Lysinuric protein intolerance (LPI) may present in early childhood. It is due to an inherited defect in cellular transport of cationic amino acids.


Synonym: familial protein intolerance, hyperdibasic aminoaciduria type 2


Inheritance: autosomal recessive


Clinical findings:

(1) asymptomatic during early infancy, especially if breast fed

(2) poor appetite with failure to thrive after weaning

(3) vomiting and diarrhea

(4) poor growth

(5) irritability

(6) hepatosplenomegaly

(7) muscle hypotonia

(8) sparse hair

(9) osteoporosis with increased risk for fracture

(10) normal mental development to moderate retardation

(11) malabsorption with villous atrophy in small bowel

(12) poor response to a protein rich diet and aversion to dietary protein

(13) positive clinical response to a diet with oral citrulline

(14) affected women may have high risk pregnancies

(15) may develop acute or chronic pulmonary disease with interstitial fibrosis and/or alveolar proteinosis

(16) may develop nephritis with renal insufficiency


Laboratory findings:

(1) increased urine excretion of lysine and other cationic amino acids (arginine, ornithine)

(2) increased urine excretion of orotic acid after a protein meal

(3) anemia and thrombocytopenia

(4) hypoalbuminemia associated with protein malnutrition

(5) hyperammonemia after a protein meal


Differential diagnosis:

(1) other aminoacidurias

(2) celiac disease


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