Autosomal Recessive Inheritance Flashcards
Describe the genetic basis and typical clinical presentation of phenylketonuria (PKU).
PKU results from a deficiency of phenylalanine hydroxylase, which is encoded on chromosome 12q and is necessary for conversion of phenylalanine to tyrosine. Typically, PKU homozygotes have fair-colored hair and blue eyes. Children with PKU often develop dry, eczematous skin and experience convulsions, becoming severely mentally retarded early in life. Phenylalanine accumulates in the blood and related metabolites are excreted in the urine. Untreated patients exhibit a “mousy” smell due to phenylacetic acid in the sweat and urine. A phenylalanine-low diet must be introduced well before one month of age and continued for at least 10 years.
What is the name given to the unique body posturing observed in individuals with untreated PKU?
Schneidersitz (or tailor’s posture); it is caused by muscular hypertonicity.
This is the most severe and most common form of spinal muscular atrophy (SMA). Children present within the first six months with severe hypotonia and lack of spontaneous movement. They may have poor swallowing and respiratory function leading to death before the age of three years. Name this disease and describe the genetic basis.
Werdnig-Hoffmann disease (or type 1 SMA), an autosomal recessive disease caused by a genetic defect in the SMN1 gene on chromosome 5q. Disability in this disease is due to degeneration of the anterior horn cells of the spinal cord, which leads to progressive muscle weakness and ultimately death.
