title: Practical and reliable enzyme test for the detection of mucopolysaccharidosis IVA (Morquio Syndrome type A) in dried blood samples.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Medical Genetics Service, Hospital de Clínicas de Porto Alegre, RS, Brazil.
authors.forename: Marli V
authors.initials: MV
authors.lastname: Camelier
authors.forename: Maira G
authors.initials: MG
authors.lastname: Burin
authors.forename: Jurema
authors.initials: J
authors.lastname: De Mari
authors.forename: Taiane A
authors.initials: TA
authors.lastname: Vieira
authors.forename: Giórgia
authors.initials: G
authors.lastname: Marasca
authors.forename: Roberto
authors.initials: R
authors.lastname: Giugliani
mesh_terms: D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D006801:Humans; D008875:Middle Aged; D009085:Mucopolysaccharidosis IV / Q000097:blood / Q000175:diagnosis*; D015203:Reproducibility of Results; D055815:Young Adult