Background Mucopolysaccharidosis I (MPS I) comprises a spectrum of clinical manifestations and is divided into three phenotypes reflecting clinical severity: Hurler, HurlerScheie, and Scheie syndromes. There may be important variations in clinical manifestations of this genetic disease in patients residing in different regions of the world.

The STI of HAART in cycles of 4 weeks off/12 weeks on therapy in children with chronically undetectable VL can cause progressively lower viral rebounds followed by a decrease to undetectable levels, with a low risk of severe immunosuppression and without the occurrence of symptoms related to HIV.

Information concerning structured treatment interruptions (STI) of the Highly Active Antiretroviral Therapy (HAART) and their risk for selecting antiretroviral drug resistance in children is scarce. In this study, we searched for antiretroviral drug resistance mutations at the end of five viral rebounds of two children with HIV and a chronically undetectable viral load (VL) who underwent an STI program. The HAART was interrupted for 4 weeks and then restarted and continued for 12 weeks for three cycles. VL, CD4+/CD8+ lymphocytes, and clinical status were evaluated at the end of each STI and at 6 and 12 weeks after HAART was resumed. Treatment of both the patients based on zidovudine+lamivudine+ritonavir remained identical during the study. The reverse transcriptase (RT)- and protease (PR)-coding regions were sequenced at the end of each viral rebound. One patient experienced progressively lower viral rebounds (269000-31300 at the first and third rebounds, respectively), while the other patient did not experience such a reduction, and the VL of both the patients fell to undetectable levels during therapy. In the five viral rebounds examined, no mutations for resistance to protease inhibitors (PIs) were found and the analysis indicated susceptibility to all PIs currently in clinical use. Although the mutation K103R associated with non-nucleoside reverse transcriptase inhibitor resistance was found in two viral rebounds of one patient, the analysis indicated the absence of resistance to RT inhibitors. As no mutation related to antiretroviral drug resistance was found, our results suggest that the STI program evaluated may have a low risk of selecting antiretroviral drug resistance. Nevertheless, further studies evaluating larger cohorts over longer periods are required before definitive conclusions about the safety of STI of HAART in children may be drawn.

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