Dried blood spot analysis: an easy and reliable tool to monitor the biochemical effect of hematopoietic stem cell transplantation in Hurler Syndrome patients

Hurler syndrome (HS), the most severe phenotype in the spectrum of mucopolysaccharidosis type I, is caused by a deficiency of the lysosomal enzyme alpha-L-iduronidase (IDUA). At present, hematopoietic stem cell transplantation (HSCT) is the only treatment able to prevent disease progression in the central nervous system, and therefore considered the treatment of choice in HS patients. Because IDUA enzyme activities after HSCT have been suggested to influence the prognosis of HS patients, monitoring these activities after HSCT remains highly important. The use of dried blood spots (DBS) for enzyme analysis can be a useful alternative to the conventional leukocyte assay. Importantly, this method allows for convenient worldwide shipment, and can therefore be applied to monitor patients from larger areas of the world, or during large-scale international studies. Furthermore, this method requires only a minimal amount of blood. From 13 HS patients receiving HSCT, 36 paired whole blood and DBS samples were analyzed to assess leukocyte and DBS IDUA activities, respectively. To correct for potential interfering factors, simultaneous assay of the alpha-Galactosidase-A (AGA) activity was performed in the DBS samples and an IDUA/AGA ratio was calculated. A strong linear correlation was demonstrated between the DBS IDUA/AGA ratio and the leukocyte IDUA activity (r2 = .875, P < .001). This correlation was applicable to all enzyme activities, including the activities measured early after HSCT as well as heterozygous activities because of mixed chimerism or the use of a carrier donor. These results demonstrate that the DBS method is reliable to monitor the biochemical effect of HSCT in HS patients

Human herpes virus 6 plasma DNA positivity after hematopoietic stem cell transplantation in children: an important risk factor for clinical outcome.

AbstractHuman herpes virus 6 (HHV6) is known to reactivate after hematopoietic stem cell transplantation (HSCT), and has been suggested to be associated with severe clinical manifestations in adults. The clinical significance in children remains unclear. We investigated the incidence of HHV6 reactivation in relation to HSCT-associated morbidity and mortality in children. Between January 2004 and May 2006, 58 pediatric patients, median age 7.6 years (range: 0.1-18.1 years), received their first allogeneic HSCT. After HSCT, HHV6, Epstein Barr Virus (EBV), cytomegalovirus (CMV), and adenovirus (AdV)-plasma loads were weekly measured by quantitative PCR. Clinical features, engraftment, graft-versus-host disease (GVHD), and HSCT-associated mortality and morbidity were monitored. HHV6 reactivations were classified in group I (no reactivation), group II (loads <1000 cp/mL) and group III (loads >1000 cp/mL). CMV, EBV, Herpes Simpex Virus, Varicella Zoster Virus, and AdV-reactivations were treated according to local guidelines. HHV6 was treated only when there was clinical suspicion of disease. Thirty-six HLA-identical and 22 HLA nonidentical grafts were transplanted of which 43 were bone marrow or peripheral blood stem cells grafts and 15 were cord blood (CB) grafts. Median follow-up of the patients was 15.5 (1-35) months. HHV6 reactivation occurred in 39 of 58 (67%) patients with 31 of 39 (80%) occurring within the first 30 days post-HSCT. In 26 of 58 (45%) patients (group III), HHV 6 reactivation was significantly associated with higher nonrelapse mortality (P = .02), using multivariate Cox proportional hazard models and grade 2-4 acute GVHD (P = .03) and chronic GVHD (P = .05) in a multivariate logistic regression analysis. HHV6 reactivation is very common after HSCT in children and is associated with serious transplantation-related morbidity and mortality. Although the exact role of HHV6 reactivation after HSCT has to be elucidated, early detection and initiation of therapy might be of benefit