess two X chromosomes, one normal allele can often mask the effects of the disorder. Therefore, females are typically carriers without showing the full phenotype unless both X chromosomes carry the mutation, which is much less common. When an affected male (who has the genotype X*Y, where X* represents the mutated X chromosome) has children, all of his daughters will inherit his X chromosome, thus being carriers (X*/X). However, his sons will inherit his Y chromosome, resulting in a normal-expressing Y male (Y) and not inheriting the mutated X chromosome. In situations where an affected male reproduces, looking solely at the male offspring, since they would receive a Y from their father, the likelihood of a male offspring being affected is directly related to the genetic inheritance highlighted by the X-linked pattern. Therefore, 100% ofoffspring male from an affected male will not carry the disorder because they

X-linked ichthyosis is a genetic condition caused by a deficiency in the enzyme steroid sulfatase, which is located on the X chromosome. This condition predominantly affects males because they have only one X chromosome; consequently, a single altered copy of the gene will manifest the disease in male offspring.

For female offspring, who possess two X chromosomes, one normal allele can often mask the effects of the disorder. Therefore, females are typically carriers without showing the full phenotype unless both X chromosomes carry the mutation, which is much less common.

When an affected male (who has the genotype XY, where X represents the mutated X chromosome) has children, all of his daughters will inherit his X chromosome, thus being carriers (X*/X). However, his sons will inherit his Y chromosome, resulting in a normal-expressing Y male (Y) and not inheriting the mutated X chromosome.

In situations where an affected male reproduces, looking solely at the male offspring, since they would receive a Y from their father, the likelihood of a male offspring being affected is directly related to the genetic inheritance highlighted by the X-linked pattern. Therefore, 100% ofoffspring male from an affected male will not carry the disorder because they