Genetics: What is the hereditary ppattern for phenylketonuria and what are the s
ID: 98412 • Letter: G
Question
Genetics:
What is the hereditary ppattern for phenylketonuria and what are the signs and sympotoms expected?
What is the basis of Guthrie test?
CASE 7 2-year-old boy with blond hair and blue d hair and blue eyes is brought to his paediatrician. The n the percentile for age and height, and have a mild concern about the noted delay in development. Physical onia and hiperreflexia in both limbs. A Guthrie test is ing back positive. Meanwhile, you pointed to his small than the percentile for a ears to be small tha ap ohaly. His icrocephaly. His parents ar A 2-year-old Perceye aly. His parents are concern about th ianificative for hypertonia and hiperr which you suspect is coming back posi age and height, and hi he boy xam is significative for h prescribed, which parents bed, the need to reduce you ed to reduce the oral intake of phenylalanine.Explanation / Answer
Phenylketonuria is also known as PKU.It is a rare genetic condition that causes an phenylalanine (an amino acid) to build up in the body.Our body uses phenylanine hydroxylase enzyme to convert phenylalanine into tryosine which is needed by the body to create neurotransmitters.
PKU is caused by a defect in the gene that helps to create phenylalanine hydroxylase.In the absence of this the body is unable to break down phenylalanine.This causes a buildup of phenylalanine in the body
PKU is inherited condition caused by a defect in PAH gene.Both parents must pass on a defective version of the PAH gene for their child to inherit the disorder.If only one parent passes the altered gene,the child will not show any symptoms,but will be a carrier of the gene.
SYMPTOMS:
Phenylalanine plays an important role in the production of melanin,the pigment responsible foe skin and hair colour.So the infants often have lighter skin,hair and eyes.
Other symptoms are:
stunted growth
Head size much smaller than normal
Hyperactivity
Jerking movements of the arms and legs
Skin rashes
Seizures
Tremors
Mental disability
PKU is diagnosed by means of Guthrie test.This test was developed by Robert Guthrie.A blood sample is taken from the baby's heel at or as soon as possible after 48 hours.The spot of blood on the filter paper was placed on the surface of agar plate containg a substance that inhibits the growth of bacteria for overnight.Then the diameter of the growth zone is compared to that of a control disc of blood serum to which a known quantity of phe has been added.This permits the estimation of phe in the test disc.
If the screening test is positive,further blood and urine test are required to confirm.
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