An unusual diagnosis of alpha-mannosidosis with ocular anomalies: Behind the scenes of a hidden copy number variation

Alpha-mannosidosis is a rare autosomal recessive lysosomal storage disorder caused by biallelic mutations in the MAN2B1 gene and characterized by a wide clinical heterogeneity. Diagnosis for this multisystemic disorder is confirmed by the presence of either a deficiency in the lysosomal enzyme acid alpha-mannosidase or biallelic mutations in the MAN2B1 gene. This diagnosis confirmation is crucial for both clinical management and genetic counseling purposes. Here we describe a late diagnosis of alpha-mannosidosis in a patient presenting with syndromic intellectual disability, and a rare retinopathy, where reverse phenotyping played a pivotal role in interpreting the exome sequencing result. While a first missense variant was classified as a variant of uncertain significance, the phenotype-guided analysis helped us detect and interpret an in-trans apparent alu-element insertion, which appeared to be a copy number variant (CNV) not identified by the CNV caller. A biochemical analysis showing abnormal excretion of urinary mannosyloligosaccharide and an enzyme assay permitted the re-classification of the missense variant to likely pathogenic, establishing the diagnosis of alpha-mannosidosis. This work emphasizes the importance of reverse phenotyping in the context of exome sequencing.

Diagnosis of alpha-Mannosidosis: Practical approaches to reducing diagnostic delays in this ultra-rare disease

Alpha-mannosidosis is an ultra-rare lysosomal disease that is caused by variants of the MAN2B1 gene on chromosome 19p13. These variants result in faulty or absent alpha-mannosidase in lysosomes, which leads to intracellular accumulation of mannose-containing oligosaccharides. Diagnosis of alpha-mannosidosis is often delayed, in part because of the rarity of the disease, its gradual onset and heterogeneity of presentation, but also because of the similarity of many signs and symptoms of the disease to those of other lysosomal diseases. Treatment of alpha-mannosidosis was previously limited to hematopoietic stem cell transplantation, but outcomes are variable and not all patients are eligible or have a suitable donor. Recently, an enzyme replacement therapy, recombinant human alpha-mannosidase (velmanase alfa), was approved for the treatment of non-neurological manifestations in adult and pediatric patients with alpha-mannosidosis. Treatment with velmanase alfa reduces serum levels of oligosaccharides, increases levels of immunoglobulin G, and improves patients' functional capacity and quality of life, although it is not effective for the neurologic phenotype because it does not cross the blood-brain barrier. Since the effects of velmanase alfa are more marked in children than adults, early diagnosis to allow early initiation of treatment has become more important. To support this, patient, parent/caregiver, and clinician awareness and education is imperative. A number of approaches can be taken to meet this goal, such as the development of disease registries, validated diagnostic algorithms, and screening tools, improved under-/post-graduate clinician education, easily accessible and reliable information for patients/families (such as that made available on the internet), and the formation of patient advocacy groups. Such approaches may raise awareness of alpha-mannosidosis, reduce the diagnostic delay and thus improve the lives of those affected.

Long-term clinical evaluation of patients with alpha-mannosidosis - A multicenter study

BACKGROUND

Alpha mannosidosis is an autosomal recessive lysosomal storage disorder caused by biallelic pathogenic variants in the MAN2B1 gene. It manifests with clinical features, including intellectual disability, hearing impairment, coarse facial appearance, skeletal anomalies, immunodeficiency, central nervous system involvement, psychiatric comorbidities, corneal opacity, and hepatosplenomegaly. This multicenter study assesses the long-term outcomes of individuals diagnosed with alpha-mannosidosis, examining demographic, clinical, laboratory, and molecular characteristics.

METHOD

Sixteen patients diagnosed with alpha-mannosidosis who presented to four pediatric metabolic units were included in the study. The patients' medical records were analyzed and data on demographics, clinical presentation and laboratory findings were recorded.

RESULTS

Of the 16 patients (6 females, 10 males) with alpha mannosidosis included in the study, the mean age at the time of diagnosis was 79.4 ± 56.1 (16-208) months, and the mean diagnosis delay time was 57.9 ± 51.9 (4-181) months. Hearing loss was the primary manifestation found in seven out of 16 patients (43.8%), followed by speech delay in 37.8%. On clinical follow-up, 87.5% of patients experienced recurrent infections, mainly in the upper respiratory tract, with 12 requiring the use of a hearing aid. Hepatomegaly was found in six out of 13 patients who received abdominal ultrasonography; two out of 12 patients who underwent echocardiography were found to have mitral valve prolapse (16.6%). Upon neurological evaluation, five patients displayed no neurological manifestation. Delayed language development was observed in nine (56.3%) patients, intellectual disability in eight (50%) patients, and hypertonicity was identified in one (6.3%) patient with the severe form of the disease. Homozygous c.2477C>A (p.Ser826Ter) and homozygous c.967G>A (p.Glu323Lys) novel variants were detected in four patients and one patient, respectively. The most common variant observed in the study was c.2477C>A (p.Ser826Ter).

CONCLUSION

The present study identified two novel MAN2B1 variants. An evaluation of the long-term outcome of alpha-mannosidosis, in which the early initiation of enzyme replacement therapy (ERT) may lead to a better clinical outcome, can permit a better analysis of the effect of ERT on the natural progression of the disease.

Long-term outcome of a cohort of Italian patients affected with alpha-Mannosidosis

Alpha-mannosidosis (MIM #248500) is an ultra-rare autosomal recessive lysosomal storage disease with multi-system involvement and a wide phenotypic spectrum. Information on long-term outcomes remains poor. We present the long-term outcomes (median, 19 years) of nine patients with alpha-mannosidosis, three females and six males, followed at a single center. The findings of the nine patients were collected from medical records and reported as mean ± SD or median, and range. The age of onset of the first symptoms ranged from 0-1 to 10 years. The diagnostic delay ranged from 2 to 22 years (median= 11 years). Coarse face, hearing, heart valves, joints, gait, language, dysarthria, psychiatric symptoms, I.Q., MRI, walking disabilities, orthopedic disturbances and surgeries showed a slow worsening over the decades. Our patients showed a slowly worsening progressive outcome over the decades. Psychiatric symptoms were present in 100% of our population and improved with the appropriate pharmacological intervention. This aspect requires attention when following up on these patients. Our description of the long-term evolution of alpha-mannosidosis patients may provide basic knowledge for understanding the effects of specific treatments.

Alpha-mannosidosis: a case with novel ultrastructural and light microscopy findings

OBJECTIVES

Alpha-mannosidosis is a rare genetic lysosomal storage condition leading to the systemic buildup of oligomannoside. Clinical presentation and associated conditions, as well as the full extent of histopathologic changes associated with this disease process, are not fully understood.

CASE PRESENTATION

We present the case of an 8-year-1-month old patient with persistent anemia and who was initially diagnosed with Celiac disease before ultimately being diagnosed with alpha-mannosidosis. As part of his diagnostic work-up, duodenal and bone marrow biopsies were examined by pathology. Duodenal biopsies showed foamy plasma cells expanding the lamina propria which triggered a workup for a genetic storage disease; features suggestive of Celiac disease which resolved on gluten-free diet were also noted by pathology. Bone marrow analysis via electron microscopy showed cytoplasmic granules and inclusions in multiple immune cell lines.

CONCLUSIONS

Alpha-mannosidosis can occur with Celiac disease and milder forms may only be suspected from incidental pathology findings. The ultrastructural bone marrow findings from this case, the first to be reported from human, show numerous disease-associated changes in multiple immune cell lines whose contribution to disease-associated immunodeficiency is unclear.

White matter alteration and cerebellar atrophy are hallmarks of brain MRI in alpha-mannosidosis

OBJECTIVE

Despite profound neurological symptomatology there are only few MRI studies focused on the brain abnormalities in alpha-mannosidosis (AM). Our aim was to characterize brain MRI findings in a large cohort of AM patients along with clinical manifestations.

METHODS

Twenty-two brain MRIs acquired in 13 untreated AM patients (8 M/5F; median age 17 years) were independently assessed by three experienced readers and compared to 16 controls.

RESULTS

Focal and/or diffuse hyperintense signals in the cerebral white matter were present in most (85%) patients. Cerebellar atrophy was common (62%), present from the age of 5 years. Progression was observed in two out of 6 patients with follow-up scans. Cortical atrophy (62%) and corpus callosum thinning (23%) were already present in a 13-month-old child. The presence of low T₂ signal intensity in basal ganglia and thalami was excluded by the normalized signal intensity profiling. The enlargement of perivascular spaces in white matter (38%), widening of perioptic CSF spaces (62%), and enlargement of cisterna magna (85%) were also observed. Diploic space thickening (100%), mucosal thickening (69%) and sinus hypoplasia (54%) were the most frequent non-CNS abnormalities.

CONCLUSION

White matter changes and cerebellar atrophy are proposed to be the characteristic brain MRI features of AM. The previously reported decreased T₂ signal intensity in basal ganglia and thalami was not detected in this quantitative study. Rather, this relative MR appearance seems to be related to the diffuse high T₂ signal in the adjacent white matter and not the gray matter iron deposition that has been hypothesized.

α-Mannosidosis - An underdiagnosed lysosomal storage disease in individuals with an 'MPS-like' phenotype

Individuals affected by alpha-Mannosidosis suffer from similar clinical symptoms such as respiratory infections, skeletal changes as patients with mucopolysaccharidoses (MPS). α-Mannosidosis is considered as an ultra-rare disorders and also diagnostic testing is often limited. With the availability of novel therapies and easy-to-access diagnostic tests (e.g. Tandem mass spectrometry) using dried blood spots for both enzymatic and genetic testing, the chance for the development of a better understanding of disease and awareness may be triggered. In a pilot study, we have investigated 1010 residual dried blood spot samples from individuals suspicious to MPS. In these study cohort, 158/1010 individuals were genetically confirmed for MPS. Additional biochemical and genetic confirmatory testing for α-mannosidases revealed four individuals with a final diagnosis of α-mannosidosis. This unexpected high number of individuals with α-mannosidosis demonstrated the urgent need of taking this rare disorder in clinical and diagnostic consideration particularly in patients suspicious to MPS.

Ultra-orphan lysosomal storage diseases: A cross-sectional quantitative analysis of the natural history of alpha-mannosidosis

Alpha-mannosidosis (OMIM 248500) is a rare lysosomal storage disorder caused by a deficiency of the enzyme alpha-mannosidase. Recently, enzyme replacement therapy was approved in the European Union for the treatment of alpha-mannosidosis, but evaluation regarding long-term efficacy and safety is hard to assess due to missing quantitative natural history data, in particular survival. We performed a quantitative analysis of published cases (N = 111) with alpha-mannosidosis. Main outcome measures were age of disease onset, diagnostic delay and survival (overall and by subgroup exploration). Residual alpha-mannosidase activity and age of onset were explored as potential predictors of survival. STROBE criteria were respected. Median age of onset was 12 months. Median diagnostic delay was 6 years. At the age of 41 years 72.3% of patients were alive (N = 111). Residual alpha-mannosidase activity (N = 34) predicted survival: Patients with a residual alpha-mannosidase activity below or equal to 4.5% of normal in fibroblasts had a median survival of 3.5 years, whereas patients with alpha-mannosidase activity above this threshold all survived during the observation period reported. Patients with age of onset above 7 years survived significantly longer than patients with age of onset below or equal to 7 years. Patient distribution was panethnic with hotspots in the United States and Germany. We defined age of onset, diagnostic delay, and survival characteristics in a global cohort of 111 patients with alpha-mannosidosis by retrospective quantitative natural history modeling. These data expand the quantitative understanding of the clinical phenotype.

Tandem mass spectrometry-based multiplex assays for α-mannosidosis and fucosidosis

Multiplex tandem mass spectrometry (MS/MS)-based enzyme activity assays for newborn screening (NBS) and diagnosis of lysosomal storage diseases (LSDs) in newborns, using dried blood spots (DBS) on newborn screening cards, have garnered much attention due to its sensitivity, high precision, and the capability to screen for an unprecedented number of diseases in a single assay. Herein we report the development of MS/MS-based enzyme assays for the diagnosis of α-mannosidosis and fucosidosis. These new protocols are able to distinguish untreated patients from random newborns, carriers and a post-bone marrow transplant patient. We have successfully multiplexed the α-mannosidosis assay with a multiplex MS/MS assay for the screening and diagnosis of other LSDs, namely Fabry, Pompe, MPS I, Gaucher, Niemann-Pick-A/B, and Krabbe diseases. Additionally, we also multiplexed the fucosidosis NBS assay with a 5-plex assay that tests for MPS-II, MPS-IIIB, MPS-IVA, MPS-VI and MPS-VII.

Recognition of alpha-mannosidosis in paediatric and adult patients: Presentation of a diagnostic algorithm from an international working group

Alpha-mannosidosis is an ultra-rare progressive lysosomal storage disorder caused by deficiency of alpha-mannosidase. Timely diagnosis of the disease has the potential to influence patient outcomes as preventive therapies can be initiated at an early stage. However, no internationally-recognised algorithm is currently available for the diagnosis of the disease. With the aim of developing a diagnostic algorithm for alpha-mannosidosis an international panel of experts met to reach a consensus by applying the nominal group technique. Two proposals were developed for diagnostic algorithms of alpha-mannosidosis, one for patients ≤10 years of age and one for those >10 years of age. In younger patients, hearing impairment and/or speech delay are the cardinal symptoms that should prompt the clinician to look for additional symptoms that may provide further diagnostic clues. Older patients have different clinical presentations, and the presence of mental retardation and motor impairment progression and/or psychiatric manifestations should prompt the clinician to assess for other symptoms. In both younger and older patients, either additional metabolic monitoring or referral for testing is warranted upon suspicion of disease. Oligosaccharides in urine (historically performed) or serum were considered as an initial screening procedure, while enzymatic activity may also be considered as first choice in some centres. Molecular testing should be performed as a final confirmatory step. The developed algorithms can easily be applied in a variety of settings, and may help to favour early diagnosis of alpha mannosidosis and treatment.

Diffusion Tensor Imaging for Assessing Brain Gray and White Matter Abnormalities in a Feline Model of α-Mannosidosis

α-Mannosidosis (AMD) is an autosomal recessively inherited lysosomal storage disorder affecting brain function and structure. We performed ex vivo and in vivo diffusion tensor imaging (DTI) on the brains of AMD-affected cats to assess gray and white matter abnormalities. A multi-atlas approach was used to generate a brain template to process the ex vivo DTI data. The probabilistic label method was used to measure fractional anisotropy (FA), mean diffusivity, axial diffusivity, and radial diffusivity values from gray and white matter regions from ex vivo DTI. Regional analysis from various regions of the gray matter (frontal cortex, cingulate gyrus, caudate nucleus, hippocampus, thalamus, and occipital cortex), and white matter (corpus callosum, corticospinal tract, cerebral peduncle, external and internal capsule) was also performed on both ex vivo and in vivo DTI. Ex vivo DTI revealed significantly reduced FA from both gray and white matter regions in AMD-affected cats compared to controls. Significantly reduced FA was also observed from in vivo DTI of AMD-affected cats compared to controls, with lower FA values observed in all white matter regions. We also observed significantly increased axial and radial diffusivity values in various gray and white matter regions in AMD cats from both ex vivo and in vivo DTI data. Imaging findings were correlated with histopathologic analyses suggesting that DTI studies can further aid in the characterization of AMD by assessing the microstructural abnormalities in both white and gray matter.

Alpha-mannosidosis - a review of genetic, clinical findings and options of treatment

Alpha-mannosidosis (OMIM 248500) is a rare, autosomal recessive, multisystemic, progressive lysosomal storage disorder caused by a deficiency of alpha-mannosidase. It has been described in humans, cattle, domestic cats, mice and guinea pigs. In humans, alpha-mannosidosis results in progressive facial- and skeletal abnormalities, motor impairment, hearing impairment, intellectual disability, recurrent infections and immune deficiency. This review provides detailed information regarding the variability of manifestations and a description of current treatment and treatment under investigation for alpha-mannosidosis. The pathology, genetics and clinical pictures, including impairments in the activity of daily living are discussed.

Molecular diagnosis of a Chinese pedigree with α-mannosidosis and identification of a novel missense mutation

α-Mannosidosis storage disease is a rare autosomal recessive disease that is caused by a deficiency of the lysosomal enzyme α-mannosidase. In this article, a proband in China was preliminarily diagnosed as having α-mannosidosis by clinical symptoms, imaging examination, and enzyme assay. Definitive diagnosis was performed by directly sequencing the MAN2B1 gDNA and cDNA of the peripheral blood leukocyte from the patient. Finally, denaturing high-performance liquid chromatography screening, conservative analysis, and protein secondary structure prediction were used to identify the novel mutation. The results showed that the patient has compound heterozygous mutations in the MAN2B1 gene, c.856G>A (p.E286K, novel) and c.788C>T (p.P263L). Her parents are heterozygote that carry one of these two mutations respectively. Pathogenicity identification of the novel mutation showed that the p.E286K mutation is a disease-causing mutation. Our work enriches the human MAN2B1 gene mutation database. As far as we know, this research is thus far the first gene diagnosis case of a Chinese patient with α-mannosidosis.

The natural course and complications of alpha-mannosidosis--a retrospective and descriptive study

Most alpha-mannosidosis patients described have been children and information on the natural course of the disorder has been based on a very limited number of observations. In order to assess the disease presentation in detail and to study disease characteristics, a study was started in 1991 and has been ongoing for over 20 years. Patients with confirmed alpha-mannosidosis were recruited through The International Society for Mannosidosis and Related Diseases (ISMRD) where families affected with alpha-mannosidosis received a questionnaire on general clinical information to be filled out by the responsible physician. The questionnaire was returned by 125 patients (64%). Of these, 45 patients were 15 years old or older at the time of evaluation. The questionnaire allowed us to assess the following features: Facial dysmorphism, columnar disease, arthritis, myopathy, hearing impairment, mental impairment, psychosis, bone disease and motor function as well as general health. This study describes the progression of alpha-mannosidosis and may be helpful in determining the clinical characteristics for assessments of prognosis.

The effects of early and late bone marrow transplantation in siblings with alpha-mannosidosis. Is early haematopoietic cell transplantation the preferred treatment option?

This article documents both the neurological and physical outcomes of the first published set of siblings undergoing transplantation at differing ages for α-mannosidosis. The older brother, the index case, was diagnosed at the age of 3 years and underwent transplantation at 13 years for the treatment of increasing somatic problems and recurrent infections. The younger brother had undergone transplantation pre-symptomatically at 6 months of age. Their clinical, radiological and developmental outcomes are documented and compared with the previous published cases, with the case for early transplantation being weighted against other potential therapies.

Magnetic resonance spectroscopy of the occipital cortex and the cerebellar vermis distinguishes individual cats affected with alpha-mannosidosis from normal cats

A genetic deficiency of lysosomal alpha-mannosidase causes the lysosomal storage disease alpha-mannosidosis (AMD), in which oligosaccharide accumulation occurs in neurons and glia. The purpose of this study was to evaluate the role of magnetic resonance spectroscopy (MRS) in detecting the oligosaccharide accumulation in AMD. Five cats with AMD and eight age-matched normal cats underwent in vivo MRS studies with a single voxel short echo time (20 ms) STEAM spectroscopy sequence on a 4.7T magnet. Two voxels were studied in each cat, from the cerebellar vermis and the occipital cortex. Metabolites of brain samples from these regions were extracted with perchloric acid and analyzed by high resolution NMR spectroscopy. A significantly elevated unresolved resonance signal between 3.4 and 4. ppm was observed in the cerebellar vermis and occipital cortex of all AMD cats, which was absent in normal cats. This resonance was shown to be from carbohydrate moieties by high resolution NMR of tissue extracts. Resonances from the Glc-NAc group (1.8-2.2 ppm) along with anomeric proton signals (4.6-5.4 ppm) from undigested oligosaccharides were also observed in the extract spectra from AMD cats. This MRS spectral pattern may be a useful biomarker for AMD diagnosis as well as for assessing responses to therapy.

Apparent diffusion coefficient reveals gray and white matter disease, and T2 mapping detects white matter disease in the brain in feline alpha-mannosidosis

BACKGROUND AND PURPOSE

Methods to locate and identify brain pathology are critical for monitoring disease progression and for evaluating the efficacy of therapeutic intervention. The purpose of this study was to detect cell swelling, abnormal myelin, and astrogliosis in the feline model of the lysosomal storage disease alpha-mannosidosis (AMD) by using diffusion and T2 mapping.

MATERIALS AND METHODS

Average apparent diffusion coefficient (ADC(av)) and T2 were measured by imaging the brains of five 16-week-old cats with feline AMD on a 4.7T magnet. ADC(av) and T2 data from affected cats were compared with data from age-matched normal cats. Brains were collected from both affected and normal cats following imaging, and histology was compared with quantitative imaging data.

RESULTS

Gray matter from AMD cats demonstrated a 13%-15% decrease in ADC(av) compared with that in normal cats. White matter from AMD cats exhibited an 11%-16% decrease in ADC(av) and a 5%-12% increase in T2 values compared with those in normal control cats. Histologic evidence of neuronal and glial swelling, abnormal myelin, and astrogliosis was consistent with changes in ADC(av) and T2.

CONCLUSION

ADC(av) and T2 data can be used to quantify differences in the gray and white matter in the feline AMD brain and may serve as surrogate markers of neuronal swelling, abnormal myelin, and astrogliosis associated with this disease. These studies may be helpful in assessing the efficacy of experimental therapies for central nervous system disease associated with lysosomal storage diseases.

[Adult leukoencephalopathy caused by alpha-mannosidosis deficiency]

Adult leukoencephalopathy caused by alpha-mannosidosis deficiency (MIM248500) is a recessive inherited lysosomal storage disease associated with decreased activity of alpha-mannosidase. This enzyme degrades oligosaccharides and glycoproteins in neural and visceral tissues. There are two different disease phenotypes, type-I or severe infantile phenotype and type 2, which progresses more slowly and is compatible with survival into adulthood. We report the case of a 51-year-old man with gait disorders beginning at the age of 40 years associated with leukoencephalopathy due to alpha-mannosidosis deficiency.

Psychiatric symptoms in alpha-mannosidosis

Alpha-mannosidosis is characterized by mild to moderate intellectual disability (ID), moderate to severe neurosensory hearing loss, frequent infections, psychomotor disturbances and skeletal dysmorphism. For the first time, a panel of nine alpha-mannosidosis patients with psychiatric symptoms is presented. The clinical picture has several similarities: a physical or psychological stressor precedes a rapid development of a state of confusion, delusions, hallucinations, anxiety and often depression leading to a severe loss of function. This usually lasts 3-12 weeks, and is followed by a period of somnolence and asthenia. It may be more prevalent in females. In four of the described patients search for organic causes of the syndrome was performed, but revealed only negative findings. Because of the limited number of cases no firm conclusion about the benefit of various psychotropic drugs can be drawn from our observation. Psychiatric symptoms could affect as many as 25% of patients with alpha-mannosidosis. First onset is typically in late puberty to early adolescence. The episodes may be recurrent, and of limited duration although medication may be necessary to alleviate symptoms. Our observations indicate that alpha-mannosidosis is associated with an increased risk of psychiatric symptoms. These should not be dismissed as part of the ID but should give rise to the initiation of adequate diagnostic work-up, treatment and support.

Adult alpha-mannosidosis: clinical progression in the absence of demyelination

Alpha-mannosidosis is an inherited lysosomal storage disease. The authors report three siblings (ages 38 to 47 years) with the rare adult variant. All three had late-onset ataxia and retinal degeneration, adding to hearing loss, cognitive impairment, and dysotosis multiplex. One sibling also had psychosis. MRI revealed cerebellar atrophy and predominantly parieto-occipital white matter changes. MR spectroscopy showed no evidence for demyelination. It appears that the disabling course of adult alpha-mannosidosis is caused by lysosomal accumulation rather than demyelination.

Ungew�hnlicher Verlauf einer ?-Mannosidose mit Symptomen einer paranoid-halluzinatorischen Psychose

We report the case of a 27-year-old female with recurrent paranoid-hallucinatory episodes who was initially diagnosed as suffering from schizophrenic psychosis. After 10 years of treatment under this diagnosis, alpha-mannosidosis was identified to be the underlying cause of her psychiatric symptoms. alpha-Mannosidosis is a rare autosomal recessive lysosomal storage disorder associated with decreased activity of the enzyme mannosidase. In the present case, diagnosis was made late in the illness after failure of a response to antipsychotic treatment and with the patient additionally showing progressive cognitive decline. Only after extensive investigation was the diagnosis made by showing decreased alpha-mannosidase enzyme activity in serum and blood leukocytes. This case demonstrates that an unusual clinical course or striking symptom patterns, especially in association with somatic comorbidity, in psychotic patients should lead to diagnostic consideration of inherited metabolic disease.

Alpha-mannosidosis and mutational analysis in a Turkish patient

We present a case of alpha-mannosidosis with its mutational analysis. She was referred to our hospital with the provisional diagnosis of mucolipidosis. She was the first child of second-degree relative parents. She had a coarse face with flat and wide nasal bridge, hepatosplenomegaly, umbilical hernia, lumbar gibbus, motor and mental retardation and deafness. On peripheral blood smear, lymphocytes revealed vacuoles and neutrophils contained some granules resembling Reilly bodies seen in mucopolysaccharidosis (MPS). Based on these findings, the diagnosis of alpha-mannosidosis was suspected. Her urine oligosaccharide chromatography showed an abnormal pattern with a heavy trisaccharide band. Enzyme studies on white cells confirmed a deficiency of alpha-mannosidase activity, which was 2.6 micromol/g/hr. Her DNA analysis showed a S453Y mutation.

Histopathology, electrodiagnostic testing, and magnetic resonance imaging show significant peripheral and central nervous system myelin abnormalities in the cat model of alpha-mannosidosis

Alpha-mannosidosis is a disease caused by the deficient activity of alpha-mannosidase, a lysosomal hydrolase involved in the degradation of glycoproteins. The disease is characterized by the accumulation of mannose-rich oligosaccharides within lysosomes. The purpose of this study was to characterize the peripheral nervous system (PNS) and central nervous system (CNS) myelin abnormalities in cats from a breeding colony with a uniform mutation in the gene encoding alpha-mannosidase. Three affected cats and 3 normal cats from 2 litters were examined weekly from 4 to 18 wk of age. Progressively worsening neurological signs developed in affected cats that included tremors, loss of balance, and nystagmus. In the PNS, affected cats showed slow motor nerve conduction velocity and increased F-wave latency. Single nerve fiber teasing revealed significant demyelination/remyelination in affected cats. Mean G-ratios of nerves showed a significant increase in affected cats compared to normal cats. Magnetic resonance imaging of the CNS revealed diffuse white matter signal abnormalities throughout the brain of affected cats. Quantitative magnetization transfer imaging showed a 8%-16% decrease in the magnetization transfer ratio in brain white matter of affected cats compared to normal cats, consistent with myelin abnormalities. Histology confirmed myelin loss throughout the cerebrum and cerebellum. Thus, histology, electrodiagnostic testing, and magnetic resonance imaging identified significant myelination abnormalities in both the PNS and CNS that have not been described previously in alpha-mannosidosis.

Recent progress in lysosomal alpha-mannosidase and its deficiency

Lysosomal alpha-mannosidase (EC 3.2.1.24) is a major exoglycosidase in the glycoprotein degradation pathway. A deficiency of this enzyme causes the lysosomal storage disease, alpha-mannosidosis, which has been described in humans, cattle, domestic cats and guinea pigs. Recently, great progress has been made in studying the enzyme and its deficiency. This includes cloning of the gene encoding the enzyme, characterization of mutations related to the disease, establishment of valuable animal models, and encouraging results from bone marrow transplantation experiments.

Missense and nonsense mutations in the lysosomal alpha-mannosidase gene (MANB) in severe and mild forms of alpha-mannosidosis

alpha-Mannosidosis is an autosomal recessive lysosomal-storage disorder caused by a deficiency of lysosomal alpha-mannosidase activity. This disease shows a wide range of clinical phenotypes, from a severe, infantile form (type I), which is fatal at <3-8 years of age, to a less severe, late-onset form (type II), which ultimately may involve hearing loss, coarse face, mental retardation, and hepatosplenomegaly. To elucidate the molecular mechanism underlying this disease in both types of patients, we have used PCR, followed by either SSCP analysis or direct sequencing, to analyze the 24 exons and intron/exon boundaries of the alpha-mannosidase gene (MANB) from five patients. Two amino acid substitutions-H72L and R750W, in exons 2 and 18, respectively-and two nonsense mutations-Q639X and R760X, in exons 15 and 19, respectively-were identified in four type II patients. One amino acid substitution, P356R, was identified in exon 8 from a type I patient. This patient and three of the type II patients were homozygous for their mutations (H72L, P356R, R750W, and R760X) and one type II patient was heterozygous for the Q639X and R750W mutations. Transfection experiments of COS 7 cells, using the alpha-mannosidase cDNA containing one of the missense mutations-H72L, P356R, or R750W-revealed that each of these mutations dramatically reduces the enzymatic activity of alpha-mannosidase. These data demonstrate that widely heterogeneous missense or nonsense mutations of the MANB gene are the molecular basis underlying alpha-mannosidosis.

[Beta mannosidosis: a new case]

BACKGROUND

Only 11 cases of beta mannosidase deficiency have been reported until now. We report a new case.

CASE HISTORY

J was born at full term to consanguineous parents; her weight was 2,080 g and her height was 44 cm. During the first months of life she was hypotonic and had feeding difficulties. At the age of 7 months, she was admitted to an intensive care unit because of a serious inhalation. Standard blood analysis, chest X-ray, abdominal ultrasonography, electroencephalogram, cerebral nuclear magnetic resonance and electromyography were normal. Blood and urine amino acids and urine organic acids were also normal. The only detected abnormality was a marked deficiency of beta mannosidase in her serum and leukocytes. Later on, she suffered from recurring respiratory infections, and she had abnormalities of esophageal mobility, hypotoria of the lower esophageal sphincter, and at the age of 2 years, achalasia requiring surgery. To date, her motor development is retarded.

CONCLUSIONS

The main clinical manifestations of beta mannosidosis are various degrees of mental retardation, speech disorders and hearing loss. Our patient presented with abnormalities of swallowing and esophageal motility resulting in recurring respiratory infections, previously reported in some other cases.

Neurology of adult alpha-mannosidosis

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[Alpha-mannosidosis in two siblings]

A rare metabolic disease, alpha-mannosidosis, is described in two siblings. Psychomotoric deficiency, deafness, coarse face and radiological changes in the skeletal system indicated an inherited lysosomal storage disease.

Multiple suture synostosis, macrocephaly, and intracranial hypertension in a child with alpha-D-mannosidase deficiency. Case report

The authors present an unusual case in which increased intracranial pressure developed because of multiple-suture craniosynostosis and megaloencephaly in a child with a previously undiagnosed lysosomal storage disease, alpha-D-mannosidase deficiency. This 3-year-old boy presented with a history of frequent naps, headaches, florid papilledema, enlarged head (> 95th percentile), elevated opening pressure by lumbar puncture, a "beaten copper" appearance on skull radiographs, and no hydrocephalus. Multiple synostectomies were performed. Postoperatively, the child's headaches and papilledema resolved and his level of physical activity increased dramatically. The authors discuss the paradoxical presentation of prematurely fused sutures and macrocrania in light of this lysosomal storage disease and its subsequent management.

Alpha-mannosidosis: the first Turkish case

We describe a 10 month old boy with alpha-mannosidosis who presented with recurrent bronchopneumonia and diarrhea. Facial coarsening, deafness, hepatosplenomegaly, umbilical hernia, pectus carinatum and widespread Mongolian spots were distinguishing features. He also had mild skeletal deformities grouped together as 'dysostosis multiplex', and vacuolated lymphocytes on peripheral blood smear. These findings coupled with an abnormal urinary oligosaccharide pattern led to the suspicion of a lysosomal storage disease in the patient which proved to be alpha-mannosidosis. An exceptionally low level of alpha-mannosidase activity was subsequently found in serum and cultured skin fibroblasts. The patient's brother, who had died at the age of 10 months, had similar features. To the best of our knowledge, this is the first case reported from Turkey.

[Alpha-mannosidosis]

Alpha-mannosidosis is a rare autosomal recessively inherited lysosomal storage disorder. We describe three patients with alpha-mannosidosis who were born in Tromsø between 1983 and 1987, in order to increase awareness of the disease. It is characterized by a typical facial look, with a prominent forehead, hypertelorism, small nose, flat nasal bridge and hypoplastic teeth. The patients are mentally retarded, often have dysostosis multiplex, recurrent infections and typically severe loss of hearing and delayed speech development. The disease is slowly progressive in the first decade, but shows considerable clinical variability. In most cases, the lymphocytes are vacuolized, but diagnosis depends on measurement of alpha-mannosidase activity in the lymphocytes. Prenatal diagnosis is available, based on chorionic villi sampling in the 9th to 11th week of pregnancy. No causal therapy is known, but establishment of the diagnosis is important to avoid complications, recognize hearing loss and provide speech therapy and special education. The specific diagnosis is critical for genetic counselling and prenatal diagnosis. The authors therefore outline the diagnostic strategy.

Clinical and biochemical analysis of two families with type I and type II mannosidosis

We report on two unrelated patients with different presentations of mannosidosis. One patient was affected in early childhood with a severe phenotype characteristic of type I mannosidosis. The other was diagnosed with type II mannosidosis only after the onset of progressive neurologic deterioration in late adulthood. Both were detected by non-invasive urinary screening of oligosaccharides. Lymphoblasts transformed from both patients' blood cells had markedly reduced lysosomal alpha-mannosidase activity. Kinetic analyses showed that alpha-mannosidase from the type I patient had a 400-fold reduction in affinity while that from the type II patient was reduced 40-fold. Lymphoblasts from all 4 parents had reduced alpha-mannosidase activity, but there were overlapping activities among these type I and type II obligate heterozygotes. We conclude that screening urinary oligosaccharides will detect mannosidosis over a wide range of phenotypes, that lymphoblasts transformed from affected heterozygotes have decreased enzymatic activity, and that the severity of clinical expression is related to the degree of enzyme impairment.

Storage disorders presenting like mucopolysaccharidosis

The term dysostosis multiplex is specifically applied to the group of radiological features collectively found in a number of specific metabolic disorders including the mucopolysaccharidoses, mucolipidosis, mannosidosis, fucosidosis and several other rarer conditions. We report eight cases of mannosidosis, fucosidosis and mucolipidosis with special emphasis on the differentiation from the more common mucopolysaccharidoses.

Human chorionic beta-mannosidase: comparison with beta-mannosidase from human cultured fibroblasts

The conditions for assay of beta-mannosidase activity in human chorionic villi (CV) were studied using the fluorogenic substrate 4-methylumbelliferyl-beta-D-mannopyranoside. A comparison of the biochemical properties of the CV beta-mannosidase with those of the enzyme from human cultured fibroblasts showed their similarity. Like the enzyme from skin fibroblasts, the CV beta-mannosidase had rather high activity. Both enzymes had virtually the same pH optimum (4.2-4.7) and Km value. The data presented suggest that chorion biopsy specimens can be used for prenatal determination of beta-mannosidase activity at an early stage of development.

First reported case of alpha-mannosidosis in the RSA

The first known case of alpha-mannosidosis in the RSA is reported. Presentation was classic, viz. delayed speech, kyphoscoliosis and hearing loss at the age of 4 years. Among the generally rare inherited lysosomal storage diseases, alpha-mannosidosis is regarded in Europe and the USA as one of the more common disorders. It is suggested that the apparent underdiagnosis in South Africa may stem from lack of clinical recognition of a condition, which is relatively simple to diagnose biochemically. The clinical and radiological features of the child are described in the hope that clinicians will develop an awareness of the disorder, and include it in the differential diagnosis of deaf children who may also have mild skeletal abnormalities. Antenatal diagnosis of this untreatable condition is possible, so the birth of further affected children in a family could be prevented.

[A case of mannosidosis type II]

A case of L-mannosidosis, a recessively inherited thesaurosis, is reported. Since birth the patient had evidence of immunodeficiency. The neurological manifestations developed during adolescence with slurred and slow speech with scanning, muscle flaccidity, sings of Trömner and Jacobson, intentional tremor, equilibrium disturbances. After many laboratory investigations the tests for inherited metabolic disorders made the correct diagnosis possible.

First-trimester diagnosis of an unusual case of alpha-mannosidosis

Chorionic villi obtained in the first trimester from a pregnancy at risk for alpha-mannosidosis were shown to have reduced alpha-mannosidase (EC 3.2.1.24) activity. The pregnancy was terminated and subsequent enzyme studies of the fetal tissues were consistent with the diagnosis of alpha-mannosidosis. Like the enzyme in the child's fibroblast, alpha-mannosidase of the chorionic villi from a pregnancy at risk for alpha-mannosidosis was activated by high substrate concentration and by Zn2+, and displayed a Km value two-fold higher than normal. Our results confirm that chorionic villi can be used for early prenatal diagnosis of alpha-mannosidosis.

MR findings in mannosidosis

MR findings are reported in three patients presenting mannosidosis. Among a family of 8 children, 4 presented typical clinical and biological abnormalities related to mannosidosis. Brain MR examinations including sagittal T1 and axial T2 sections were obtained in three patients of this family (one 25-year-old male, one 34-year-old female, and one 35-year-old female). MR scans demonstrate seven types of modifications: (1) brachycephaly, (2) thick calvaria, (3) verticalization of the chiasmatic sulcus, (4) poor pneumatization of the sphenoid body, (5) partial empty sella turcica (6) cerebellar atrophy, and (7) white matter signal modifications. High signal abnormalities involving the parieto-occipital white matter are identified on axial T2-weighted scans in the three patients and are probably related to demyelination and associated gliosis as described previously by several authors on specimens.

Lectin histochemistry of the central nervous system in a case of feline alpha-mannosidosis

The diagnosis of feline alpha-mannosidosis is made by demonstrating deficient activity of the enzyme alpha-mannosidase or an elevation of its undergraded substrate in body fluids or tissue. In this study the storage of specific sugar residues in the brain and spinal cord in a case of feline alpha-mannosidosis was examined by means of nine different biotinylated lectins and the avidin-biotin-peroxidase method on formalin-fixed, paraffin-embedded tissue sections. The lectin staining pattern strongly correlated with the known biochemical findings of the stored oligosaccharides in feline alpha-mannosidosis and was different from the lectin reactivity of normal cat tissues. This confirms that lectin histochemistry is a simple, relatively inexpensive and reliable method for diagnosing alpha-mannosidosis in cats.

[Prenatal diagnosis of mannosidosis using chorion villi]

The prenatal diagnosis of mannosidosis was carried out in one at-risk fetus by the analysis of chorionic villi obtained after 9 weeks of pregnancy. The diagnosis was based on the absence of acid alpha-mannosidase activity as determined by specific enzyme assay. The activity of two other lysosomal hydrolases (beta-galactosidase and beta-hexosaminidase) in chorion biopsy specimen was similar to the control values. The enzymatic diagnosis was confirmed after studies of fetal tissue.

Caprine beta-mannosidosis: phenotypic features

The clinical features of caprine beta-mannosidosis were evaluated in 10 newborn goats, one stillborn goat and one goat fetus. The phenotypic abnormalities observed in all 10 live affected animals included an inability to rise from a recumbent position, moderate to marked intention tremor, eye movements resembling pendular nystagmus, clinical deafness, bilateral Horner's syndrome, carpal contractures, pastern joint hyperextension, thickened skin and to a varying degree, a dome-shaped skull. Subjective evaluation suggested that most animals had a decreased muscle mass. Together, these characteristics represent a common phenotype which is expressed at birth in caprine beta-mannosidosis.

Oligosaccharides from placenta: early diagnosis of feline mannosidosis

High-pressure liquid chromatography analysis of oligosaccharides from placentas allowed the diagnosis of alpha-mannosidosis in three litters of kittens. The chromatography also afforded a detailed comparison of the oligosaccharide pattern and levels in placenta, liver, brain, urine and ocular fluid of the affected animals. In all cases, two series of compounds were observed, with one or two residues of N-acetylglucosamine at the reducing terminus, respectively, and between two and nine mannose residues. This pattern is unlike that of human mannosidosis, and resembles that of ruminants, except that the major oligosaccharide contains three mannose residues instead of two.

Identification of glycoprotein storage diseases by lectins: a new diagnostic method

The specific diagnosis of glycoprotein storage diseases is made by demonstrating a deficiency in enzyme activity or an elevation of undegraded oligosaccharides in cells or body fluids. Prospective sampling and expensive specialized biochemistry, which is also time consuming, are required for such studies. We used lectin reagents on paraffin-embedded tissue sections to identify the specific sugars in undegraded stored substances. We studied 22 cases of glycoprotein storage diseases and differentiated histochemically between alpha- and beta-mannosidosis, fucosidosis, and sialisidosis. Cells affected with alpha-mannosidosis stained with Concanavalia ensiformis (Con A), Triticum vulgaris (WGA), and succinyl-WGA (S-WGA), while beta-mannosidosis cells did not stain with any of the lectins used. In fucosidosis the affected cells stained with Ulex europeus-I (UEA-I), while sialisidosis-affected cells stained with WGA, and in three cases with Arachis hypogea (PNA). This study indicates that lectin histochemistry provides a reliable specific diagnostic pattern for some glycoprotein storage diseases using a simple and inexpensive method.