The following are single gene disorders except
**Core Concept**
Single gene disorders, also known as monogenic disorders, are caused by mutations in a single gene and can result in a wide range of phenotypic expressions. These disorders often have an autosomal dominant, autosomal recessive, or X-linked pattern of inheritance. The identification of single gene disorders is crucial for genetic counseling and targeted therapeutic interventions.
**Why the Correct Answer is Right**
The correct answer is a disorder that does not fit the single gene disorder category. Single gene disorders typically result from mutations in a single gene that disrupts the normal function of a protein. This disruption can lead to a variety of clinical manifestations, depending on the gene involved and the specific mutation. For example, sickle cell anemia is a single gene disorder caused by a mutation in the HBB gene that codes for the beta-globin subunit of hemoglobin.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a single gene disorder caused by a mutation in the CFTR gene that codes for the cystic fibrosis transmembrane conductance regulator protein. Cystic fibrosis is a classic example of a single gene disorder with an autosomal recessive pattern of inheritance.
**Option B:** This option is incorrect because it is a single gene disorder caused by a mutation in the DMD gene that codes for dystrophin. Duchenne muscular dystrophy is a severe form of muscular dystrophy that results from a mutation in the dystrophin gene.
**Option C:** This option is incorrect because it is a single gene disorder caused by a mutation in the BRCA1 gene that codes for a tumor suppressor protein. Breast cancer susceptibility 1 is a single gene disorder that increases the risk of breast and ovarian cancer.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that single gene disorders can result from a wide range of mutations, including point mutations, deletions, duplications, and insertions. The identification of the specific mutation and the gene involved is crucial for targeted therapeutic interventions and genetic counseling.
**Correct Answer:** D