The nosology of the mucopolysaccharidoses

Evaluation of Patients Referred to Children's Medical Center Laboratory for Diagnosis of Mucopolysaccharidoses: Eight Years' Experience from Iran

Mucopolysaccharidoses (MPSs) are rare lysosomal storage diseases, resulting from deficiencies of enzymes responsible for Glycosaminoglycans (GAGs) degradation. This leads to accumulation of GAGs in tissues and their excretion in urine, with a wide variety of manifestations. Early diagnosis of MPSs is strictly recommended due to available therapy that can slow down disease progression during the early ages. This study aimed to evaluate patients with suspected MPS referred to Children's Medical Center laboratory over eight years. We also evaluated the usefulness of urine GAG as a screening test for identification of such patients. A total of 1414 patients (40% female, 60% male, with mean age 3.1 ± 4.1years) have participated in this study. The urinary GAG analysis (uGAG) was performed by 1, 9-dimethyl-methylene blue (DMMB) and Berry spot test (BST). All patients with positive and mild positive results or with disease-related symptoms were evaluated in terms of definitive diagnosis, received treatments, morbidity, and mortality rate. In 407 (36.5%) patients uGAG were positive or mild positive, of which 26.3% suffered from one of the types of MPSs, 28.5% suffered from other diseases, 32.9% were undiagnosed, 12.3% were apparently healthy, and 19 died. The negative predictive value of uGAG test in our study was 100%. About 21% of MPSs patients received enzyme replacement therapy, while four patients underwent stem cell transplants. The rest received supportive care. We concluded that a combination of DMMB and BST methods has acceptable sensitivity for screening suspicious MPS patients.

Current state of the art in treatment of Mendelian disease: Skeletal dysplasias

The current state of the art in treatment of Mendelian disease, specifically skeletal dysplasias, benefits tremendously from Dr. Victor McKusick's early delineation and standardization of the nomenclature surrounding these conditions. Through close observation and careful description of each dysplasia to flesh out the nosologic backbone of the genetic skeletal disorders, individuals with the same diagnosis were identified and grouped together for genetic interrogation. These efforts have resulted in the identification of the genetic etiology of nearly all recognized skeletal disorders. This, in turn, is leading to disease-specific treatment for many of the skeletal dysplasias in this new era of precision medicine. Furthermore, Dr. McKusick's natural history descriptions of many genetic skeletal disorders helped to establish the baseline disease state against which the effect of new treatment is compared.

[Mucopolysaccharidosis: clinical features, diagnosis and management]

The mucopolysaccharidoses (MPS) are a group of rare (orphan) diseases, characterised by a deficiency of enzymes involved in the metabolism of glycosaminoglycans (GAGs) at lysosomal level. When there is a deficiency of a particular enzyme there is an accumulation of GAGs in the cells resulting in progressive cellular damage, which can affect multiple organ systems and lead to organ failure. Diagnosis is based on knowledge of the clinical manifestations, performing biochemical analyses to identify the type of GAG that is accumulating, and confirm the type of disorder with the corresponding enzymatic determination. Their identification is essential to initiate early treatment, taking into account that multidisciplinary management and enzyme replacement therapy is available for MPS I (Hurler syndrome), MPS II (Hunter syndrome), MPS IV (Morquio syndrome), and MPS VI (Maroteaux-Lamy syndrome. In this review, an analysis is made of each of these syndromes, as well as their diagnosis and treatment.

Mucopolysacccharidoses: From understanding to treatment, a century of discoveries

After the first description of a patient recognized as a MPS case was made in 1917, several similar cases were described and identified. Observations reported in the middle of the twentieth century concerning the presence of acid mucopolysaccharides (later called glycosaminoglycans, or GAGs) in tissues and especially in urine of patients were instrumental in providing an identity for these diseases, which became referred as "mucopolysaccharidoses" (MPS). In the late 1960's it was demonstrated that MPS were caused by defects in the breakdown of GAGs, and the specific enzyme deficiencies for the 11 types and subtypes of MPS were identified thereafter. Genes involved in the MPS were subsequently identified, and a large number of disease-causing mutations were identified in each one. Although individually rare, MPS are relatively frequent as a group, with an overall incidence estimated as 1:22,000. The increased excretion of urinary GAGs observed in the vast majority of MPS patients provides a simple screening method, the diagnosis usually being confirmed by the identification of the specific enzyme deficiency. Molecular analysis also plays a role, being helpful for phenotype prediction, prenatal diagnosis and especially for the identification of carriers. As the diseases are rare and diagnosis requires sophisticated methods, the establishment of reference laboratories for MPS identification is recommended. The successful experience of the MPS Brazil Network in providing access to information and diagnosis may be considered as an option for developing countries. The development of therapeutic strategies for MPS, including bone marrow/hematopoietic stem cell transplantation (BMT/HSCT) and enzyme replacement therapy (ERT), changed the natural history of many MPS types. However, some challenges still remain, including the prevention of cognitive decline which occurs in some MPS. Newer approaches, such as intratechal ERT, substrate reduction therapy, read-through, gene therapy and encapsulated modified cells may provide a better outcome for these diseases in the near future. As early diagnosis and early treatment seems to improve treatment outcomes, and as newborn screening is now technically feasible, pilot programs (including one in progress in an area with high-incidence of MPS VI in northeastern Brazil) should provide information about its potential impact in reducing the morbidity associated with MPS diseases.

Cardiac disease in patients with mucopolysaccharidosis: presentation, diagnosis and management

The mucopolysaccharidoses (MPSs) are inherited lysosomal storage disorders caused by the absence of functional enzymes that contribute to the degradation of glycosaminoglycans (GAGs). The progressive systemic deposition of GAGs results in multi-organ system dysfunction that varies with the particular GAG deposited and the specific enzyme mutation(s) present. Cardiac involvement has been reported in all MPS syndromes and is a common and early feature, particularly for those with MPS I, II, and VI. Cardiac valve thickening, dysfunction (more severe for left-sided than for right-sided valves), and hypertrophy are commonly present; conduction abnormalities, coronary artery and other vascular involvement may also occur. Cardiac disease emerges silently and contributes significantly to early mortality.The clinical examination of individuals with MPS is often difficult due to physical and, sometimes, intellectual patient limitations. The absence of precordial murmurs does not exclude the presence of cardiac disease. Echocardiography and electrocardiography are key diagnostic techniques for evaluation of valves, ventricular dimensions and function, which are recommended on a regular basis. The optimal technique for evaluation of coronary artery involvement remains unsettled.Standard medical and surgical techniques can be modified for MPS patients, and systemic therapies such as hematopoietic stem cell transplantation and enzyme replacement therapy (ERT) may alter overall disease progression with regression of ventricular hypertrophy and maintenance of ventricular function. Cardiac valve disease is usually unresponsive or, at best, stabilized, although ERT within the first few months of life may prevent valve involvement, a fact that emphasizes the importance of early diagnosis and treatment in MPS.

Impaired sulphated glycosaminoglycan metabolism in a patient with GM-2 gangliosidosis (Tay-Sachs disease)

An abnormal urinary excretion of sulphated glycosaminoglycans in a patient with GM-2 gangliosidosis (Tay-Sachs disease) is described. Besides the accumulation of GM-2 ganglioside in liver and lack of hexosaminidase A, the patient shows an abnormal urinary excretion of an iduronic acid-rich low molecular weight heparan sulphate. Also, no dermatan sulphate could be detected in the urine, whereas this compound was the main sulphated glycosaminoglycan in the liver of the patient. Heparan sulphate was the main glycosaminoglycan of normal liver. The total amount of sulphated glycosaminoglycans in the urine and liver of the patient did not differ significantly from the amounts found in the liver and urine of normal subjects. Several plasma glycosidases have been assayed and the activities did not differ significantly from the values obtained for the plasma of normal subjects.

Retinitis pigmentosa and colon cancer: a previously unreported association

Retinitis pigmentosa, a hereditary disease characterized by progressive retinal degeneration and blindness, has been associated with numerous diseases. We report the first association between retinitis pigmentosa and colon cancer in 3 of 53 hospitalized patients with retinitis pigmentosa at the Massachusetts General Hospital and Massachusetts Eye and Ear Infirmary for the period from 1962 to 1977.

Electron microscopy: a method for the diagnosis of inherited metabolic storage diseases. Electron microscopy in diagnosis

In the diagnosis of inherited metabolic diseases, electron microscopy has become an important method complementary to clinical, histological and biochemical assays. The characteristic ultrastructure of stored material as well as the site of accumulation in the cell are shown in a number of metabolic disorders. The most prominent advantages of electron microscopical techniques as compared to alternative techniques are discussed. One of the advantages is the fact that ultrastructural investigation requires only tissue samples of very small size, and another that its results may be obtained within two days. Moreover, transmission electron microscopy permits new and promising analytical methods such as quantitative estimation of organellar changes (morphometry) and energy dispersive X-ray elemental analysis (EDX).

[Mucolipidosis type II. Report of 2 suggestive cases]

The clinical and laboratorial study of two brothers with gargoylism is reported. The examination of the urine showed normal findings of mucopolysaccharides. The authors made differential diagnoses with others mucolipidoses and concluded that mucolipidose type II should be considered in any patient with gargoylism.

Endoneurial lipid composition of normal human sural nerve

The endoneurial lipid composition was determined in 7 human sural nerves from subjects without known neurological disease. The nerves were morphologically normal, with myelinated fiber density of 7,710 +/- 1,210/mm2 (mean +/- SD). Endoneurium contained 30.7 +/- 1.5 mg total lipid per 100 mg of dry weight. Cholesterol was the predominant lipid (9.1 +/- 1.0 mg). Cholesterol ester was present only in very small quantities (0.2 +/- 0.1 mg). Cerebroside concentration was 4.5 +/- 0.3 mg, and sulfatide was 1.5 +/- 0.3 mg. The most abundant phospholipid was sphingomyelin (4.3 +/- 0.3 mg), followed by phosphatidylethanolamine (4.1 +/- 0.2 mg), phosphatidylcholine (3.8 +/- 0.2 mg), and phosphatidylinositol-phosphatidylserine (1.7 +/- 0.2 mg). Eighty-one percent of cerebroside nonhydroxy fatty acids were long chain (C20 to C26), and 67% were saturated. Technological advances now permit microchemical lipid analysis of human sural nerve biopsies in cases of neuropathy. When compared with our normative data, such studies may further the understanding of peripheral nerve disorders.

A new type of mucolipidosis associated with hereditary thrombocytopathy and color blindness

Autopsy findings of a 22-year-old Japanese male who showed the symptoms of both mucopolysaccharidosis and sphingolipidosis are reported. The patient had a gargoyle-like face, bone change with cherry-red spot and absence of mucopolysacchariduria, and moreover accompanied by hereditary thrombocytopathy and color blindness. Autopsy findings were almost the same as those of mucopolysaccharidosis, histochemically and electron microscopically. Unique findings were, however, present in the hepatocytes, another inclusion containing dense fine granuloreticular structures was found electron microscopically. Some foamy cells in the lymph nodes, liver including sinusiodal cells, bone marrow and spleen contained intracytoplasmic sudanophilic substance in the form of moderate electron dense globules by electron microscopy. The outstanding finding of the enzymatic activity was the decrease of beta-galactosidase in the liver and brain.

Generalized gangliosidosis: acid beta-galactosidase deficiency with early onset, rapid mental deterioration and minimal bone dysplasia

This report concerns a 3-month-old girl with rapidly progressive psychomotor retardation, hepatomegaly, vacuolated lymphocytes, minimal bone dysplasia and normal excretion of acid mucopolysaccharides. A deficiency of acid beta-galactosidase was demonstrated in isolated leucocytes and in a liver biopsy. The diagnosis of generalized gangliosidosis due to deficiency of beta-galactosidase was also based on the absence of the enzyme activity from cultured fibroblasts. The diagnosis was confirmed on autopsy at 16 months by typical histology, electron microscopy and biochemistry of the organs. beta-galactosidase deficiency has been demonstrated in various clinical conditions ranging from generalized gangliosidosis with severe mental retardation to clinical pictures resembling Morquio's disease and normal intelligence. The heterogeneity of the clinical manifestations in beta-galactosidase deficiency could be explained by different residual activities of a structurally mutated enzyme towards its various substrates.

Clinical and biochemical expression of a unique mucopolysaccharidosis

A boy who presented with painful joints leading to contractures was found to have a mucopolysaccharidosis not previously described. He had severe dysostosis multiplex of the long bones but nearly normal intellectual development and no involvement of the cornea. Lysosomal storage vacuoles were noted in dermal endothelial cells; these were similar to those seen in the genetic mucopolysaccharidoses. Mucopolysacchariduria was not excessive in amount but it was distinctly abnormal in pattern and his excretion of dermatan sulfate resembled that found in the Hunter and Hurler syndromes. The activities of the lysosomal hydrolases in cultured fibroblasts were normal or increased. The degradation of accumulated 35S-mucopolysaccharide in fibroblasts in culture was typical of a mucopolysaccharidosis. His mother accumulated 35S-mucopolysaccharides in fibroblasts, suggesting an X-linked inheritance of the disorder.

Retinitis pigmentosa

The authors review the symptomatic and genetic aspects of the various entities of isolated retinitis pigmentosa (R.P), both in its typical form and in the forms associated with the affection of other ocular tissues. Syndromes in which R. P. is associated with the affection of other organs and systemic disorders are also cconsidered. Origin, diagnosis and the course of the disease are discussed with regard to electrophysiology, histopathology, fluorescein angiography and biochemistry. Animal research has provided new realizations about the ultrastructure and physiological mechanisms of retinal photoreceptors, and better understanding of abnormal changes. The possible pathogenesis of the human disease, based on research findings, is onsidered. Although R.P. is generally thought to be to be an "untreatable" disease, therapy may be effective in several pathological entities. Methods and results of therapy with vitamins, light deprivation and vision aids are discussed.

The diagnosis of mucopolysaccharidoses by electron microscopy of skin biopsies

An ultrastructural examination was carried out on the skin of six children suffering from Mucopolysaccharidosis I (MPSI or Hurler's disease) and MPS II (Hunter's disease). Both intracellular mucopolysaccharides and lipids were observed. The dermal cells, i.e. fibroblasts, macrophages, were loaded with multiple vacuolar inclusions thought to be of lysosomal origin. They appeared either content-free or filled with granular, fuzzy and/or pseudomyelinic structures. Identical abnormalities were observed within the Schwann cells, smooth muscle cells and keratinocytes. Mast cells showed peculiar "worm-like" inclusions apart from their normal granulations. Since ultrastructure of a skin sample may provide as much data as brain, liver or kidney, cutaneous electron microscopy can be recommended to confirm a diagnosis of MPS.

The cerebellum in mucopolysaccharidosis. A histological, histochemical, and ultrastructural study

Studies in the morphology, histochemistry, and ultrastructure of the cerebellum, with special reference to the Purkinje cell dendrites, have been undertaken in eight cases of gargoylism. The results suggest that the demonstration of ovoid swellings of the Purkinje cell dendrites by the Cajal method for the cerebellum, together with certain histochemical findings, may enable a diagnosis of mucopolysaccharidosis to be made. Possible mechanisms for the formation of these swellings are briefly discussed.

The Hurler syndrome: a study of cultured lymphoid cell lines

Lymphoid suspension lines have been established from three patients with the Hurler syndrome and four normals. The Hurler lines can be distinguished from normals by (a) staining characteristics, (b) increase in total cellular mucopolysaccharide content, and (c) increase in dermatan sulfate. Hyaluronic acid is absent in cultured lymphoid cells from normal persons and patients with the Hurler syndrome. The availability of biochemically marked suspension cultures should prove useful for enzymatic studies as well as for further elucidation of this clinical syndrome.

Correction of celluar metachromasia in cultured fibroblasts in several inherited mucopolysaccharidoses

Cultured fibroblasts from the genetic mucopolysaccharidoses store higher than normal amounts of the polyanionic glycosaminoglycans (mucopolysaccharides); histochemical staining with the cationic dyes toluidine blue O and Alcian blue detects such intracellular accumulation. With these stains as phenotypic markers, correction of the cellular abnormality by fibroblasts derived from different patients and their heterozygous parents has been observed among several genetic types of mucopolysaccharidoses. In this way, syndromes previously considered clinically homogeneous have been separated into distinct groups.