Objective: Six patients with hyperdibasic aminoaciduria are described to highlight LPI clinical heterogeneity and a diagnostic pitfall. Case reports: Patients 1, 2: A soldier, 23y, with short stature, hepatosplenomegaly, osteoporosis, eye lesions, manifested psychotic episodes and seizures after high protein meals. Two SLC7A7 mutations identified in the patient and his 27y sibling ("hyperammonemia of unknown etiology", 1.80 m, centripetal fat, thin extremities, osteoporosis). Patient 3: Albanian 6y with failure to thrive (bone-age 3y), extreme aversion to protein, hepatosplenomegaly, lung lesions (HRCT), osteoporosis. Aminoacid profile indicated LPI. By 12, death from alveolar proteinosis and hemaphagocytosis. Patients 4, 5: Eight-year old with hyperammonemic encephalopathy. LPI diagnosed (two SLC7A9 mutations), also present in his asymptomatic 11y sibling. Patient 6: Male 4y with bronchiolitis (Singulaire regimen) and liver dysfunction. Symptoms with hyperdibasic aminoaciduria indicated LPI. Extensive SLC7A7 analysis negative but SLC7A9, SLC3A1 mutations present.