Lysinuric protein intolerance: Possible genetic heterogeneity?

During the last 4 years we have diagnosed lysinuric protein intolerance (LPI) in two unrelated boys (7 and 3 years old) living in the area around Naples. One of the patients, already reported in the literature as having a possible storage disease, shows peculiar haematological findings and striking joint hyper-extensibility. Both patients have been treated successfully with arginine supplementation and low protein diet. These two cases suggest that LPI might not be so rare in the Neapolitan area and arginine supplementation and low protein diet still represent an acceptable low-cost treatment of the disease. The presence of joint and bone marrow abnormalities in one of the patients, whether casual or due to genetic heterogeneity, should be further investigated.