Mild phenotypic expression of alpha-N-acetylgalactosaminidase deficiency in two adult siblings

Hearing loss in inherited metabolic disorders: A systematic review

Inherited metabolic disorders (IMDs) have been observed in individuals with hearing loss (HL), but IMDs are rarely the cause of syndromic HL. With early diagnosis, management of HL is more effective and cortical reorganization is possible with hearing aids or cochlear implants. This review describes relationships between IMDs and HL in terms of incidence, etiology of HL, pathophysiology, and treatment. Forty types of IMDs are described in the literature, mainly in case reports. Management and prognosis are noted where existing. We also describe IMDs with HL given age of occurrence of HL. Reviewing the main IMDs that are associated with HL may provide an additional clinical tool with which to better diagnose syndromic HL.

A New Case of Schindler Disease

Lysosomal storage disorders (LSDs) are a group of genetic disorders caused by mutations in genes encoding enzymes involved in lysosomal function. Schindler disease is an autosomal recessive, inherited LSD caused by defective or non-existent activity of the enzyme α-N-acetylgalactosaminidase (α-NAGA). To date, three main phenotypes of Schindler disease have been described. We report the case of a 68-year-old man presenting with axonal and demyelinating polyneuropathy, sensorineural hearing loss, chronic lymphoedema, angiokeratoma corporis diffusum and bilateral carpal tunnel syndrome. Genetic testing (PCR) for α-galactosidase revealed the c.577G>T (p.Glu193*) mutation in the NAGA gene, confirming Schindler disease, which is clinically compatible with Kanzaki disease and Schindler disease type II.

Inhibition of Mitochondrial Complex I Impairs Release of α-Galactosidase by Jurkat Cells

Fabry disease (FD) is caused by mutations in the GLA gene that encodes lysosomal α-galactosidase-A (α-gal-A). A number of pathogenic mechanisms have been proposed and these include loss of mitochondrial respiratory chain activity. For FD, gene therapy is beginning to be applied as a treatment. In view of the loss of mitochondrial function reported in FD, we have considered here the impact of loss of mitochondrial respiratory chain activity on the ability of a GLA lentiviral vector to increase cellular α-gal-A activity and participate in cross correction. Jurkat cells were used in this study and were exposed to increasing viral copies. Intracellular and extracellular enzyme activities were then determined; this in the presence or absence of the mitochondrial complex I inhibitor, rotenone. The ability of cells to take up released enzyme was also evaluated. Increasing transgene copies was associated with increasing intracellular α-gal-A activity but this was associated with an increase in Km. Release of enzyme and cellular uptake was also demonstrated. However, in the presence of rotenone, enzyme release was inhibited by 37%. Excessive enzyme generation may result in a protein with inferior kinetic properties and a background of compromised mitochondrial function may impair the cross correction process.

Lysosomal storage diseases

Lysosomes are cytoplasmic organelles that contain a variety of different hydrolases. A genetic deficiency in the enzymatic activity of one of these hydrolases will lead to the accumulation of the material meant for lysosomal degradation. Examples include glycogen in the case of Pompe disease, glycosaminoglycans in the case of the mucopolysaccharidoses, glycoproteins in the cases of the oligosaccharidoses, and sphingolipids in the cases of Niemann-Pick disease types A and B, Gaucher disease, Tay-Sachs disease, Krabbe disease, and metachromatic leukodystrophy. Sometimes, the lysosomal storage can be caused not by the enzymatic deficiency of one of the hydrolases, but by the deficiency of an activator protein, as occurs in the AB variant of GM2 gangliosidosis. Still other times, the accumulated lysosomal material results from failed egress of a small molecule as a consequence of a deficient transporter, as in cystinosis or Salla disease. In the last couple of decades, enzyme replacement therapy has become available for a number of lysosomal storage diseases. Examples include imiglucerase, taliglucerase and velaglucerase for Gaucher disease, laronidase for Hurler disease, idursulfase for Hunter disease, elosulfase for Morquio disease, galsulfase for Maroteaux-Lamy disease, alglucosidase alfa for Pompe disease, and agalsidase alfa and beta for Fabry disease. In addition, substrate reduction therapy has been approved for certain disorders, such as eliglustat for Gaucher disease. The advent of treatment options for some of these disorders has led to newborn screening pilot studies, and ultimately to the addition of Pompe disease and Hurler disease to the Recommended Uniform Screening Panel (RUSP) in 2015 and 2016, respectively.

Fabry Disease: A Disorder of Childhood Onset

BACKGROUND

Fabry disease, an X-linked disorder of glycosphingolipids, markedly increases the risk of systemic vasculopathy, ischemic stroke, small-fiber peripheral neuropathy, cardiac dysfunction, and chronic kidney disease.

METHODS

We performed an extensive PubMed search on the topic of Fabry disease and drew from our cumulative 43 years of experience.

RESULTS

Most of these complications are nonspecific in nature and clinically indistinguishable from similar abnormalities that occur in the context of more common disorders in the general population. This disease is caused by variants of the GLA gene, and its incidence may have been underestimated. However, one must also guard against overdiagnosis of Fabry disease and unjustified enzyme replacement therapy, because some of the gene variants are benign. Specific therapy for Fabry disease has been developed in the last few years, but its clinical effect has been modest. Novel therapeutic agents are being developed. Standard "nonspecific" medical and surgical therapy is necessary and effective in slowing deterioration or compensating for organ failure in patients with Fabry disease.

CONCLUSIONS

Fabry disease is a treatable and modifiable genetic risk factor for a myriad of clinical organ complications. Fabry disease may be frequently overlooked but on occasion overdiagnosed.

The 1.9 a structure of human alpha-N-acetylgalactosaminidase: The molecular basis of Schindler and Kanzaki diseases

alpha-N-acetylgalactosaminidase (alpha-NAGAL; E.C. 3.2.1.49) is a lysosomal exoglycosidase that cleaves terminal alpha-N-acetylgalactosamine residues from glycopeptides and glycolipids. In humans, a deficiency of alpha-NAGAL activity results in the lysosomal storage disorders Schindler disease and Kanzaki disease. To better understand the molecular defects in the diseases, we determined the crystal structure of human alpha-NAGAL after expressing wild-type and glycosylation-deficient glycoproteins in recombinant insect cell expression systems. We measured the enzymatic parameters of our purified wild-type and mutant enzymes, establishing their enzymatic equivalence. To investigate the binding specificity and catalytic mechanism of the human alpha-NAGAL enzyme, we determined three crystallographic complexes with different catalytic products bound in the active site of the enzyme. To better understand how individual defects in the alpha-NAGAL glycoprotein lead to Schindler disease, we analyzed the effect of disease-causing mutations on the three-dimensional structure.

Fabry disease

Fabry disease, an X-linked disorder of glycosphingolipids that is caused by the deficiency of alpha-galactosidase A, is associated with dysfunction of many cell types and includes a systemic vasculopathy. As a result, patients have a markedly increased risk of developing small-fiber peripheral neuropathy, stroke, myriad cardiac manifestations and chronic renal disease. Virtually all complications of Fabry disease are non-specific in nature and clinically indistinguishable from similar abnormalities that occur in the context of more common disorders in the general population. Although Fabry disease was originally thought to be very rare, recent studies have found a much higher incidence of mutations of the GLA gene, suggesting that this disorder is under-diagnosed. Although the etiology of Fabry disease has been known for many years, the mechanism by which the accumulating alpha-D-galactosyl moieties cause this multi-organ disorder has only recently been studied and is yet to be completely elucidated. Specific therapy for Fabry disease has been developed in the last few years but its role in the management of the disorder is still being investigated. Fortunately, standard 'non-specific' medical and surgical therapy is effective in slowing deterioration or compensating for organ failure in patients with Fabry disease. All these aspects are discussed in detail in the present review.

Structural and immunocytochemical studies on alpha-N-acetylgalactosaminidase deficiency (Schindler/Kanzaki disease)

Alpha-N-acetylgalactosaminidase (alpha-NAGA) deficiency (Schindler/Kanzaki disease) is a clinically and pathologically heterogeneous genetic disease with a wide spectrum including an early onset neuroaxonal dystrophy (Schindler disease) and late onset angiokeratoma corporis diffusum (Kanzaki disease). In alpha-NAGA deficiency, there are discrepancies between the genotype and phenotype, and also between urinary excretion products (sialyl glycoconjugates) and a theoretical accumulated material (Tn-antigen; Gal NAcalpha1-O-Ser/Thr) resulting from a defect in alpha-NAGA. As for the former issue, previously reported genetic, biochemical and pathological data raise the question whether or not E325K mutation found in Schindler disease patients really leads to the severe phenotype of alpha-NAGA deficiency. The latter issue leads to the question of whether alpha-NAGA deficiency is associated with the basic pathogenesis of this disease. To clarify the pathogenesis of this disease, we performed structural and immunocytochemical studies. The structure of human alpha-NAGA deduced on homology modeling is composed of two domains, domain I, including the active site, and domain II. R329W/Q, identified in patients with Kanzaki disease have been deduced to cause drastic changes at the interface between domains I and II. The structural change caused by E325K found in patients with Schindler disease is localized on the N-terminal side of the tenth beta-strand in domain II and is smaller than those caused by R329W/Q. Immunocytochemical analysis revealed that the main lysosomal accumulated material in cultured fibroblasts from patients with Kanzaki disease is Tn-antigen. These data suggest that a prototype of alpha-NAGA deficiency in Kanzaki disease and factors other than the defect of alpha-NAGA may contribute to severe neurological disorders, and Kanzaki disease is thought to be caused by a single enzyme deficiency.

Angiokeratoma corporis diffusum in a Spanish patient with aspartylglucosaminuria

Angiokeratoma corporis diffusum (ACD), initially considered to be synonymous with Fabry's disease, represents a well-known cutaneous marker of some other lysosomal enzyme disorders. Aspartylglucosaminuria (AGU) is a rare hereditary disorder mostly affecting the Finnish population, with only a few sporadic patients of non-Finnish origin. To date, only three patients with AGU have been reported with cutaneous lesions of ACD. A 19-year-old Spanish woman presented with a 10-year history of progressive ACD affecting the limbs, buttocks and trunk. After the age of 6 years she had developed progressive mental deterioration, coarse facies and macroglossia with a scrotal appearance. Peripheral blood smears showed many vacuolated lymphocytes. Enzyme analysis in cultured fibroblasts revealed a decreased activity of aspartylglucosaminidase. By the age of 31 years the patient had developed a bipolar psychosis, polycystic ovarian disease and severe impairment of cognitive skills. This is the first case of AGU detected in a Spanish patient presenting with cutaneous lesions of ACD. To our knowledge, macroglossia with a scrotal appearance and polycystic ovarian disease have not been reported in previous cases of AGU.

Defects in degradation of blood group A and B glycosphingolipids in Schindler and Fabry diseases

Skin fibroblast cultures from patients with inherited lysosomal enzymopathies, alpha-N-acetylgalactosaminidase (alpha-NAGA) and alpha-galactosidase A deficiencies (Schindler and Fabry disease, respectively), and from normal controls were used to study in situ degradation of blood group A and B glycosphingolipids. Glycosphingolipids A-6-2 (GalNAc (alpha 1-->3)[Fuc alpha 1-->2]Gal(beta1-->4)GlcNAc(beta 1-->3)Gal(beta 1--> 4)Glc (beta 1-->1')Cer, IV(2)-alpha-fucosyl-IV(3)-alpha-N-acetylgalactosaminylneolactotetraosylceramide), B-6-2 (Gal(alpha 1-->3)[Fuc alpha 1--> 2] Gal (beta 1-->4)GlcNAc(beta 1-->3)Gal(beta 1-->4)Glc(beta 1-->1')Cer, IV(2)- alpha-fucosyl-IV(3)-alpha-galactosylneolactotetraosylceramide), and globoside (GalNAc(beta 1-->3)Gal(alpha 1-->4)Gal(beta 1-->4)Glc(beta 1-->1') Cer, globotetraosylceramide) were tritium labeled in their ceramide moiety and used as natural substrates. The degradation rate of glycolipid A-6-2 was very low in fibroblasts of all the alpha-NAGA-deficient patients (less than 7% of controls), despite very heterogeneous clinical pictures, ruling out different residual enzyme activities as an explanation for the clinical heterogeneity. Strongly elevated urinary excretion of blood group A glycolipids was detected in one patient with blood group A, secretor status (five times higher than upper limit of controls), in support of the notion that blood group A-active glycolipids may contribute as storage compounds in blood group A patients. When glycolipid B-6-2 was fed to alpha-galactosidase A-deficient cells, the degradation rate was surprisingly high (50% of controls), while that of globotriaosylceramide was reduced to less than 15% of control average, presumably reflecting differences in the lysosomal enzymology of polar glycolipids versus less-polar ones. Relatively high-degree degradation of substrates with alpha-D-Galactosyl moieties hints at a possible contribution of other enzymes.

A new case of alpha-N-acetylgalactosaminidase deficiency with angiokeratoma corporis diffusum, with Ménière's syndrome and without mental retardation

alpha-N-acetylgalactosaminidase (alpha-NAGA) deficiency is a rare hereditary lysosomal storage disease, and only three alpha-NAGA-deficient patients with angiokeratoma corporis diffusum (Kanzaki) have been described. We report a further case in a 47-year-old Japanese woman, the product of a consanguineous marriage. The remarkable findings in this patient were her normal intelligence, Ménière's syndrome, disturbance of peripheral sensory nerves, hearing loss and cardiac hypertrophy. alpha-NAGA enzyme activity in her plasma was 0.77% of the normal value. Other enzyme activities, such as alpha-galactosidase, beta-galactosidase, alpha-L-fucosidase, beta-mannosidase and aspartylglucosaminidase, were within normal limits. A large quantity of amino acid O-glycans was detected in her urine. Gene analysis revealed a novel point mutation (G-->A transition) at nucleotide 11018 (986 in the cDNA) resulting in an Arg-329-Gln substitution. Kanzaki disease has the same enzyme defect as Schindler disease, but the manifestations are quite different.

Human alpha-N-acetylgalactosaminidase (alpha-NAGA) deficiency: no association with neuroaxonal dystrophy?

Two new individuals with alpha-NAGA deficiency are presented. The index patient, 3 years old, has congenital cataract, slight motor retardation and secondary demyelinisation. Screening of his sibs revealed an alpha-NAGA deficiency in his 7-year-old healthy brother who had no clinical or neurological symptoms. Both sibs are homozygous for the E325K mutation, the same genotype that was found in the most severe form of alpha-NAGA deficiency presenting as infantile neuroaxonal dystrophy. Thus, at the age of 7 years the same genotype of alpha-NAGA may present as a 'non-disease' (present healthy case) and can be associated with the vegetative state (the first two patients described with alpha-NAGA deficiency). The clinical heterogeneity among the 11 known individuals with alpha-NAGA deficiency is extreme, with a 'non-disease' (two cases) and infantile neuroaxonal dystrophy (two cases) at the opposite sides of the clinical spectrum. The broad spectrum is completed by a very heterogeneous group of patients with various degrees of epilepsy/behavioural difficulties/psychomotor retardation (four patients) and a mild phenotype in adults without overt neurological manifestations who have angiokeratoma and clear vacuolisation in various cell types (three cases). These observations are difficult to reconcile with a straightforward genotype-phenotype correlation and suggest that factors or genes other than alpha-NAGA contribute to the clinical heterogeneity of the 11 patients with alpha-NAGA deficiency.

Glycoprotein lysosomal storage disorders: alpha- and beta-mannosidosis, fucosidosis and alpha-N-acetylgalactosaminidase deficiency

Glycoproteinoses belong to the lysosomal storage disorders group. The common feature of these diseases is the deficiency of a lysosomal protein that is part of glycan catabolism. Most of the lysosomal enzymes involved in the hydrolysis of glycoprotein carbohydrate chains are exo-glycosidases, which stepwise remove terminal monosaccharides. Thus, the deficiency of a single enzyme causes the blockage of the entire pathway and induces a storage of incompletely degraded substances inside the lysosome. Different mutations may be observed in a single disease and in all cases account for the nonexpression of lysosomal glycosidase activity. Different clinical phenotypes generally characterize a specific disorder, which rather must be described as a continuum in severity, suggesting that other biochemical or environmental factors influence the course of the disease. This review provides details on clinical features, genotype-phenotype correlations, enzymology and biochemical storage of four human glycoprotein lysosomal storage disorders, respectively alpha- and beta-mannosidosis, fucosidosis and alpha-N-acetylgalactosaminidase deficiency. Moreover, several animal disorders of glycoprotein metabolism have been found and constitute valuable models for the understanding of their human counterparts.

Cerebral glucose metabolism in type I alpha-N-acetylgalactosaminidase deficiency: an infantile neuroaxonal dystrophy

Cerebral glucose metabolism was investigated in a 4.8-year-old boy with alpha-N-acetylgalactosaminidase deficiency using 2-[18F]fluoro-2-deoxy-D-glucose and positron emission tomography (PET). In comparison to normal values for age, the overall cerebral glucose metabolism was reduced and the regional cerebral glucose metabolism was decreased in proportion to the degree of atrophy. In the supratentorial cortical regions, the hypometabolism was asymmetric. However, the level of regional cerebral glucose metabolism in all cortical regions excluded a persistent vegetative state. In the lentiform nucleus and the head of the caudate, comparatively increased regional cerebral glucose metabolism was documented, similar to findings in neurodegenerative disorders with active epilepsy. In contrast, the infratentorial structures (cerebellar hemispheres, brain stem, mesencephalon, and hypothalamus), which are predominantly affected by the atrophic process, showed distinct and symmetric hypometabolism. Thus, the 2-[18F]-fluoro-2-deoxy-D-glucose PET scans provided additional insight into and correlation of the functional and structural disturbances in type I alpha-N-acetylgalactosaminidase deficiency, in addition to documenting the hypometabolism due to brain atrophy.

Molecular cloning, structural organization, sequence, chromosomal assignment, and expression of the mouse alpha-N-acetylgalactosaminidase gene

Alpha-N-acetylgalactosaminidase (2-acetamido-2-deoxy-alpha-d-galactoside acetamidodeoxy-galactohydrolase, NAGA; EC 3.2.1.49) deficiency is a recently recognized autosomal recessive lysosomal disease. As a prerequisite for the generation of an animal model, the mouse NAGA gene was cloned and characterized. The NAGA gene was assigned to mouse chromosome 15 band E3, syntenic to the region encompassing the human gene, and NAGA-deficient mutant human cells transfected with the cosmid clone containing the mouse NAGA gene expressed NAGA activity. Comparison of the mouse NAGA nucleotide sequence with the human NAGA sequence predicted that the mouse NAGA gene contains an open reading frame of 1245bp, comprising nine coding exons and spanning a genomic region of 8258bp, and a 3' untranslated region of 0.5kb. The 5' untranslated region was determined in primer extension studies to be 235bp in length. Nucleotide identity between the human and mouse NAGA exons ranged from 67.4 to 89.5%, with better matches for exons 1-7 than for 8 and 9. The overall amino acid identity between the mouse and human deduced NAGA polypeptides was 82.0%, between those of mouse and chicken 72.9%. Homology was found to only one other mouse gene, i.e. the alpha-galactosidase A (GALA; EC 3.2.1. 22) gene. The amino acid identity ranged from 51.6 to 62.1% in the polypeptide regions corresponding to NAGA exons 2-7 and GALA exons 1-6, but little, if any, in the remainder. These analyses gave emphasis to the strong conservation of the NAGA gene and its origin from an ancestor common with the GALA gene, with NAGA exons 8 and 9 and GALA exon 7 being the most divergent regions in the evolution of the two genes.

Cutaneous vascular anomalies. Part I. Hamartomas, malformations, and dilation of preexisting vessels

Classification of cutaneous vascular anomalies is difficult because conceptual confusion persists between vascular neoplasms and malformations. However, hemangiomas of the infancy fulfill criteria both for hyperplasia and neoplasm because they result from proliferation of endothelial cells, but often undergo complete regression. Despite these pitfalls we have classified cutaneous vascular anomalies into the following categories: hamartomas, malformations, dilatations of preexisting vessels, hyperplasias, benign neoplasms, and malignant neoplasms. In this first part of our clinicopathologic review of vascular anomalies, hamartomas, malformations, and dilatation of preexisting vessels are covered. Hamartomas include several combined vascular and melanocytic proliferations grouped as phakomatosis pigmentovascularis and the so-called eccrine angiomatous hamartoma that consists of proliferations of both eccrine glands and blood vessels. Vascular malformations result from anomalies of embryologic development, and in some of them the abnormalities of the involved vessels are more functional than anatomic, as is the case of nevus anemicus. In contrast, other cutaneous vascular malformations show striking morphologic abnormalities of the vascular structures. These anatomic vascular malformations are subdivided into the following groups: capillary, venous, arterial, lymphatic, and combined anomalies. Spider angioma, capillary aneurysm-venous lake, and telangiectases are not vascular proliferations at all, but dilations of preexisting vessels. In our opinion, most of the lesions described with the generic term of "angiokeratoma" are not authentic vascular neoplasms, but hyperkeratotic malformations of capillaries and venules or acquired telangiectases of preexisting blood vessels of the papillary dermis. Therefore the first group of these "angiokeratomas" are included in the vascular malformations section, and the second group are covered in the section of dilation of preexisting vessels. Lymphangiectases are considered the lymphatic counterpart of angiokeratomas because they result from ectasia of preexisting lymphatic vessels of the papillary dermis.

Human alpha-N-acetylgalactosaminidase (alpha-NAGA) deficiency: new mutations and the paradox between genotype and phenotype

Up to now eight patients with alpha-NAGA deficiency have been described. This includes the newly identified patient reported here who died unexpectedly aged 1 1/2 years of hypoxia during convulsions; necropsy was not performed. Three patients have been genotyped previously and here we report the mutations in the other five patients, including two new mutations (S160C and E193X). The newly identified patient is consanguineous with the first patients reported with alpha-NAGA deficiency and neuroaxonal dystrophy and they all had the alpha-NAGA genotype E325K/E325K. Clinical heterogeneity among patients with alpha-NAGA deficiency is extreme. Two affected sibs, homozygotes for E325K, are severely affected and have the signs and symptoms of infantile neuroaxonal dystrophy, but prominent vacuolisation is lacking. The mildly affected patients (two families, three patients) at the opposite end of the clinical spectrum have clear vacuolisation and angiokeratoma but no overt neurological manifestations. Two of them are homozygous for the stop mutation E193X, leading to complete loss of alpha-NAGA protein. These observations are difficult to reconcile with a simple genotype-phenotype correlation and we suggest that factors or genes other than alpha-NAGA contribute to the clinical heterogeneity of the eight patients with alpha-NAGA deficiency. At the metabolic level, the patients with alpha-NAGA deficiency are similar. The major abnormal urinary oligosaccharides are sialylglycopeptides of the O linked type. Our enzymatic studies indicated that these compounds are not the primary lysosomal storage products.