Inborn errors of amino acid metabolism

Question 0

Alkaptonuria

Answer 0

• deficient in homogentisate1,2- dioxegenase which is involved in the tyrosine degradation pathway
• asymptomatic in childhood
• dark gray or black pigmentation of sclera or ear cartilage
• darkened sweat or cerumen
• urine turns dark when left out
• arthritis develops and progresses to ankylosis of the spine
• high incidence of heart disease and MI

Question 1

Homocysteinuria

Answer 1

• deficient in cystathionine synthase leading to increased methionine in the blood
• unpleasant odor
• more lightly pigmented skin, hair, and eyes than family members
• dislocation of the lens downward, myopia, cataracts, and retinal detachment
• tall stature, thin body habits, pectins excavatum, arachnodactyly, narrow palatal contour, scoliosis
• B6 nonresponsive IQ of 57, B6 responsive IQ of 79
• included on all newborn screens

Question 2

Nonketotic hyperglycinemia

Answer 2

• deficient activity of proteins in the glycine cleavage system
• presents in the first few days after birth
• Develop anorexia and lethargy, progresses to coma
• survivors develop severe spastic CP

Question 3

Oculocutaneous tyrosinemia (type II)

Answer 3

• hepatic deficiency of tyrosine aminotransferase in the cytosol
• corneal erosions, ulcers, and plaques leading to corneal clouding and vision impairment
• present with tearing, photophobia, eye redness and pain
• painful keratoses on pressure bearing regions, such as palms and soles
• treatment involves instituting a diet low in tyrosine and phenylalanine

Question 4

Phenylketonuria

Answer 4

• near complete deficiency of phenylalanine hydroxylase which converts phenylalanine to tyrosine
• intellectual disability
• vomiting, irritability, rash, musty odor
• many are light eyed, fair skinned, and light haired compared to family
• treatment is a diet low in phenylalanine and tyrosine supplementation
• included on all heel sticks