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|Prompt=A 3 week old female infant is brought to the emergency room after suffering a seizure. The child was born without abnormalities in an elective cesarean section. The parents report that the child seems lethargic and feeds poorly. The parents noticed the child begin exhibit tremors and jerking movements one hour after feeding. The physician notes that the girl has a strong musty odor and that her skin and hair are particularly light. Which amino acid must the child be supplemented with? | |Prompt=A 3 week old female infant is brought to the emergency room after suffering a seizure. The child was born without abnormalities in an elective cesarean section. The parents report that the child seems lethargic and feeds poorly. The parents noticed the child begin exhibit tremors and jerking movements one hour after feeding. The physician notes that the girl has a strong musty odor and that her skin and hair are particularly light. Which amino acid must the child be supplemented with? | ||
|Explanation=The child in this vignette is suffering from phenylketonuria. Phenylketonuria (PKU) is an autosomal recessive metabolic genetic disorder characterized by a mutation in the gene for the hepatic enzyme phenylalanine hydroxylase, rendering it nonfunctional. This enzyme is necessary to metabolize the amino acid phenylalanine to the amino acid tyrosine. Untreated PKU can lead to mental retardation, seizures, and other serious medical problems. The mainstream treatment for classic PKU patients is a strict phenylalanine-restricted diet supplemented by a medical formula containing amino acids and other nutrients. | |Explanation=The child in this vignette is suffering from phenylketonuria. Phenylketonuria (PKU) is an autosomal recessive metabolic genetic disorder characterized by a mutation in the gene for the hepatic enzyme phenylalanine hydroxylase, rendering it nonfunctional. This enzyme is necessary to metabolize the amino acid phenylalanine to the amino acid tyrosine. Untreated PKU can lead to mental retardation, seizures, and other serious medical problems. The mainstream treatment for classic PKU patients is a strict phenylalanine-restricted diet supplemented by a medical formula containing amino acids and other nutrients. | ||
[[File:Tyrosine_Biosynthesis.png | center]] | [[File:Tyrosine_Biosynthesis.png | center |400px]] | ||
'''Educational Objective:''' Tyrosine becomes essential in patients with phenylketonuria. | '''Educational Objective:''' Tyrosine becomes essential in patients with phenylketonuria. | ||
Revision as of 04:47, 4 September 2013
| Author | PageAuthor::William J Gibson |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry, MainCategory::Genetics |
| Sub Category | SubCategory::General Principles |
| Prompt | [[Prompt::A 3 week old female infant is brought to the emergency room after suffering a seizure. The child was born without abnormalities in an elective cesarean section. The parents report that the child seems lethargic and feeds poorly. The parents noticed the child begin exhibit tremors and jerking movements one hour after feeding. The physician notes that the girl has a strong musty odor and that her skin and hair are particularly light. Which amino acid must the child be supplemented with?]] |
| Answer A | AnswerA::Arginine |
| Answer A Explanation | AnswerAExp::'''Incorrect:''' Arginine is a nonessential amino acid. Arginine serves as a precursor for nitric oxide synthesis. |
| Answer B | AnswerB::Cysteine |
| Answer B Explanation | AnswerBExp::'''Incorrect:''' Cysteine must be supplemented in homocysteinuria. |
| Answer C | AnswerC::Phenylalanine |
| Answer C Explanation | AnswerCExp::'''Incorrect:''' Phenylalanine supplementation would be disastrous for a patient with phenylketonuria. The deleterious effects of phenylketonuria are caused by the accumulation of phenylalanine to toxic concentrations in the body. |
| Answer D | AnswerD::Tryptophan |
| Answer D Explanation | [[AnswerDExp::Incorrect: Tryptophan is required for the synthesis of niacin (vitamin B3). Tryptophan can be deficient in patients with Hartnup disease, malabsorption syndromes, or carcinoid syndrome (caused by excessive conversion of tryptophan into serotonin).]] |
| Answer E | AnswerE::Tyrosine |
| Answer E Explanation | AnswerEExp::'''Correct:''' Tyrosine becomes essential in patients with phenylketonuria. |
| Right Answer | RightAnswer::E |
| Explanation | [[Explanation::The child in this vignette is suffering from phenylketonuria. Phenylketonuria (PKU) is an autosomal recessive metabolic genetic disorder characterized by a mutation in the gene for the hepatic enzyme phenylalanine hydroxylase, rendering it nonfunctional. This enzyme is necessary to metabolize the amino acid phenylalanine to the amino acid tyrosine. Untreated PKU can lead to mental retardation, seizures, and other serious medical problems. The mainstream treatment for classic PKU patients is a strict phenylalanine-restricted diet supplemented by a medical formula containing amino acids and other nutrients.
 Educational Objective: Tyrosine becomes essential in patients with phenylketonuria. References: First Aid 2012 page 112 |
| Approved | Approved::Yes |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |