Lipid metabolism — Flashcards

Flashcard 261: 35 y/o man comes with skin lesions on his palms. -Patient has yellowish skin nodules over palmar creases. -It has been increasing in size and number over the past several years. -He has small clusters of yellow papules on his elbows, knees, and buttocks. -Biopsy of skin lesion:accumulation of lipd-laden macrophages. -Lack of ApoE3 & ApoE4 in his circulation lipoproteins. -What is the most likely impaired in this patient?

Answer: Chylomicron remnant uptake by the liver cells. or VLDL remants which means he has high accumulation of the two. due to Familial dysbetalipoproteinemia (type 3). (palmar xanthomas)

Flashcard 262: What is the status of the following in **Carnitine deficiency**? - Acetoacetate - Arachidonic acid - Glutathione - Homocysteine - Lactate - Palmitate (oxidation)

Answer: - **Acetoacetate:** Decreased (impaired ketogenesis) - **Arachidonic acid:** Unaffected - **Glutathione:** Unaffected - **Homocysteine:** Unaffected - **Lactate:** Unaffected - **Palmitate (oxidation):** Decreased (long-chain fatty acids require the carnitine shuttle)

Extra: In **carnitine deficiency**, the transport of long-chain fatty acids (LCFAs) like **palmitate** (C16) into the mitochondria is impaired. **Consequences:** 1. **Impaired β-oxidation**: LCFAs cannot enter the mitochondrial matrix. 2. **Hypoketotic hypoglycemia**: Since β-oxidation is the primary source of acetyl-CoA for ketogenesis and ATP for gluconeogenesis during fasting, levels of ketone bodies (like **acetoacetate**) and glucose fall. 3. **Other metabolites**: Arachidonic acid (membrane phospholipid component), glutathione (antioxidant), homocysteine (methionine cycle), and lactate (glycolysis) are not directly involved in the carnitine shuttle pathway and remain largely unaffected.

Flashcard 263: A patient presents with hypoketotic hypoglycemia triggered by fasting. - What is the most likely enzyme deficiency? - Which substances have deficient synthesis in this patient?

Answer: 1. Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency 2. Ketone bodies (e.g., acetoacetate) MCAD deficiency is the most common fatty acid oxidation disorder. It results in an inability to oxidize fatty acids into acetyl-CoA, leading to impaired ketogenesis and gluconeogenesis during fasting.

Flashcard 264: An 18-month-old boy presents with neurologic regression. - He developed a gradual regression of developmental milestones such as inability to sit with support. - Poor head control, loss of social smile. - Physical exam: enlarged liver and spleen, hypotonia, lack of deep tendon reflexes in all limbs. - Cherry-red spot on fundoscopic exam. The patient most likely has an accumulation of which substrate?

Answer: Sphingomyelin (Due to Niemann-Pick disease, caused by deficiency of sphingomyelinase) Note: Hepatosplenomegaly is present in Niemann-Pick disease but absent in Tay-Sachs disease (which involves GM2 ganglioside accumulation).

Flashcard 265: Accumulation of the following presents with what disease? - Cerebroside sulfate - Galactocerebroside - Globotriaosylceramide - Glucocerebroside - GM2 ganglioside - Sphingomyelin

Answer: - Cerebroside sulfate: Metachromatic leukodystrophy (peripheral neuropathy and ataxia) - Galactocerebroside: Krabbe disease - Globotriaosylceramide: Fabry disease - Glucocerebroside: Gaucher disease - GM2 ganglioside: Tay-Sachs disease - Sphingomyelin: Niemann-Pick disease

Flashcard 266: 3 y/o patient presents with cherry-red spots and loss of motor skills. - Physical exam: No splenomegaly - What is the most likely enzyme deficiency that causes this disease?

Answer: Hexosaminidase A deficiency due to Tay-Sachs disease.

Flashcard 267: Cultured fibroblast taken from an infant suffering from hypotonia & seizures. -It shows an impaired ability to oxidize very long chain fatty acids (VLCFA) & Phytanic acid. -The defect most likely localized to:

Answer: Peroxisomes due to oxidizing very long chain fatty acids & phytanic acid. They usually metabolize in the peroxisomes. Symptoms: neurological symptoms (seizures & hypotonia)

Flashcard 268: What is the mode of inheritance of Niemann Pick disease?_____

Answer: Autosomal recessive

Flashcard 269: Which classes of steroid hormones (2) are decreased in 17-hydroxylase deficiency?_____

Answer: glucocorticoids and androgens

Flashcard 270: What protein is responsible for the rate limiting step in steroidogenesis?_____

Answer: StAR (Steroidogenic acute regulatory protein)