An Infant Who Is 4 Days Postpartum Has Been Diagnosed

An infant who is 4 days postpartum has been diagnosed with a single-gene disorder. The parents of the child have a number of questions about the etiology of the health problem, which the physician is attempting to address in detail. Which of the following teaching points most accurately captures an aspect of single-gene congenital disorders?

A) Affected genes are present on autosomal chromosomes rather than sex chromosomes.
B) The majority of single-gene disorders manifest near the time of puberty.
C) A particular defect can be caused by mutations at several different loci.
D) Single-gene disorders are associated with existing rather than new mutations.