Case report

Perioperative Implications of Morquio Syndrome in a 31-Year-Old Woman Undergoing Aortic Valve Replacement

Mucopolysaccharidosis IVA (MPS IVA, Morquio A syndrome) is an autosomal recessive disorder caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase. Deficiency of this enzyme leads to the accumulation of specific glycosaminoglycans (GAGs), chondroitin-6-sulfate (C6S) and keratan sulfate (KS), which are mainly synthesized in the cartilage. Therefore, the substrates are stored primarily in the cartilage and its extracellular matrix (ECM), leading to a direct impact on bone development and successive systemic skeletal spondylepiphyseal dysplasia. The skeletal-related symptoms for MPS IVA include short stature with short neck and trunk, odontoid hypoplasia, spinal cord compression, tracheal obstruction, obstructive airway, pectus carinatum, restrictive lung, kyphoscoliosis, platyspondyly, coxa valga, genu valgum, waddling gait, and laxity of joints. The degree of imbalance of growth in bone and other organs and tissues largely contributes to unique skeletal dysplasia and clinical severity. Diagnosis of MPS IVA needs clinical, radiographic, and laboratory testing to make a complete conclusion. To diagnose MPS IVA, total urinary GAG analysis which has been used is problematic since the values overlap with those in age-matched controls. Currently, urinary and blood KS and C6S, the enzyme activity of GALNS, and GALNS molecular analysis are used for diagnosis and prognosis of clinical phenotype in MPS IVA. MPS IVA can be diagnosed with unique characters although this disorder relates closely to other disorders in some characteristics.

In this review article, we comprehensively describe clinical, radiographic, biochemical, and molecular diagnosis and clinical assessment tests for MPS IVA. We also compare MPS IVA to other closely related disorders to differentiate MPS IVA. Overall, imbalance of growth in MPS IVA patients underlies unique skeletal manifestations leading to a critical indicator for diagnosis.

We describe 2 adult sisters with type I mucopolysaccharidosis (MPS) who underwent combined mitral and aortic valve replacement for mitral and aortic valve stenosis. One died early postoperatively and the other survived but had a repeat double-valve replacement 1 month after the first. We analyzed previously reported patients with MPS and valve replacement to learn of their outcomes. The study of our 2 patients and those previously reported suggests that valve replacement in patients with MPS should be viewed with extreme caution.

Morquio syndrome, a congenital mucopolysaccharidosis, presents several challenges for the provision of effective labor analgesia. We report the case of a woman admitted for induction of labor who received an early epidural and subsequently required cesarean delivery. Optimal bilateral labor analgesia was not achieved despite multiple adjustments, and systemic analgesia was needed for cesarean delivery.

La maladie de Morquio A, ou mucopolysaccharidose de type IV (Morquio A syndrome ; MPS IVA ; OMIM 253000), est une maladie multi-systémique, grave et extrêmement invalidante, mettant en jeu le pronostic vital ; elle est liée à un déficit enzymatique en N-acétylgalactosamine-6-sulfate sulfatase (GALNS), enzyme lysosomiale responsable de la dégradation du kératane sulfate (KS) et du chondroïtine-6-sulfate (C6S). Cette maladie se caractérise par des manifestations pulmonaires, respiratoires et une atteinte osseuse, avec atteinte spondylo-épimétaphysaire progressive, et des complications ophtalmologiques, auditives et cardiaques plus modérées et tardives. L’ensemble de ces manifestations réduisent progressivement la mobilité des patients. On distingue les formes sévères, découvertes avant 1 an, des formes intermédiaires (découvertes entre 1 et 5 ans) et des formes atténuées, découvertes après 5 ans (parfois beaucoup plus tard). Les principaux signes sont les déformations osseuses, avec pectus carinatum, cyphoscoliose et genu valgum, et un infléchissement statural précoce, entraînant rapidement un quasi-arrêt de la croissance. Le développement cognitif des patients est normal. Les signes radiologiques sont assez spécifiques, avec une platyspondylie particulière, un raccourcissement des os longs et une atteinte caractéristique du bassin. Le diagnostic, orienté par le dosage des GAG urinaires, est confirmé par l’étude enzymatique de la GALNS. Le conseil génétique est important dans le cadre de cette affection autosomique récessive et le diagnostic moléculaire permet de proposer, pour les couples qui le souhaitent, un diagnostic prénatal. La prise en charge est essentiellement symptomatique, avec détection précoce et correction orthopédique des troubles de la statique dorsale et des membres inférieurs, prise en charge ORL et respiratoire, et accompagnement psychologique et socio-éducatif de l’enfant et sa famille.

Type IV mucopolysaccharidosis (Morquio A syndrome; MPS IVA; OMIM 253000), is a multisystemic, severe and very disabling disease, also life-threatening; MPS IVA is due to a deficiency of the enzyme N-acetylgalactosamine-6-sulfate sulfatase (GALNS), a lysosomal enzyme responsible for the degradation of keratan sulfate (KS) and chondroitin-6-sulfate (C6S). The disease is characterized by respiratory, pulmonary manifestations and also causes bone involvement with progressive spondyloepimetaphyseal degradation and mild and late-onset ophthalmologic, hearing and cardiac complications. These manifestations progressively impair the patients’ physical mobility. Severe forms of the disease, diagnosed before the age of 1 year, can be distinguished from intermediary (diagnosed between 1 and 5 years old) and attenuated disease, diagnosed after the age of 5 years (occasionally far later). The main signs are bone deformities namely pectus carinatum, kyphoscoliosis and genu valgum, with early flattening of the growth curve, leading rapidly to almost complete growth arrest. Patients have normal cognitive development. The radiological signs are relatively specific with, in particular, platyspondyly, shortening of the long bones and characteristic pelvic changes. The diagnosis is suggested by elevated urinary GAGs level and profile, and is confirmed by GALNS enzymatic studies on molecular testing. Genetic counseling is important in this autosomal recessive disorder and enzymatic and/or molecular testing can be offered for prenatal diagnosis. Management is mostly symptomatic, based on early detection and orthopedic correction of spine and lower limb deformities, ENT and respiratory management and psychological, social and educational support for the child and his/her family.

Mucopolysaccharidosis type IVA (MPS IVA) was described in 1929 by Luis Morquio from Uruguay and James Brailsford from England, and was later found as an autosomal recessive lysosomal storage disease. MPS IVA is caused by mutations in the gene encoding the enzyme, N-acetylgalactosamine-6-sulfate sulfatase (GALNS). Reduced GALNS activity results in impaired catabolism of two glycosaminoglycans (GAGs), chondroitin-6-sulfate (C6S) and keratan sulfate (KS). Clinical presentations of MPS IVA reflect a spectrum of progression from a severe “classical” phenotype to a mild “attenuated” phenotype. More than 180 different mutations have been identified in the GALNS gene, which likely explains the phenotypic heterogeneity of the disorder.

Accumulation of C6S and KS manifests predominantly as short stature and skeletal dysplasia (dysostosis multiplex), including atlantoaxial instability and cervical cord compression. However, abnormalities in the visual, auditory, cardiovascular, and respiratory systems can also affect individuals with MPS IVA. Diagnosis is typically based on clinical examination, skeletal radiographs, urinary GAG, and enzymatic activity of GALNS in blood cells or fibroblasts. Deficiency of GALNS activity is a common assessment for the laboratory diagnosis of MPS IVA; however, with recently increased availability, gene sequencing for MPS IVA is often used to confirm enzyme results. As multiple clinical presentations are observed, diagnosis of MPS IVA may require multi-system considerations.

This review provides a history of defining MPS IVA and how the understanding of the disease manifestations has changed over time. A summary of the accumulated knowledge is presented, including information from the International Morquio Registry. The classical phenotype is contrasted with attenuated cases, which are now being recognized and diagnosed more frequently. Laboratory based diagnoses of MPS IVA are also discussed.

Mucopolysaccharidosis type IVB (MPS IVB) is a very rare lysosomal storage disorder characterized by skeletal dysplasia, hearing disorder, and cardiac valvular disease. Herein, we report an extremely rare manifestation of MPS IVB in a 60-year-old female patient who underwent a successful aortic valve replacement. The patient presented with mild coarse facial features, short stature, mild dyspnea, sternal protrusion, mild lumbar hyperlordosis, and waddling gait owing to bilateral femoral head necroses and bilateral arthrosis of the knees. The patient also suffered from dyspnea, NYHA II–III. Echocardiography revealed severe stenosis of a calcified aortic valve (AVA 0.67 cm², AVAi 0.45 cm²/m², PG max/mean 130/80 mmHg), left ventricular hypertrophy with predominant septal thickening (18 mm) and mild left ventricle outflow tract obstruction at rest, mild mitral valve regurgitation, and dilated ascending aorta (36 mm, 26.5 mm/m²). Dyspnea resolved after septal myectomy and replacement of the aortic valve with bioprosthesis. Excretion levels and spectrum of glycosaminoglycans (GAGs) in urine were normal in the patient. We confirmed the diagnosis of MPS IVB by identifying decreased beta-galactosidase activity in isolated leukocytes (6 nmol/h/mg; controls 95–272) and by molecular genetic analyses (c.438_440delTCT and c.817_818TG>CT mutations in the GLB1 gene). Primary lysosomal storage of glycosaminoglycans was detected in fibroblasts of the aortic valve. Additional pathologies included valvular fibrosis, calcification, neovascularization, and mild chronic inflammation. In conclusion, the diagnosis of MPS IVB should be considered in older patients with cardiac valvular disease and progressive skeletal abnormality even if urinary excretion levels of GAGs are normal.