Practical and reliable enzyme test for the detection of mucopolysaccharidosis IVA (Morquio Syndrome type A) in dried blood samples.

BACKGROUND: Mucopolysaccharidosis IVA (MPS IVA), or Morquio Syndrome type A, is an autosomal recessive disease caused by deficiency of the lysosomal enzyme N-acetylgalactosamine-6-sulfatase (GALNS), resulting in excessive lysosomal storage of keratan sulfate in many tissues and organs. This accumulation causes a severe skeletal dysplasia with short stature, and affects the eye, heart and other organs, with many signs and symptoms. Morquio A syndrome is estimated to occur in 1 in 200,000 to 300,000 live births. Clinical trials with enzyme replacement therapy for this disease are in progress, and it is probable that the treatment, when available, would be more effective if started early. We describe an innovative fluorometric method for the assay of GALNS in dried blood spots (DBS). METHODS: We used dried blood spots (DBS) as the enzyme source and compared it with leukocytes samples, having studied 25 MPS IVA patients and 54 healthy controls. We optimized the assay conditions, including incubation time and stability of DBS samples. To eppendorf type tubes containing a 3-mm diameter blood spot we added elution liquid and substrate solution. After 2 different incubations at 37°C, the amount of hydrolyzed product was compared with a calibrator to allow the quantification of the enzyme activity. Results in DBS were compared to the ones obtained in leukocytes using the standard technique. RESULTS: The fluorescent methodology was validated in our laboratory and the assay was found sensitive and specific, allowing reliable detection of MPS IVA patients. The use of DBS simplifies the collection and transport steps, and is especially useful for testing patients from more remote areas of large countries, and when samples need to cross country borders. CONCLUSION: This assay could be easily incorporated into the protocol of reference laboratories and play a role in the screening for MPS IVA, contributing to earlier detection of affected patients.

Expression of the disease on female carriers of X-linked lysosomal disorders: a brief review.

Most lysosomal diseases (LD) are inherited as autosomal recessive traits, but two important conditions have X-linked inheritance: Fabry disease and Mucopolysaccharidosis II (MPS II). These two diseases show a very different pattern regarding expression on heterozygotes, which does not seem to be explained by the X-inactivation mechanism only. While MPS II heterozygotes are asymptomatic in most instances, in Fabry disease most of female carriers show some disease manifestation, which is sometimes severe. It is known that there is a major difference among X-linked diseases depending on the cell autonomy of the gene product involved and, therefore, on the occurrence of cross-correction. Since lysosomal enzymes are usually secreted and uptaken by neighbor cells, the different findings between MPS II and Fabry disease heterozygotes can also be due to different efficiency of cross-correction (higher in MPS II and lower in Fabry disease). In this paper, we review these two X-linked LD in order to discuss the mechanisms that could explain the different rates of penetrance and expressivity observed in the heterozygotes; this could be helpful to better understand the expression of X-linked traits.

Prospective study of 11 Brazilian patients with mucopolysaccharidosis II.

OBJECTIVE: To assess the progression of mucopolysaccharidosis II in 11 Brazilian patients over a 12-month period. METHODS: Eleven Brazilian patients with mucopolysaccharidosis II were prospectively studied at the Division of Medical Genetics of Hospital de Clínicas de Porto Alegre. The initial assessment and the assessment at 12 months included: anamnesis, physical examination, abdominal nuclear magnetic resonance, echocardiogram, 6-minute walk test, audiometry, serum biochemical tests and urinary glycosaminoglycan concentration. RESULTS: The major findings after comparing the assessments were: 1) two patients had growth retardation; 2) two patients showed negative weight change; 3) one patient went from obese to overweight; 4) three patients revealed left ventricle hypertrophy; of these, two increased the number of cardiac valve lesions; 5) there was no statistically significant difference between the mean distances obtained on the 6-minute walk test; 6) there was splenic enlargement; 7) there was an increase in gamma-glutamyltransferase levels; 8) the urinary concentration of glycosaminoglycans remained unchanged. CONCLUSIONS: In general, echocardiographic findings were the only variable with deterioration and possible immediate clinical consequences. Although a 12-month period is too short to detect changes in most variables related to mucopolysaccharidosis II, its progressive nature should be taken into account when evaluating the efficiency of treatment protocols.

Prospective study of 11 Brazilian patients with mucopolysaccharidosis II

OBJETIVO: Avaliar a progressão da mucopolissacaridose II, durante um período de 12 meses, em 11 pacientes brasileiros. MÉTODOS: Onze pacientes brasileiros com mucopolissacaridose II foram avaliados prospectivamente no Serviço de Genética Médica do Hospital de Clínicas de Porto Alegre. As avaliações realizadas na visita inicial e na de 12 meses foram: anamnese, exame físico, ressonância nuclear magnética abdominal, ecocardiograma, teste da caminhada em 6 minutos, audiometria, exames bioquímicos séricos e dosagem uriná- ria de glicosaminoglicanos. RESULTADOS: Os principais achados relativos à comparação entre as duas visitas foram: 1) dois pacientes apresentaram retardo de crescimento; 2) dois pacientes apresentaram variação negativa em relação ao peso; 3) um paciente apresentou variação de obesidade para sobrepeso; 4) três pacientes desenvolveram alargamento do ventrículo esquerdo; destes, dois aumentaram o número de lesões nas valvas cardíacas; 5) não foi encontrada diferença estatística significativa entre a média das distâncias percorridas no teste da caminhada em 6 minutos; 6) houve aumento do volume esplênico; 7) ocorreu aumento dos níveis de gamaglutamiltransferase; 8) não houve alteração dos níveis urinários de glicosaminoglicanos. CONCLUSÕES: De uma maneira geral, a única variável que apresentou, no período estudado, piora com potencial repercussão clínica imediata foram os achados ecocardiográficos. Embora o período de 12 meses seja curto para medir alterações na maioria dos parâmetros comprometidos na mucopolissacaridose II, sua natureza progressiva deve ser levada em conta na avaliação da eficácia dos protocolos de tratamento para essa condição.

OBJECTIVE: To assess the progression of mucopolysaccharidosis II in 11 Brazilian patients over a 12-month period. METHODS: Eleven Brazilian patients with mucopolysaccharidosis II were prospectively studied at the Division of Medical Genetics of Hospital de Clínicas de Porto Alegre. The initial assessment and the assessment at 12 months included: anamnesis, physical examination, abdominal nuclear magnetic resonance, echocardiogram, 6-minute walk test, audiometry, serum biochemical tests and urinary glycosaminoglycan concentration. RESULTS: The major findings after comparing the assessments were: 1) two patients had growth retardation; 2) two patients showed negative weight change; 3) one patient went from obese to overweight; 4) three patients revealed left ventricle hypertrophy; of these, two increased the number of cardiac valve lesions; 5) there was no statistically significant difference between the mean distances obtained on the 6-minute walk test; 6) there was splenic enlargement; 7) there was an increase in gamma-glutamyltransferase levels; 8) the urinary concentration of glycosaminoglycans remained unchanged. CONCLUSIONS: In general, echocardiographic findings were the only variable with deterioration and possible immediate clinical consequences. Although a 12-month period is too short to detect changes in most variables related to mucopolysaccharidosis II, its progressive nature should be taken into account when evaluating the efficiency of treatment protocols.