Metachromatic Leukodystrophy (MLD) is a rare, fatal demyelinating disorder with limited treatment options. Published outcomes after hematopoietic stem cell transplantation (HSCT) are scant and mixed. We report survival and function following HSCT for a large, single-center MLD cohort. Transplant-related data, survival and serial measures (brain MRI, nerve conduction velocity (NCV), neurologic and neuropsychology evaluations) were reviewed. When possible, parental interviews informed current neurologic status, quality-of-life, and adaptive functioning. Gross motor and expressive functions for late-infantile (LI-MLD) and juvenile (J-MLD) patients were described using previously reported, MLD-specific scales. Forty patients with confirmed MLD have undergone HSCT at our center. Twenty-one (53 %) survive at a median 12 years post-HSCT. Most deaths (n = 17) were treatment-related; two died from disease progression. Survival did not depend upon MLD subtype or symptom status at transplant. LI-MLD patients survive beyond reported life expectancy in untreated disease. Abnormal brain MRI and peripheral nerve conduction velocities (NCV) were common before HSCT. Following transplant, fewer patients experienced MRI progression compared to NCV deterioration. Sixteen LI-MLD and J-MLD survivors were evaluable for long-term gross motor and/or expressive language functioning using existing MLD clinical scoring systems. While most J-MLD patients regressed, the aggregate cohort demonstrated superior retention of function compared to published natural history. Seventeen LI-MLD, J-MLD and adult subtype (A-MLD) survivors were evaluable for long-term adaptive functioning, activities of daily living, and/or cognition. Relative cognitive sparing was observed despite overall global decline. Five sibling pairs (one LI-MLD and four J-MLD), in which at least one underwent transplant in our cohort, were evaluable. Within each familial dyad, survival or function was superior for the treated sibling, or if both siblings were transplanted, for the pre-symptomatic sibling. HSCT is a viable treatment option for MLD, but has significant limitations. Later-onset phenotypes may benefit most from early, pre-symptomatic transplant. Until superior, novel treatment strategies are demonstrated, MLD patients should be carefully considered for HSCT.

Pathogenic variants in the ABCD1 gene cause adrenoleukodystrophy (ALD), a progressive metabolic disorder characterized by 3 core clinical syndromes: a slowly progressive myeloneuropathy, a rapidly progressive inflammatory leukodystrophy (cerebral ALD), and primary adrenal insufficiency. These syndromes are not present in all individuals and are not related to genotype. Cerebral ALD and adrenal insufficiency require early detection and intervention and warrant clinical surveillance because of variable penetrance and age at onset. Newborn screening has increased the number of presymptomatic individuals under observation, but clinical surveillance protocols vary. We used a consensus-based modified Delphi approach among 28 international ALD experts to develop best-practice recommendations for diagnosis, clinical surveillance, and treatment of patients with ALD. We identified 39 discrete areas of consensus. Regular monitoring to detect the onset of adrenal failure and conversion to cerebral ALD is recommended in all male patients. Hematopoietic cell transplant (HCT) is the treatment of choice for cerebral ALD. This guideline addresses a clinical need in the ALD community worldwide as the number of overall diagnoses and presymptomatic individuals is increasing because of newborn screening and greater availability of next-generation sequencing. The poor ability to predict the disease course informs current monitoring intervals but remains subject to change as more data emerge. This knowledge gap should direct future research and illustrates once again that international collaboration among physicians, researchers, and patients is essential to improving care.

Cerebral adrenoleukodystrophy (CALD) is a rapidly progressing, often fatal neurodegenerative disease caused by mutations in the ABCD1 gene, resulting in deficiency of ALD protein. Clinical benefit has been reported following allogeneic hematopoietic stem cell transplantation (HSCT). We conducted a large multicenter retrospective chart review to characterize the natural history of CALD, to describe outcomes after HSCT, and to identify predictors of treatment outcomes. Major functional disabilities (MFDs) were identified as having the most significant impact on patients' abilities to function independently and were used to assess HSCT outcome. Neurologic function score (NFS) and Loes magnetic resonance imaging score were assessed. Data were collected on 72 patients with CALD who did not undergo HSCT (untreated cohort) and on 65 patients who underwent transplantation (HSCT cohort) at 5 clinical sites. Kaplan-Meier (KM) estimates of 5-year overall survival (OS) from the time of CALD diagnosis were 55% (95% confidence interval [CI], 42.2% to 65.7%) for the untreated cohort and 78% (95% CI, 64% to 86.6%) for the HSCT cohort overall (P = .01). KM estimates of 2-year MFD-free survival for patients with gadolinium-enhanced lesions (GdE+) were 29% (95% CI, 11.7% to 48.2%) for untreated patients (n = 21). For patients who underwent HSCT with GdE+ at baseline, with an NFS ≤1 and Loes score of 0.5 to ≤9 (n = 27), the 2-year MFD-free survival was 84% (95% CI, 62.3% to 93.6%). Mortality rates post-HSCT were 8% (5 of 65) at 100days and 18% (12 of 65) at 1 year, with disease progression (44%; 7 of 16) and infection (31%; 5 of 16) listed as the most common causes of death. Adverse events post-HSCT included infection (29%; 19 of 65), acute grade II-IV graft-versus-host disease (GVHD) (31%; 18 of 58), and chronic GVHD (7%; 4 of 58). Eighteen percent of the patients (12 of 65) experienced engraftment failure after their first HSCT. Positive predictors of OS in the HSCT cohort may include donor-recipient HLA matching and lack of GVHD, and early disease treatment was predictive of MFD-free survival. GdE+ status is a strong predictor of disease progression in untreated patients.‎ This study confirms HSCT as an effective treatment for CALD when performed early. We propose survival without MFDs as a relevant treatment goal, rather than solely assessing OS as an indicator of treatment success.

Mucopolysaccharidosis type I (MPS I) is a rare autosomal recessive inherited disease, caused by deficiency of the enzyme α-L-iduronidase, resulting in accumulation of the glycosaminoglycans (GAGs) dermatan and heparan sulfate in organs and tissues. If untreated, patients with the severe phenotype die within the first decade of life. Early diagnosis is crucial to prevent the development of fatal disease manifestations, prominently cardiac and respiratory disease, as well as cognitive impairment. However, the initial symptoms are nonspecific and impede early diagnosis. This review discusses common phenotypic manifestations in the order in which they develop. Similarities and differences in the three animal models for MPS I are highlighted. Earliest symptoms, which present during the first 6 months of life, include hernias, coarse facial features, recurrent rhinitis and/or upper airway obstructions in the absence of infection, and thoracolumbar kyphosis. During the next 6 months, loss of hearing, corneal clouding, and further musculoskeletal dysplasias develop. Finally, late manifestations including lower airway obstructions and cognitive decline emerge. Cardiac symptoms are common in MPS I and can develop in infancy. The underlying pathogenesis is in the intra- and extracellular accumulation of partially degraded GAGs and infiltration of cells with enlarged lysosomes causing tissue expansion and bone deformities. These interfere with the proper arrangement of collagen fibrils, disrupt nerve fibers, and cause devastating secondary pathophysiological cascades including inflammation, oxidative stress, and other disruptions to intracellular and extracellular homeostasis. A greater understanding of the natural history of MPS I will allow early diagnosis and timely management of the disease facilitating better treatment outcomes.

Cerebral adrenoleukodystrophy is a severe form of X-linked adrenoleukodystrophy characterized by white-matter disease, loss of neurologic function, and early death. Elivaldogene autotemcel (eli-cel) gene therapy, which consists of autologous CD34+ cells transduced with Lenti-D lentiviral vector containing ABCD1 complementary DNA, is being tested in persons with cerebral adrenoleukodystrophy. In a phase 2-3 study, we evaluated the efficacy and safety of eli-cel therapy in boys with early-stage cerebral adrenoleukodystrophy and evidence of active inflammation on magnetic resonance imaging (MRI). The primary efficacy end point was survival without any of six major functional disabilities at month 24. The secondary end points included overall survival at month 24 and the change from baseline to month 24 in the total neurologic function score. A total of 32 patients received eli-cel; 29 patients (91%) completed the 24-month study and are being monitored in the long-term follow-up study. At month 24, none of these 29 patients had major functional disabilities; overall survival was 94%. At the most recent assessment (median follow-up, 6 years), the neurologic function score was stable as compared with the baseline score in 30 of 32 patients (94%); 26 patients (81%) had no major functional disabilities. Four patients had adverse events that were directly related to eli-cel. Myelodysplastic syndrome (MDS) with excess blasts developed in 1 patient at month 92; the patient underwent allogeneic hematopoietic stem-cell transplantation and did not have MDS at the most recent follow-up. At a median follow-up of 6 years after lentiviral gene therapy, most patients with early cerebral adrenoleukodystrophy and MRI abnormalities had no major functional disabilities. However, insertional oncogenesis is an ongoing risk associated with the integration of viral vectors. (Funded by Bluebird Bio; ALD-102 and LTF-304 ClinicalTrials.gov numbers NCT01896102 and NCT02698579, respectively.).

Mucopolysaccharidosis type I (MPS I) is a lysosomal disease, caused by a deficiency of the enzyme alpha-L-iduronidase (IDUA). IDUA catalyzes the degradation of the glycosaminoglycans dermatan and heparan sulfate (DS and HS, respectively). Lack of the enzyme leads to pathologic accumulation of undegraded HS and DS with subsequent disease manifestations in multiple organs. The disease can be divided into severe (Hurler syndrome) and attenuated (Hurler-Scheie, Scheie) forms. Currently approved treatments consist of enzyme replacement therapy (ERT) and/or hematopoietic stem cell transplantation (HSCT). Patients with attenuated disease are often treated with ERT alone, while the recommended therapy for patients with Hurler syndrome consists of HSCT. While these treatments significantly improve disease manifestations and prolong life, a considerable burden of disease remains. Notably, treatment can partially prevent, but not significantly improve, clinical manifestations, necessitating early diagnosis of disease and commencement of treatment. This review discusses these standard therapies and their impact on common disease manifestations in patients with MPS I. Where relevant, results of animal models of MPS I will be included. Finally, we highlight alternative and emerging treatments for the most common disease manifestations.