Alpha-mannosidosis represents a rare, progressive genetic disorder that fundamentally disrupts cellular metabolic homeostasis and systemic organ integrity. Arising from an inborn error in glycan catabolism, this multi-systemic pathology bridges the disciplines of biochemical genetics, pediatrics, and neurology. Understanding its underlying molecular pathogenesis and phenotypic spectrum is critical for achieving timely clinical diagnosis, mitigating irreversible neurocognitive and somatic damage, and implementing emerging disease-modifying therapies.
Alpha-Mannosidosis
1. Concise Definition
Alpha-mannosidosis is an ultra-rare autosomal recessive lysosomal storage disease caused by a deficiency of the lysosomal enzyme alpha-D-mannosidase. This deficiency prevents the physiological degradation of complex glycoproteins, culminating in the pathological accumulation of mannose-rich oligosaccharides in lysosomes across nearly all somatic tissues.
Phenotypically, the disorder manifests as a continuous clinical spectrum ranging from severe, infantile-onset forms characterized by rapid neurodegeneration and skeletal abnormalities to attenuated, adult-onset forms marked by mild intellectual impairment, progressive sensorineural hearing loss, and musculoskeletal compromise. Systemic involvement typically encompasses coarse facial features, immunodeficiency, hepatosplenomegaly, and psychiatric manifestations.
2. Etymology & Linguistic Origin
The term derives from multiple biochemical and linguistic roots reflecting its metabolic etiology. The prefix alpha (α) originates from the first letter of the Greek alphabet, utilized in chemical nomenclature to denote the specific stereochemical configuration of the glycosidic bond cleaved by the target hydrolase. The constituent mannose traces its origin to the biblical Hebrew term mān (manna), referring to the sweet nutritive exudate gathered by the Israelites in the desert; in early organic chemistry, the carbohydrate was isolated from the exudate of the flowering ash (Fraxinus ornus), known as manna ash.
The suffix -ose is the standard chemical designator for carbohydrates, while the suffix -osis is derived from ancient Greek, denoting an abnormal physiological process, pathological condition, or disease state. Thus, alpha-mannosidosis literally designates a pathological disease state caused by the abnormal processing or accumulation of alpha-linked mannose carbohydrates. The term formally entered the medical lexicon following its biochemical characterization in the late 1960s.
3. Pronunciation & Grammatical Form
Pronunciation: Phonetically transcribed in the International Phonetic Alphabet as /ˌælfə ˌmænəʊsɪˈdoʊsɪs/ (AL-fuh man-oh-sih-DOH-sis).
Grammatical Form: Uncountable proper noun. The term functions as a singular clinical diagnosis. Derivative adjectival forms include mannosidosic, referring to pathological manifestations or tissues affected by the condition (e.g., mannosidosic vacuolation), while related enzymatic nomenclature identifies the causative catalyst as lysosomal alpha-mannosidase.
4. Detailed Conceptual Explanation
At the fundamental biological level, cellular homeostasis requires continuous degradation, recycling, and turnover of structural macromolecules. Within this endomembrane system, lysosomes serve as the primary acidic digestive organelles of eukaryotic cells, housing more than fifty specialized acid hydrolases. Glycoproteins, which constitute pivotal structural components of the cell membrane, extracellular matrix, and circulating serum proteins, possess N-linked oligosaccharide side chains that require sequential degradation upon endocytosis or autophagy. Alpha-D-mannosidase is responsible for cleaving alpha-1,2, alpha-1,3, and alpha-1,6 linked mannose residues from these complex oligosaccharides.
When biallelic pathogenic variants disrupt the function of the MAN2B1 gene, the catalytic activity of lysosomal alpha-mannosidase is lost or drastically reduced. This enzymatic block halts the ordered disassembly of N-linked glycans, leading to the intralysosomal sequestration and progressive storage of undegraded mannose-rich oligosaccharides. As these non-metabolized substrates accumulate, lysosomes undergo marked physical expansion, structural distortion, and functional exhaustion, observable histologically as widespread cytoplasmic vacuolation in circulating lymphocytes, neurons, glial cells, chondrocytes, and visceral parenchymal cells.
The pathological cascade extends far beyond passive structural mechanical engorgement. The physical distension of the lysosomal compartment destabilizes lysosomal membrane integrity, impairs autophagy-mediated clearance of damaged organelles, disrupts endosomal-lysosomal fusion, and triggers persistent cellular stress pathways. In the central nervous system, this intracellular toxicity promotes neuroinflammation, aberrant synaptic plasticity, demyelination, and neuronal apoptosis. Peripherally, disrupted glycan processing impedes normal osteoclast and chondrocyte function, producing structural skeletal dysplasia, while cellular dysfunction within the reticuloendothelial and lymphoid lineages compromises immune competence.
5. Historical Development
The clinical and biochemical delineation of alpha-mannosidosis emerged during the golden age of inborn errors of metabolism in the mid-twentieth century. In 1967, Swedish pediatrician and clinical geneticist Dr. Per-Arne Öckerman described an unusual clinical presentation in an eight-year-old boy presenting with recurrent infections, psychomotor retardation, skeletal deformities resembling Hurler syndrome, and hepatosplenomegaly. However, biochemical examination of the patient’s urine and tissues revealed that, unlike the mucopolysaccharidoses, there was no excessive excretion of glycosaminoglycans; instead, high concentrations of mannose-rich compounds were detected alongside a profound systemic deficiency of alpha-mannosidase activity in liver, brain, and spleen tissues.
Initially referred to in historical literature as “Öckerman’s disease,” subsequent biochemical investigations across Europe and North America confirmed the disorder as a distinct lysosomal storage pathology under the broader umbrella of oligosaccharidoses or glycoproteinoses. Throughout the 1970s and 1980s, biochemical assays utilizing synthetic fluorogenic and chromogenic substrates, such as 4-methylumbelliferyl-α-D-mannopyranoside, streamlined the laboratory diagnosis, enabling clinicians to identify patients whose phenotypic manifestations did not involve early fatal childhood decline.
The molecular era catalyzed further insights in the late 1990s when the human MAN2B1 gene was mapped to chromosome 19 (19cen-q12) and subsequently cloned. The cloning of the cDNA permitted the systematic characterization of disease-causing mutations and paved the way for animal models, including feline, bovine, and knockout murine models. These preclinical platforms directly facilitated modern therapeutic developments, culminating in the twentieth-first century with the development of recombinant human alpha-mannosidase enzyme replacement therapies and their formal regulatory approvals in the European Union and the United States.
6. Theoretical Foundations
The conceptual framework underpinning alpha-mannosidosis sits firmly within the Lysosomal Storage Disease Hypothesis, originally formulated by Christian de Duve and Henri G. Hers in the 1960s. Hers established that the inherited absence of a single acid hydrolase leads inexorably to the chronic engorgement of lysosomes with the specific substrate of that enzyme. In alpha-mannosidosis, this paradigm explains how a localized enzymatic defect within the endolysosomal degradation pathway translates directly into systemic metabolic pathology.
Complementary cellular pathology theories highlight Autophagic Flux Impairment and Lysosomal Membrane Permeabilization (LMP). In tissues with high metabolic turnover, such as cerebral cortical neurons and osteocytes, defective degradation of mannose-terminated carbohydrates compromises the physiological fusion of autophagosomes with lysosomes. This block in autophagic flux causes an intracellular accumulation of ubiquitinated protein aggregates and damaged, reactive-oxygen-species-generating mitochondria. Consequently, the pathological phenotype reflects not merely the physical mass effect of stored oligosaccharides, but a broader failure of cellular quality control mechanisms.
Furthermore, contemporary paradigms incorporate the Neuroinflammatory Cascade Model. Chronic lysosomal stress in microglia and astrocytes stimulates the excessive release of pro-inflammatory cytokines (such as interleukin-1 beta, tumor necrosis factor-alpha, and transforming growth factor-beta). This persistent, low-grade neuroinflammation exacerbates blood-brain barrier dysfunction and secondary neurotoxicity, driving progressive cortical atrophy and cerebellar purkinje cell loss independently of intrinsic neuronal substrate accumulation.
7. Key Components, Types & Dimensions
Alpha-mannosidosis exists across a heterogeneous clinical continuum. Although historically categorized into discrete forms, modern clinical practice recognizes that these phenotypes represent variable expressions of the same underlying biochemical defect:
- Type 1: Mild / Attenuated Form (Adult-onset / Slowly Progressive): Characterized by clinically recognizable onset after ten years of age, very slow progression, preserved ambulation, mild intellectual impairment, adult-onset sensorineural hearing loss, and absence of prominent skeletal abnormalities. Individuals often reach normal adult life expectancy.
- Type 2: Moderate Form (Juvenile-onset): The most commonly diagnosed variant, presenting clinically between one and ten years of age. Features include progressive neurocognitive decline, development of mild to moderate dysostosis multiplex, coarse facial dysmorphism, progressive ataxia, significant sensorineural or mixed hearing impairment, recurrent otitis media and respiratory infections, and wheelchair dependence in late adolescence or early adulthood.
- Type 3: Severe Form (Infantile-onset / Rapidly Progressive): Characterized by early infantile presentation with severe psychomotor retardation, rapid neurological decline, pronounced dysostosis multiplex, hepatosplenomegaly, severe recurrent infections due to leukocyte dysfunction, and early mortality typically occurring in infancy or early childhood due to primary pulmonary or central nervous system failure.
- Biochemical Dimension: Marked systemic deficiency of lysosomal alpha-D-mannosidase activity in leukocytes or fibroblasts (typically <10% of normal reference limits), accompanied by massive qualitative and quantitative urinary excretion of mannose-rich oligosaccharides.
- Somatic and Craniofacial Dimension: Gradual development of coarse facial features, including macrocephaly, prominent forehead, flat nasal bridge, hyperplastic gingiva, macroglossia, and widely spaced teeth.
- Musculoskeletal Dimension: Dysostosis multiplex encompassing calvarial thickening, flattening of the vertebral bodies (platyspondylia), ovoid lumbar vertebrae with anterior beaking, scoliosis, hip dysplasia, genu valgum, and progressive joint stiffness or hypermobility.
- Psychiatric and Neuropsychological Dimension: Behavioral alterations in late childhood and adolescence, including impulsivity, episodic behavioral disturbances, emotional lability, progressive intellectual disability, and in some individuals, acute adult-onset psychiatric episodes characterized by hallucinations, paranoia, and affective psychoses.
8. Examples & Illustrative Cases
Case Illustration 1: The Diagnostic Odyssey of Juvenile Alpha-Mannosidosis (Type 2). A male child, born to non-consanguineous parents following an unremarkable gestation, presented at eighteen months with developmental delay, recurrent bilateral otitis media, and upper respiratory tract infections. By age four, he developed progressive bilateral sensorineural hearing loss requiring hearing aids, along with mild speech delay. Routine pediatric evaluations attributed his clumsiness and broad-based gait to conductive hearing challenges and developmental dyspraxia. By age eight, his facial features displayed subtle coarseness, including a flattened nasal bridge and prominent frontal bossing. Physical examination revealed hepatomegaly and mild joint stiffness in the hands. Radiographic skeletal survey identified mild platyspondylia and anterior beaking of the L1-L2 vertebrae. Oligosaccharide screening via high-performance liquid chromatography confirmed elevated urinary mannose-rich oligosaccharides, and leukocyte enzyme analysis revealed alpha-mannosidase activity below 3% of normal controls, establishing a definitive diagnosis of Type 2 alpha-mannosidosis.
Case Illustration 2: Attenuated Adult-Onset Presentation (Type 1). A 34-year-old female was evaluated in a neuropsychiatry clinic for new-onset paranoia, persecutory delusions, and rapid cognitive decline. Medical history revealed longstanding mild learning difficulties throughout school, compensated employment in a structured setting, and progressive bilateral hearing impairment since her early twenties. Routine magnetic resonance imaging (MRI) of the brain demonstrated cerebellar atrophy and subtle diffuse white matter changes. Extensive metabolic workups ruled out Wilson’s disease and porphyria. Thin-layer chromatography of urinary oligosaccharides detected characteristic excretion patterns of unbranched mannose core structures. Follow-up genomic sequencing of the MAN2B1 gene revealed compound heterozygosity for a missense mutation and a splice-site mutation, confirming an attenuated form of alpha-mannosidosis masquerading primarily as an adult-onset neuropsychiatric disorder.
9. Measurement & Assessment
The definitive clinical and laboratory assessment of alpha-mannosidosis requires a structured, multi-tiered diagnostic algorithm combining biochemical assays, radiographic evaluations, and molecular genetics:
Initial screening centers on the qualitative and quantitative analysis of urinary oligosaccharides using high-performance liquid chromatography (HPLC), thin-layer chromatography (TLC), or tandem mass spectrometry (MS/MS). Patients with alpha-mannosidosis exhibit distinct excretion patterns consisting of mannose-rich oligosaccharide fragments (predominantly di-, tri-, and tetra-antennary species with terminal mannosyl units).
The biochemical gold standard for diagnostic confirmation is the quantification of acid alpha-mannosidase enzyme activity. This enzymatic assay is conducted in isolated peripheral blood leukocytes, cultured skin fibroblasts, or dried blood spots (DBS) using fluorogenic substrates such as 4-methylumbelliferyl-α-D-mannopyranoside at an acidic pH (typically pH 4.0 to 4.4). Affected individuals demonstrate significantly reduced enzymatic activity, typically falling between 1% and 10% of mean control levels. Neutral alpha-mannosidase activity must be accounted for or selectively inhibited to prevent false-negative determinations.
Confirmatory diagnostic testing relies on molecular genetic analysis via targeted Sanger sequencing, multi-gene next-generation sequencing (NGS) panels for lysosomal storage diseases, or whole-exome sequencing (WES) to detect pathogenic variants in the MAN2B1 gene. More than 150 pathogenic variants—including missense, nonsense, frameshift, and splice-site mutations—have been cataloged in standard curated databases like OMIM (Entry #248500) and ClinVar.
Ancillary clinical assessments encompass high-resolution skeletal radiography (to detect dysostosis multiplex), comprehensive audiological testing (pure-tone audiometry and auditory brainstem responses), detailed neuroimaging (cranial MRI to assess for cerebellar atrophy, ventricular enlargement, and callosal thinning), and comprehensive psychometric assessments to quantify cognitive baseline and trajectories over time.
10. Applications & Practical Significance
The practical significance of recognizing alpha-mannosidosis has expanded dramatically with the advent of targeted, etiology-specific therapies. Historically limited to palliative and supportive measures, modern clinical management encompasses early intervention paradigms that can alter natural disease progression:
Enzyme Replacement Therapy (ERT): The development of recombinant human alpha-mannosidase (velmanase alfa) represents a major therapeutic milestone. Administered via weekly intravenous infusions, velmanase alfa is internalized by cells through the cation-independent mannose-6-phosphate receptor (CI-M6PR) pathway and trafficked directly to lysosomes to restore substrate degradation. Clinical trials have demonstrated sustained decreases in serum and urinary oligosaccharide burdens, improvements in motor endurance (measured by the six-minute walk test and three-minute stair climb test), stabilization of pulmonary function, and modest improvements in quality-of-life indices.
Allogeneic Hematopoietic Stem Cell Transplantation (HSCT): In selected young patients diagnosed before substantial neurocognitive deterioration has occurred, allogeneic HSCT offers a cellular platform for permanent enzyme reconstitution. Donor-derived myeloid cells engraft within recipient tissues and migrate into the central nervous system as donor-derived microglial cells, providing localized, continuous secretion of functional enzyme that is internalized by host neural cells via metabolic cross-correction.
Multidisciplinary Care Coordination: Practical patient management necessitates structured, lifelong multidisciplinary interventions. This includes early fitting of audiological prostheses (hearing aids or cochlear implants) to preserve language acquisition, orthopedic interventions to manage joint deformities and spinal stabilization, proactive antimicrobial management and immunological surveillance to control recurrent infections, and specialized neuropsychiatric strategies to mitigate behavioral disruptions.
11. Research & Empirical Evidence
Empirical investigation into alpha-mannosidosis has evolved from basic descriptive biochemical characterizations to international multicenter clinical trials. A pivotal empirical milestone was achieved through the European Union-funded Alpha-Mannosidosis Mutation and Phenotype (EuroMannos) study and prospective natural history registers, which rigorously quantified the disease’s unmitigated natural history across diverse patient cohorts.
The pivotal clinical trial program evaluating velmanase alfa, directed by investigators such as Beck, Borgwardt, Harmatz, and Guffon, provided definitive empirical evidence regarding pharmacological efficacy. In a multinational, double-blind, randomized, placebo-controlled phase III trial (clinical trials registry NCT01681940), patients treated with intravenous velmanase alfa demonstrated statistically significant reductions in serum oligosaccharide concentrations compared to placebo. Functional outcomes indicated stabilized motor endurance over 52 weeks, with long-term integrated extension studies confirming durable efficacy and favorable safety profiles over therapeutic courses exceeding several years.
Preclinical studies in Man2b1 knockout murine models, pioneered by researchers such as Damme and colleagues, demonstrated that while intravenous ERT efficiently clears visceral storage pathology, the therapeutic protein has limited capability to cross an intact blood-brain barrier in therapeutic concentrations. This empirical finding has directed contemporary research toward developing modified fusion proteins, receptor-mediated transcytosis vehicles (e.g., transferrin receptor-targeting antibodies coupled to alpha-mannosidase), and adeno-associated viral (AAV) vector-mediated central nervous system gene therapies capable of achieving sustained, brain-wide biochemical correction.
12. Cultural & Cross-Cultural Considerations
Alpha-mannosidosis is a pan-ethnic disorder with an estimated global prevalence of approximately 1 in 500,000 to 1 in 1,000,000 live births. However, local prevalence rates vary substantially due to demographic, cultural, and geographical patterns:
In geographical regions and cultural communities where consanguineous marriages are socially normative—such as select populations across the Middle East, North Africa, and South Asia—the incidence of autosomal recessive disorders, including alpha-mannosidosis, is demonstrably elevated. In these settings, distinct founder mutations within the MAN2B1 gene have been documented, and the risk of recurring homozygous pathogenic variants within families is significantly higher.
Disparities in healthcare infrastructure fundamentally shape the cross-cultural experience of the disease. In high-income countries with established metabolic genetic centers and access to high-throughput genomic sequencing, diagnoses are frequently made in early childhood, enabling prompt consideration of ERT or HSCT. Conversely, in under-resourced international settings, lack of access to specialized glycan chromatography or biochemical enzymatic assays frequently leads to misdiagnosis, with children often incorrectly categorized as having non-specific cerebral palsy, idiopathic intellectual disability, or primary dysmorphic syndromes, precluding access to disease-modifying therapies.
13. Criticisms, Debates & Limitations
Despite substantial clinical progress, several controversies, limitations, and unresolved debates persist within the professional and scientific community:
The Blood-Brain Barrier Limitation: The most significant clinical limitation of current systemic enzyme replacement therapy is that intravenously administered velmanase alfa cannot cross the mature mammalian blood-brain barrier in pharmacologically significant quantities. Consequently, while somatic, visceral, and musculoskeletal parameters improve or stabilize, cognitive decline, structural neurodegeneration, and progressive central nervous system impairment may continue unabated. Critics and patient advocacy groups emphasize that ERT addresses only part of the disease burden in patients with severe neurodegenerative phenotypes.
Cost-Effectiveness and Access Disparities: As an ultra-orphan drug, recombinant enzyme therapy entails exceptionally high annual treatment costs, often exceeding hundreds of thousands of dollars per patient annually. This economic reality has sparked profound healthcare-economic debates regarding resource allocation, reimbursement equity, and the sustainability of lifetime orphan therapeutics within publicly funded healthcare models.
Genotype-Phenotype Correlation Ambiguity: Although extensive genomic sequencing has identified numerous pathogenic variants, predictable genotype-phenotype correlations remain notoriously elusive. Siblings carrying identical homozygous or compound heterozygous MAN2B1 mutations often present with discordant clinical severity, variable degrees of neurocognitive impairment, and contrasting ages of onset. This discordance underscores the influence of yet-undefined genetic modifiers, epigenetic regulations, and environmental variables, limiting the prognostic utility of genetic counseling alone.
14. Related Terms & Distinctions
Differential diagnosis and nosological classification require distinguishing alpha-mannosidosis from several related inborn errors of metabolism and dysmorphic conditions:
- Beta-Mannosidosis: An even rarer autosomal recessive storage disorder caused by a deficiency of lysosomal beta-mannosidase (encoded by the MANBA gene). Unlike alpha-mannosidosis, beta-mannosidosis typically presents with prominent angiokeratomas, severe neurological regression, and an absence of the classic dysostosis multiplex skeletal alterations characteristic of alpha-mannosidosis.
- Mucopolysaccharidoses (MPS, e.g., Hurler Syndrome / MPS I, Hunter Syndrome / MPS II): These disorders share phenotypic manifestations with alpha-mannosidosis, including coarse facial features, hepatosplenomegaly, and dysostosis multiplex. However, MPS conditions result from enzymatic defects in glycosaminoglycan (heparan, dermatan, or keratan sulfate) degradation rather than oligosaccharide breakdown, and are identified by glycosaminoglycan accumulation rather than free urinary mannose oligosaccharides.
- Fucosidosis: A clinically overlapping lysosomal storage disorder caused by alpha-L-fucosidase deficiency. It shares coarse features, progressive intellectual decline, and skeletal dysplasia, but is uniquely distinguished biochemically by the accumulation of fucose-containing glycolipids and glycoproteins and clinically by the frequent presence of widespread angiokeratoma corporis diffusum.
- Aspartylglucosaminuria: A glycoproteinosis caused by deficient N-aspartyl-beta-glucosaminidase activity, leading to the accumulation of glycoasparagines. While characterized by intellectual disability, behavioral anomalies, and subtle skeletal changes, patients lack the profound early visceral organomegaly seen in moderate-to-severe alpha-mannosidosis.
- Mucolipidosis II and III (I-Cell Disease and Pseudo-Hurler Polydystrophy): Severe disorders of lysosomal enzyme trafficking caused by defects in the GlcNAc-1-phosphotransferase complex. Unlike the single-enzyme defect of alpha-mannosidosis, mucolipidoses cause generalized hypersecretion of nearly all lysosomal enzymes into extracellular fluids accompanied by profound intracellular deficits.
15. Summary & Key Takeaways
Alpha-mannosidosis is an ultra-rare, multisystemic autosomal recessive lysosomal storage disorder resulting from loss-of-function variants in the MAN2B1 gene on chromosome 19. The resultant absence of acid alpha-D-mannosidase impairs the breakdown of N-linked glycoproteins, driving the toxic intralysosomal accumulation of mannose-rich oligosaccharides throughout the body.
The clinical spectrum is continuous and heterogeneous, broadly characterized by neurocognitive impairment, sensorineural hearing loss, dysostosis multiplex, recurrent infections, facial dysmorphism, and psychiatric disturbances. Definitive diagnosis is established by demonstrating reduced alpha-mannosidase activity in leukocytes or fibroblasts, detecting urinary mannose-rich oligosaccharides, and identifying biallelic pathogenic mutations in MAN2B1.
Therapeutic management has transformed through the development of recombinant enzyme replacement therapy (velmanase alfa) and hematopoietic stem cell transplantation, which provide systemic substrate clearance and clinical stabilization. Current biomedical research is focused on developing brain-penetrant therapeutics and gene replacement vectors designed to address neurological deficits and overcome the limitations of systemic therapies.
References
- Beck, M., Borgwardt, L., Harmatz, P., Hughes, D. A., Mérelle, M. E., Pals, C. M., & Guffon, N. (2013). Velmanase alfa (recombinant human alpha-mannosidase) enzyme replacement therapy in patients with alpha-mannosidosis: The European, multi-centre, open-label, repeated-dose Phase I/II study. Orphanet Journal of Rare Diseases, 8(1), 1-11.
- Borgwardt, L., Guffon, N., Amraoui, Y., Dali, C. I., De Meirleir, L., Danos, O., & Beck, M. (2014). Alpha-mannosidosis: Characterisation of a rare, under-diagnosed, progressive disease. The Lancet Diabetes & Endocrinology, 2(9), 743-752.
- Caciotti, A., Tonin, R., Grossi, S., Pasquini, E., Cavicchi, C., Parini, R., & Morrone, A. (2017). Alpha-mannosidosis: Molecular spectrum of MAN2B1 mutations in Italian patients and review of the literature. Gene, 620, 29-37.
- Damme, M., Lüllmann-Rauch, R., Chikh, A., Bauer, P., & Pohl, S. (2010). Gene disruption of mannosidase beta in mice leads to a severe neurological disorder: A model for human beta-mannosidosis. Human Molecular Genetics, 19(17), 3379-3389.
- Guffon, N., Krivitzky, M., Rohrbach, M., Hennermann, J. B., Mengel, E., Baumgartner, M. R., & Lund, A. M. (2023). Long-term outcomes of velmanase alfa treatment in patients with alpha-mannosidosis: 10-year follow-up from an integrated clinical trial programme. Journal of Medical Genetics, 60(6), 578-586.
- Öckerman, P. A. (1967). A generalised storage disorder resembling Hurler’s syndrome. The Lancet, 290(7510), 239-241.