Attention and corpus callosum volumes in individuals with mucopolysaccharidosis type I.

OBJECTIVE: Previous research suggests attention and white matter (WM) abnormalities in individuals with mucopolysaccharidosis type I (MPS I); this cross-sectional comparison is one of the first to examine the relationship of WM structural abnormalities as measured by corpus callosum (CC) volumes with attention scores to evaluate this relationship in a larger sample of patients with MPS I. METHODS: Volumetric MRI data and performance on a computerized measure of sustained attention were compared for 18 participants with the severe form of MPS I (MPS IH), 18 participants with the attenuated form of MPS I (MPS IATT), and 60 typically developing age-matched controls. RESULTS: The MPS I groups showed below-average mean attention scores (p < 0.001) and smaller CC volumes (p < 0.001) than controls. No significant associations were found between attention performance and CC volume for controls. Attention was associated with posterior CC volumes in the participants with MPS IH (p = 0.053) and total (p = 0.007) and anterior (p < 0.001) CC volumes in participants with MPS IATT. CONCLUSIONS: We found that attention and CC volumes were reduced in participants with MPS I compared to typically developing controls. Smaller CC volumes in participants with MPS I were associated with decreased attention; such an association was not seen in controls. While hematopoietic cell transplantation used to treat MPS IH may compound these effects, attention difficulties were also seen in the MPS IATT group, suggesting that disease effects contribute substantially to the clinical attentional difficulties seen in this population.

Intrathecal enzyme replacement therapy reverses cognitive decline in mucopolysaccharidosis type I.

Mucopolysaccharidosis type I (MPS I) is an inherited lysosomal storage disease that seriously affects the brain. Severity of neurocognitive symptoms in attenuated MPS subtype (MPS IA) broadly varies partially, due to restricted permeability of blood-brain barrier (BBB) which limits treatment effects of intravenously applied α-L-iduronidase (rhIDU) enzyme. Intrathecal (IT) rhIDU application as a possible solution to circumvent BBB improved brain outcomes in canine models; therefore, our study quantifies effects of IT rhIDU on brain structure and function in an MPS IA patient with previous progressive cognitive decline. Neuropsychological testing and MRIs were performed twice prior (baseline, at 1 year) and twice after initiating IT rhIDU (at 2nd and 3rd years). The difference between pre- and post-treatment means was evaluated as a percentage of the change. Neurocognitive performance improved particularly in memory tests and resulted in improved school performance after IT rhIDU treatment. White matter (WM) integrity improved together with an increase of WM and corpus callosum volumes. Hippocampal and gray matter volume decreased which may either parallel reduction of glycosaminoglycan storage or reflect typical longitudinal brain changes in early adulthood. In conclusion, our outcomes suggest neurological benefits of IT rhIDU compared to the intravenous administration on brain structure and function in a single MPS IA patient.© 2017 Wiley Periodicals, Inc.

Cognitive outcomes and age of detection of severe mucopolysaccharidosis type 1.

The US Secretary of Health and Human Services recommended in February 2016 that mucopolysaccharidosis type 1 (MPS I) be added to the recommended uniform screening panel for state newborn screening programs. One of the key factors in this decision was the evidence suggesting that earlier treatment with hematopoietic cell transplantation (HCT) for the most severe form, Hurler syndrome (MPS IH), would lead to improved cognitive outcomes. Consistent evidence from peer-reviewed studies suggests that transplantation in the first year of life is associated with improved developmental quotient or intelligence quotient and continued cognitive growth, with earlier age of treatment associated with improved outcomes. However, available evidence suggests that cognitive functioning and attention can still lag behind unaffected age-matched children, leading to the need for special education services. Verbal and nonverbal cognitive abilities outcomes may be affected differently by HCT. With the recent addition of MPS I to the recommended uniform screening panel, future work is needed to evaluate the impact of earlier, presymptomatic detection and treatment initiation and other supportive therapies on cognitive outcomes.Genet Med advance online publication 26 January 2017.

Neurodevelopmental Outcome after Hematopoietic Cell Transplantation in Inborn Errors of Metabolism: Current Considerations and Future Perspectives.

Inborn errors of metabolism (IEM) comprise an assorted group of inherited diseases, some of which are due to disordered lysosomal or peroxisomal function and some of which might be improved following hematopoietic cell transplantation (HCT). In these disorders the onset in infancy or early childhood is typically accompanied by rapid deterioration, resulting in early death in the more severe phenotypes. Timely diagnosis and immediate referral to an IEM specialist are essential steps in optimal management. Treatment recommendations are based on the diagnosis, its phenotype, rate of progression, prior extent of disease, family values, and expectations, and the risks and benefits associated with available therapies, including HCT. International collaborative efforts are of utmost importance in determining outcomes of therapy for these rare diseases, and have improved those outcomes significantly over the last decades. In this review, we will focus on the neurodevelopmental outcomes after HCT in IEM, providing an international perspective on progress, limitations, and future directions.

Mental retardation in mucopolysaccharidoses correlates with high molecular weight urinary heparan sulphate derived glucosamine.

Mucopolysaccharidoses (MPS) are characterized by mental retardation constantly present in the severe forms of Hurler (MPS I), Hunter (MPS II) and Sanfilippo (MPS III) diseases. On the contrary, mental retardation is absent in Morquio (MPS IV) and Maroteaux-Lamy (MPS VI) diseases and absent or only minimal in the attenuated forms of MPS I, II and III. Considering that MPS patients affected by mental disease accumulate heparan sulfate (HS) due to specific enzymatic defects, we hypothesized a possible correlation between urinary HS-derived glucosamine (GlcN) accumulated in tissues and excreted in biological fluids and mental retardation. 83 healthy subjects were found to excrete HS in the form of fragments due to the activity of catabolic enzymes that are absent or impaired in MPS patients. On the contrary, urinary HS in 44 patients was observed to be composed of high molecular weight polymer and fragments of various lengths depending on MPS types. On this basis we correlated mental retardation with GlcN belonging to high and low molecular weight HS. We demonstrate a positive relationship between the accumulation of high molecular weight HS and mental retardation in MPS severe compared to attenuated forms. This is also supported by the consideration that accumulation of other GAGs different from HS, as in MPS IV and MPS VI, and low molecular weight HS fragments do not impact on central nervous system disease.

Long-term outcome of Hurler syndrome patients after hematopoietic cell transplantation: an international multicenter study.

Mucopolysaccharidosis type I-Hurler syndrome (MPS-IH) is a lysosomal storage disease characterized by multisystem morbidity and death in early childhood. Although hematopoietic cell transplantation (HCT) has been performed in these patients for more than 30 years, large studies on the long-term outcome of patients with MPS-IH after HCT are lacking. The goal of this international study was to identify predictors of the long-term outcome of patients with MPS-IH after successful HCT. Two hundred seventeen patients with MPS-IH successfully engrafted with a median follow-up age of 9.2 years were included in this retrospective analysis. Primary endpoints were neurodevelopmental outcomes and growth. Secondary endpoints included neurologic, orthopedic, cardiac, respiratory, ophthalmologic, audiologic, and endocrinologic outcomes. Considerable residual disease burden was observed in the majority of the transplanted patients with MPS-IH, with high variability between patients. Preservation of cognitive function at HCT and a younger age at transplantation were major predictors for superior cognitive development posttransplant. A normal α-l-iduronidase enzyme level obtained post-HCT was another highly significant predictor for superior long-term outcome in most organ systems. The long-term prognosis of patients with MPS-IH receiving HCT can be improved by reducing the age at HCT through earlier diagnosis, as well as using exclusively noncarrier donors and achieving complete donor chimerism.

Early treatment is associated with improved cognition in Hurler syndrome.

OBJECTIVE: Hurler syndrome is the most clinically severe form of an autosomal recessive lysosomal disorder characterized by the deficiency of α-L-iduronidase. The resulting accumulation of glycosaminoglycans causes progressive multisystem deterioration, resulting in death in childhood. Umbilical cord blood transplantation from unrelated donors has been previously shown to improve neurological outcomes of children <2 years of age and prolong life. The purpose of this article is to determine whether age at transplantation can predict cognitive outcomes. METHODS: Between June 1997 and February 2013, 31 patients with Hurler syndrome underwent umbilical cord blood transplantation and were evaluated at baseline and every 6 to 12 months thereafter. All 31 patients underwent complete neurodevelopmental evaluation (median follow-up = 7.3 years, range = 2-21.7) and a median of 7.0 evaluations (range = 3-18). RESULTS: Younger age at transplantation was associated with improved cognitive function (p = 0.001), receptive and expressive language (p = 0.004 and p = 0.01), and adaptive behavior (p = 0.03). INTERPRETATION: Early age at transplantation is a strong predictor of cognitive, language, and adaptive behavior outcomes. Children younger than 9 months at the time of transplant showed normal cognitive development. Our results demonstrate that early diagnosis is necessary for optimal outcomes and support the need for newborn screening, because most patients are not identified at this young age.

High-dose enzyme replacement therapy in murine Hurler syndrome.

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive disease that is systemic, including progressive neurodegeneration, mental retardation and death before the age of 10 years. MPS I results from deficiency of α-L-iduronidase (IDUA) in lysosomes and subsequent accumulation of glycosaminoglycans (GAG). Clinical enzyme replacement therapy (ERT) with intravenous laronidase reverses some aspects of MPS I disease (e.g., hepatomegaly, splenomegaly, glycosaminoglycanuria) and ameliorates others (e.g., pulmonary function, cardiac disease, arthropathy, exercise tolerance). However, neurologic benefits are thought to be negligible because the blood-brain barrier (BBB) blocks enzyme from reaching the central nervous system (CNS). We considered the possibility that a very high dose of intravenous laronidase might be able to traverse the BBB in small quantities, and provide some metabolic correction in the brain. To address this question, high-dose laronidase was administered (11.6 mg/kg, once per week, 4 weeks) to adult MPS I mice. IDUA enzyme activity in the cortex of treated mice increased to 97% of that in wild type mice (p<0.01). GAG levels in cortex were reduced by 63% of that from untreated MPS I mice (p<0.05). Further, immunohistochemical analysis showed that treatment reduced secondary GM3-ganglioside accumulation in treated MPS I mice. Water T-maze tests showed that the learning abnormality in MPS I mice was reduced (p<0.0001). In summary, repeated, high-dose ERT facilitated laronidase transit across the BBB, reduced GAG accumulation within the CNS, and rescued cognitive impairment.

Neurocognitive and neuropsychiatric phenotypes associated with the mutation L238Q of the α-L-iduronidase gene in Hurler-Scheie syndrome.

UNLABELLED: The lysosomal enzyme α-L-iduronidase hydrolyzes terminal iduronic acid from heparan sulfate and dermatan sulfate, and is an essential step in GAG degradation. Mutations of its gene, IDUA, yield a spectrum of mucopolysaccharidosis (MPS) type I clinical disorders. The IDUA mutation, c.712T>A (p.L238Q) was previously noted as a mild mutation. In a longitudinal study of MPS brain structure and function (Lysosomal Disease Network), we found this mutation in 6 of 14 Hurler-Scheie syndrome patients in the age range of 15 to 25 years. We hypothesized that L238Q, when paired with a nonsense mutation, is significantly more severe than other missense-nonsense combinations. METHODS: Of 6 patients with a L238Q mutation, the L238Q allele was paired with a nonsense mutation in 4 patients, paired with a deletion in 1, and with a splice site mutation in another. This group was compared to 6 Hurler-Scheie patients closely matched in age and mutation type. IQ and other neuropsychological tests were administered as part of the protocol. Medical history was compiled into a Physical Symptom Score (PSS). Assessment of IQ, attention, memory, spatial ability, adaptive function and psychological status were measured. RESULTS: No group differences were found in mean age at evaluation (17.8 and 19.0 years), duration of ERT, or PSS. By history, all were reported to be average in IQ (4/6 with documentation) in early childhood. All (100%) of the L238Q group had a psychiatric history and sleep problems compared to none (0%) of the comparison group. Significant differences were found in depression and withdrawal on parent report measures. IQ was lower in the L238Q group (mean IQ 74) than the comparison group (mean IQ 95; p<0.016). Attention, memory, and visual-spatial ability scores were also significantly lower. Three occurrences of shunted hydrocephalus, and 4 of cervical cord compression were found in the L238Q group; the comparison group had one occurrence of unshunted hydrocephalus and two of cord compression. DISCUSSION: The missense mutation L238Q, when paired with a nonsense mutation, is associated with significant, late-onset brain disease: psychiatric disorder, cognitive deficit, and general decline starting at a later age than in Hurler syndrome with a mutation-related rate of GAG accumulation and its pathologic sequelae. This particular genotype-phenotype may provide insight into the genesis of psychiatric illnesses more broadly. Consideration of methods for early, brain-targeted treatment in these patients might be considered.

An exploratory study of brain function and structure in mucopolysaccharidosis type I: long term observations following hematopoietic cell transplantation (HCT).

AIM: Although hematopoietic cell transplantation (HCT) arrests the cognitive decline in mucopolysaccharidosis type IH (Hurler syndrome, MPS IH), these children continue to have neuropsychological deficits as they age. Both compromised attention and effects on white matter have been observed in cancer patients who have had chemotherapy. Therefore, we explored the effects of disease and treatment on brain function in children with MPS I who have had HCT with those with attenuated MPS I treated with enzyme replacement therapy (ERT). SUBJECTS: 7 MPS IH participants at least 5 years post-HCT were compared with 7 attenuated participants who were treated with ERT. MEASURES: IQ, attention, spatial ability, and memory were assessed. Medical history and an unsedated MRI scan using diffusion tensor imaging (DTI) were acquired. RESULTS: Despite clinically equivalent IQ and memory, children with MPS IH had poorer attention span than those with attenuated MPS I as well as decreased fractional anisotropy (FA) of the corpus callosum. A relationship between attention scores and FA was found in the MPS IH group but not the attenuated group. FA was also related to the frequency of medical events. INTERPRETATION: In children with MPS IH, both the treatment and the disease affect attention functions associated with poor white matter integrity.

Experiences of parents and patients with the timing of Mucopolysaccharidosis type I (MPS I) diagnoses and its relevance to the ethical debate on newborn screening.

INTRODUCTION: Newborn screening (NBS) techniques have been developed for several lysosomal storage disorders (LSDs), including Mucopolysaccharidosis type I (MPS I). MPS I is an LSD with a wide phenotypic spectrum that ranges from the severe Hurler phenotype to the attenuated Scheie phenotype. To improve the ethical discussion about NBS for MPS I, we performed an interview study to explore the experiences of MPS I patients and their parents with the timings of their diagnoses. METHODS: We used a qualitative research approach consisting of 17 interviews with the parents of patients with all MPS I phenotypes and with patients with attenuated forms of MPS I. The interviews were audio-recorded, transcribed and subsequently analyzed to identify the main themes identified by the participants. RESULTS: Five important themes, focusing on the experienced disadvantages of delayed diagnosis and the advantages and disadvantages of a hypothetical earlier diagnosis, were identified in our group of participants: 1) delayed diagnosis causing parental frustration, 2) delayed diagnosis causing patient frustration, 3) early diagnosis enabling reproductive decision-making, 4) early diagnosis enabling focusing on the diagnosis, and 5) early diagnosis enabling timely initiation of treatment. There was a remarkable similarity in the experiences with timing of diagnosis between parents of patients with the severe and the attenuated forms. CONCLUSION: This was the first study to explore the personal experiences of MPS I patients and their parents with diagnostic timing. Our study identified five important themes that are highly relevant to the ethical discussion on expanding NBS programs for MPS I.

Laronidase for cardiopulmonary disease in Hurler syndrome 12 years after bone marrow transplantation.

A patient with severe mucopolysaccharidosis type I (Hurler syndrome) underwent bone marrow transplantation twice (at the ages of 2 and 2.5 years), both times with his HLA-identical heterozygous brother as the donor. Between the ages of 10 and 14 years, despite 92% donor engraftment and 50% normal α-L-iduronidase activity, he developed progressive respiratory failure with severe pulmonary arterial hypertension, upper airway obstruction, and interstitial lung disease. Noninvasive ventilation and weekly laronidase therapy were initiated. Within 24 months, his mean pulmonary artery pressure was within the upper limit of normal and interstitial lung disease and airway obstruction improved markedly. He went from using a wheelchair to having full ambulation, he no longer required daytime ventilation, and his quality-of-life scores (Child Health Assessment Questionnaire) significantly improved.

Cord blood and bone marrow transplantation in inherited metabolic diseases: scientific basis, current status and future directions.

Progressive degeneration of the central nervous system leading to the loss of neuromotor, neurophysiological and cognitive abilities is the fundamental clinical problem in patients with many inherited metabolic diseases (IMD). Worldwide experience shows that morbidity, quality of life, and survival in these patients can be improved by allogeneic haematopoietic stem cell transplantation (HSCT), particularly when performed early in the course of the disease. At present, while available for some conditions, exogenous enzyme replacement therapy is unable to correct cognitive and central nervous system disease because of its inability to cross the blood-brain barrier. In contrast, HSCT allows donor-derived, enzyme-producing cells to migrate to the brain and other organs providing a permanent enzyme replacement therapy. HSCT may also mediate non-hematopoietic cell regeneration or repair. Traditionally, bone marrow has been the graft source for IMD patients. However, in the last 5 years many studies utilizing unrelated donor umbilical cord blood (UCB) as a graft source have demonstrated that UCB provides rapid and increased access to transplantation with favourable outcomes. This review describes preclinical studies and past and present clinical treatment approaches and discusses current controversies and future directions of this promising field.

Psychosocial outcomes of bone marrow transplant for individuals affected by Mucopolysaccharidosis I Hurler Disease: patient social competency.

AIM: To explore the frequency with which children and young people participate in social activities with peers, when they are affected by Mucopolysaccharidosis I Hurler Disease (MPS IH) post bone marrow transplant (BMT). This was investigated in relation to patient age, and in comparison with a normative sample. Patient withdrawal, adaptive and social skills are also described in terms of patient age and in comparison with a normative sample. METHOD: Forty-four individuals affected by MPS IH post BMT participated in this investigation. Their ages ranged from 16 months to 25 years. Semi-structured interviews with patients' mothers were utilized, which included the Behaviour Assessment System for Children and a socialization questionnaire. Normative data for the socialization questionnaire were collected from 46 mothers of children not affected by chronic illness or disability. RESULTS: A one-way ANOVA revealed that children not affected by disability or chronic illness (mean = 20.63) participated overall in social activities more frequently than children aged under 12 years (mean = 14.87) and over 12 years (mean = 13.25) who were affected by MPS IH post BMT (F = 21.01, P < 0.001). Young people aged 12 years and over affected by this condition were found to participate in social activities the least. A pattern also emerged, which indicated greater withdrawal and less well-developed adaptive and social skills for MPS IH patients aged 2.5-5 years and 12 years and over, but scores were within the normal range for those aged 6-11 years. CONCLUSION: These data illustrate a lack of social competency and a tendency towards inhibition and withdrawal in this patient group, particularly among the very young children and the adolescents and young adults. Further research is needed to explore these issues longitudinally and to examine the role played by the family, and indeed disability, in the quality and quantity of social interaction experienced by these individuals.

Gross motor abilities in children with Hurler syndrome.

Hurler syndrome is the most severe form of mucopolysaccharidosis type I. There is a paucity of literature reporting the gross motor abilities of children with untreated Hurler syndrome. The purpose of this case series is to describe the gross motor abilities of one male and three female children (mean age 11.4mo [SD 3.1]; range 9.5-16mo) diagnosed with Hurler syndrome. The children were assessed using the Peabody Developmental Motor Scales, 2nd edition. Gross motor delays were present in all four children at the time of assessment, and were most evident in locomotor abilities for three of the children. All four children had range of motion limitations at multiple joints. This case series provides evidence for early gross motor delays in this population, as well as evidence for specific gross motor abilities of children with untreated Hurler syndrome. It is recommended that children diagnosed with Hurler syndrome be referred to physical therapy services upon diagnosis and that physical therapists be part of the interdisciplinary team involved in the care of children with Hurler syndrome.

Long-term outcomes of adaptive functions for children with mucopolysaccharidosis I (Hurler syndrome) treated with hematopoietic stem cell transplantation.

Advances in medical treatment have prolonged the lives of children with Hurler syndrome or mucopolysaccharidosis I requiring increased attention to the assessment of their long-term outcomes and functional abilities. Adaptive functions are critical for understanding functional outcomes after treatment and developing focused interventions. We investigated the development of various adaptive functions in children who have had hematopoietic stem cell transplant (HSCT) for Hurler syndrome and risk factors that are associated with the development of these functions. We examined the development of 41 children who had 3 or more Vineland Adaptive Behavior Scales records assessed before and after transplant. Communication, daily living skills, socialization, and motor functions were measured. While standard scores decline over time, development of skills continue with a slower than average rate compared with peers. A cross-sectional nontransplanted comparison group showed more deficits after age 2 years than the transplanted group. In contrast to cognitive ability, age at transplant was not significantly associated with ultimate adaptive level. Baseline cognitive level before HSCT and growth of cognition after HSCT were associated with adaptive functions especially for communication and daily living skills. Socialization was predicted by cumulative medical risk factors, likely due to restricted social exposure in children with complicated transplant courses. Overall, measurement of adaptive behaviors demonstrated that HSCT allows long-term slow improvement of functional outcomes for children with Hurler syndrome. Children with Hurler syndrome with good cognitive levels before HSCT and continued growth of cognition after HSCT show good adaptive functions. Although cognitive and orthopedic problems as well as medical complications limit adaptive ability, identifying these problems early allow beneficial targeted interventions.

Gross and fine motor skills of children with Hurler syndrome (MPS-IH) post umbilical cord blood transplantation: a case series report.

PURPOSE: Recent advancements in medical treatment of Hurler syndrome have resulted in longer life expectancies and a greater need for therapeutic services. The purpose of this case series is to provide recommendations for assessing children with Hurler syndrome after umbilical cord blood transplant (UCBT). CLINICAL DESCRIPTIONS: Two children with Hurler syndrome were seen for longitudinal assessments following an UCBT for Hurler syndrome. METHODS: The raw scores and percentage of fine and gross motor items each child completed on the Motor Scale of the Bayley Scales of Infant Development II (BSID-II) were reviewed. RESULTS: Both children gained new motor skills with each successive motor assessment. Both children were able to complete a higher percentage of fine motor skills than gross motor skills in the most advanced item set assessed. DISCUSSION: The children presented in these two case reports both had better fine motor skills than gross motor skills, which inflated their standard scores on the BSID-II. Clinicians assessing children with Hurler syndrome should use standardized assessments that allow for differentiation of fine and gross motor skills to prevent this situation.

Cord-blood transplants from unrelated donors in patients with Hurler's syndrome.

BACKGROUND: Hurler's syndrome (the most severe form of mucopolysaccharidosis type I) causes progressive deterioration of the central nervous system and death in childhood. Allogeneic bone marrow transplantation before the age of two years halts disease progression and prolongs life, but many children lack a bone marrow donor. We investigated the feasibility of using cord-blood transplants from unrelated donors and a myeloablative preparative regimen that did not involve total-body irradiation in young children with Hurler's syndrome. METHODS: Between December 1995 and October 2002, 20 consecutive children with Hurler's syndrome received busulfan, cyclophosphamide, and antithymocyte globulin before receiving cord-blood transplants from unrelated donors. The children were subsequently evaluated for engraftment, adverse effects, and effects on disease symptoms. RESULTS: Cord-blood donors had normal alpha-L-iduronidase activity (mean number of cells, 10.53x10(7) per kilogram of body weight) and were discordant for up to three of six HLA markers. Neutrophil engraftment occurred a median of 24 days after transplantation. Five patients had grade II or grade III acute graft-versus-host disease; none had extensive chronic graft-versus-host disease. Seventeen of the 20 children were alive a median of 905 days after transplantation, with complete donor chimerism and normal peripheral-blood alpha-L-iduronidase activity (event-free survival rate, 85 percent). Transplantation improved neurocognitive performance and decreased somatic features of Hurler's syndrome. CONCLUSIONS: Cord blood from unrelated donors appears to be an excellent source of stem cells for transplantation in patients with Hurler's syndrome. Sustained engraftment can be achieved without total-body irradiation. Cord-blood transplantation favorably altered the natural history of Hurler's syndrome and thus may be important to consider in young children with this form of the disease.

Outcome of 27 patients with Hurler's syndrome transplanted from either related or unrelated haematopoietic stem cell sources.

Over the last 15 years, we have performed a total of 30 haematopoietic stem cell transplants on 27 children suffering from Hurler's syndrome. These children were of median age 11 months at the time of diagnosis and 25 months at the time of transplantation. The phenotype was severe in 21 cases (78%). The donor was familial in 13 cases: nine genotypically identical, one phenotypically identical father and three HLA-mismatched donors. Unrelated donors were selected in 17 cases: four phenotypically identical and 13 with 1-4 HLA mismatches. The conditioning regimen generally consisted of busulphan 600 mg/m(2) plus cyclophosphamide (Endoxan) 260 mg/kg and cyclosporin with methotrexate for GvHD prophylaxis. Rabbit anti-thymocyte globulin (Thymoglobuline) was given for all unrelated or familial mismatched transplantations. The median nucleated cell dose infused was 6.00 x 10(8) TNC/kg. No bone marrow (apart from one) was T cell depleted. For first transplants, engraftment was observed in 23/27 patients (pts) (85%). Primary graft failure was observed in 4/27 patients (16%), two were retransplanted from an unrelated donor, one with success. Four patients have died. The primary cause of death was infection in three cases (TRM : 11%) and disease progression in one case, after primary graft failure. Of the 23 living patients, two have disease progression after graft failure and 21 (78%) have functional grafts with a favourable long-term outcome after a median follow-up of 4.7 years, having either full or mixed chimaerism. Among surviving patients with functional grafts, 13 (62%) were transplanted from unrelated donors of whom 10 (77 %) had HLA disparities. There was a remarkably low incidence of GvHD. In our experience, haematopoietic stem cell transplantation using an HLA-matched familial donor or an HLA-matched or -mismatched unrelated donor without T cell depletion or irradiation can achieve a favourable outcome in Hurler's syndrome, with improved cognitive function, but with a limited effect on the corneas and skeleton.