Achondroplasia is an autosomal dominant disorder characterized by disproportionate short stature: the legs and arms of people with achondroplasia are short compared with the head and trunk. The disorder is due to a base substitution in the gene, located on the short arm of chromosome 4, that encodes fibroblast growth factor receptor 3 (FGFR3). Although achondroplasia is clearly inherited as an autosomal dominant trait, more than 80% of the people who have achondroplasia are born to parents with normal stature. This high percentage indicates that most cases are caused by newly arising mutations; these cases (not inherited from an affected parent) are referred to as sporadic. Studies have demonstrated that sporadic cases of achondroplasia are almost always caused by mutations inherited from the father (paternal mutations). In addition, the occurrence of achondroplasia is higher among the children of older fathers; approximately 50% of children with achondroplasia are born to fathers older than 35 years of age. There is no association with maternal age. The mutation rate for achondroplasia (about 4 × 10-5 mutations per gamete) is high compared with those for other genetic disorders. Explain why most spontaneous mutations for achondroplasia are paternal in origin and why the occurrence of achondroplasia is higher among older fathers.
Achondroplasia is an autosomal dominant disorder characterized by
disproportionate short stature: the legs and arms of people with
achondroplasia are short compared with the head and trunk. The
disorder is due to a base substitution in the gene, located on the short
arm of chromosome 4, that encodes fibroblast growth factor receptor 3
(FGFR3).
Although achondroplasia is clearly inherited as an autosomal dominant
trait, more than 80% of the people who have achondroplasia are born to
parents with normal stature. This high percentage indicates that most
cases are caused by newly arising mutations; these cases (not inherited
from an affected parent) are referred to as sporadic. Studies have
demonstrated that sporadic cases of achondroplasia are almost always
caused by mutations inherited from the father (paternal mutations). In
addition, the occurrence of achondroplasia is higher among the children
of older fathers; approximately 50% of children with achondroplasia are
born to fathers older than 35 years of age. There is no association with
maternal age. The mutation rate for achondroplasia (about 4 × 10-5
mutations per gamete) is high compared with those for other genetic
disorders. Explain why most spontaneous mutations for achondroplasia
are paternal in origin and why the occurrence of achondroplasia is
higher among older fathers.
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