Table of Contents
- Overview
- Prevention
- Images
People with one copy of a recessive disease gene are called carriers. Carriers usually don't show the disease. However, the gene can often be found by sensitive laboratory tests.
In autosomal dominant inheritance, the abnormality or abnormalities usually appear in every generation. Each affected child of an affected parent has a 50% chance of inheriting the disease.
In autosomal recessive inheritance, the parents of an affected individual may not show the disease. On average, the chance of an affected child's brothers or sisters having the disease are 1 in 4. Males and females are equally likely to be affected. For a child to have symptoms of an autosomal recessive disorder, the child must receive the defective gene from both parents.
Because most recessive disorders are rare, a child is at increased risk of a recessive disease if the parents are related. Related individuals are more likely to have inherited the same rare gene from a common ancestor.
In X-linked recessive inheritance, the incidence of the disease is much higher in males than females. Since the abnormal gene is carried on the X chromosome, males do not transmit it to their sons. However, they do transmit it to their daughters.
The presence of one normal X chromosome masks the effects of the X chromosome with the abnormal gene. So, almost all of the daughters of an affected man appear normal, but they are all carriers of the abnormal gene. The sons of these daughters then have a 50% chance of receiving the defective gene.
In X-linked dominant inheritance, the presence of the defective gene appears in females even if there is also a normal X chromosome present. Since males pass the Y chromosome to their sons, affected males will not have affected sons. All of their daughters will be affected, however. Sons or daughters of affected females will have a 50% chance of getting the disease.
EXAMPLES OF SINGLE GENE DISORDERS
Autosomal recessive:
- ADA deficiency (sometimes called the "boy in a bubble" disease)
- Alpha-1-antitrypsin (
AAT ) deficiency -
Cystic fibrosis (CF) - Phenylketonuria (
PKU ) Sickle cell anemia
X-linked recessive:
- Duchenne
muscular dystrophy Hemophilia A
Autosomal dominant:
Familial hypercholesterolemia Huntington's disease
X-linked dominant:
Images
Review Date: 04/26/2010
Reviewed By: Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of
Pediatrics, University of Washington School of Medicine. Also
reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)
