Clinical features and health-related quality of life in adult patients with mucopolysaccharidosis IVA: the Spanish experience

Mucopolysaccharidosis IVA: Current Disease Models and Drawbacks

Mucopolysaccharidosis IVA (MPS IVA) is a rare disorder caused by mutations in the N-acetylgalactosamine-6-sulfate-sulfatase (GALNS) encoding gene. GALNS leads to the lysosomal degradation of the glycosaminoglyccreasans keratan sulfate and chondroitin 6-sulfate. Impaired GALNS enzymes result in skeletal and non-skeletal complications in patients. For years, the MPS IVA pathogenesis and the assessment of promising drugs have been evaluated using in vitro (primarily fibroblasts) and in vivo (mainly mouse) models. Even though value information has been raised from those studies, these models have several limitations. For instance, chondrocytes have been well recognized as primary cells affected in MPS IVA and responsible for displaying bone development impairment in MPS IVA patients; nonetheless, only a few investigations have used those cells to evaluate basic and applied concepts. Likewise, current animal models are extensively represented by mice lacking GALNS expression; however, it is well known that MPS IVA mice do not recapitulate the skeletal dysplasia observed in humans, making some comparisons difficult. This manuscript reviews the current in vitro and in vivo MPS IVA models and their drawbacks.

Mucopolysaccharidoses: Cellular Consequences of Glycosaminoglycans Accumulation and Potential Targets

Mucopolysaccharidoses (MPSs) constitute a heterogeneous group of lysosomal storage disorders characterized by the lysosomal accumulation of glycosaminoglycans (GAGs). Although lysosomal dysfunction is mainly affected, several cellular organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, and their related process are also impaired, leading to the activation of pathophysiological cascades. While supplying missing enzymes is the mainstream for the treatment of MPS, including enzyme replacement therapy (ERT), hematopoietic stem cell transplantation (HSCT), or gene therapy (GT), the use of modulators available to restore affected organelles for recovering cell homeostasis may be a simultaneous approach. This review summarizes the current knowledge about the cellular consequences of the lysosomal GAGs accumulation and discusses the use of potential modulators that can reestablish normal cell function beyond ERT-, HSCT-, or GT-based alternatives.

Understanding the challenges, unmet needs, and expectations of mucopolysaccharidoses I, II and VI patients and their caregivers in France: a survey study

BACKGROUND

Mucopolysaccharidoses (MPS) are a group of inherited lysosomal storage diseases caused by defective enzyme activity involved in the catalysis of glycosaminoglycans. Published data on adult patients with MPS remains scarce. Therefore, the present qualitative survey study was aimed at understanding knowledge of the disease, unmet needs, expectations, care, and overall medical management of adult/adolescent patients with MPS I, II and VI and their caregivers in France.

RESULTS

A total of 25 patients (MPS I, n_p = 11; MPS II, n_p = 9; MPS VI, n_p = 5) were included and about 36 in-depth interviews (caregivers alone, n_c = 8; patients-caregiver pair, n_c+p = 22; patients alone, n_p = 6) were conducted. Except one (aged 17 years), all patients were adults (median age: 29 years [17-50]) and diagnosed at median age of 4 years [0.4-30], with mainly mothers as caregivers (n_c = 16/19). Patients were classified into three groups: Group A, Patients not able to answer the survey question because of a severe cognitive impairment (n_p = 8); Group B, Patients able to answer the survey question with low or no cognitive impairment and high motor disability (n_p = 10); and Group C, Patients able to answer the survey question with low or no cognitive impairment and low motor disability (n_p = 7). All groups were assessed for impact of disease on their daily lives based on a scale of 0-10. Caregivers in Group A were found to be most negatively affected by the disease, except for professional activity, which was most significantly impacted in Group B (4.7 vs. 5.4). The use of orthopaedic/medical equipments, was more prevalent in Groups A and B, versus Group C. Pain management was one of the global unmet need expressed by all groups. Group A caregivers expected better support from childcare facilities, disability clinics, and smooth transition from paediatric care to adult medicine. Similarly, Group B caregivers expected better specialised schools, whereas Group C caregivers expected better psychological support and greater flexibility in weekly infusion schedules for their patients.

CONCLUSIONS

The survey concluded that more attention must be paid to the psychosocial status of patients and caregivers. The preference for reference centre for follow-up and treatment, hospitalizations and surgeries were evident. The most significant needs expressed by the patients and caregivers include better understanding of the disease, pain management, monitoring of complications, flexibility in enzyme replacement therapy, home infusions especially for attenuated patients, and improved transitional support from paediatric to adult medicine.

A novel splicing variant in GALNS in mucopolysaccharidosis IVA and the necessity of re-evaluating primer sequences

Mucopolysaccharidosis type IVA (MPS IVA; Morquio syndrome type A) is an autosomal recessive disorder caused by defects in the lysosomal hydrolase N-acetylgalactosamine-6-sulfatase (GALNS) gene, leading to progressive systemic skeletal dysplasia. Early diagnosis and early intervention with enzyme replacement therapy are crucial for improving outcomes in these patients. However, a relatively high number of patients are genetically undiagnosed due to high allelic heterogeneity and the absence of robust functional evidence for most variants of the GALNS gene. Herein, we report a novel intronic variant identified with RNA analysis and an allele dropout (ADO) event caused by a common benign variant in the primer-binding site in a Korean boy with MPS IVA. A 28-month-old boy presented with pectus carinatum, kyphoscoliosis, and joint hypermobility with multiple skeletal dysplasia involving the vertebrae and hip joint. Total urinary glycosaminoglycans were elevated with a predominant keratan sulfate fraction, and GALNS (EC 3.1.6.4) activity was significantly decreased in leukocytes. Sanger sequencing was performed; however, only one heterozygous intronic variant with uncertain clinical significance, c.566+3A > T (p.(?)), was identified. As the patient exhibited clinical and biochemical features of MPS IVA, we conducted whole genome sequencing (WGS) of the patient and his family to clarify the molecular diagnosis. WGS revealed a compound heterozygous genotype, c.1019G > A (p.(Gly340Asp)) and c.566+3A > T (p.(?)), in the GALNS gene. On mRNA sequencing, c.566+3A > T, was confirmed to cause exon 5 skipping and a premature stop codon. With subsequent investigation, we discovered that the variant, c.1019G > A, was undetected on initial sequencing because of ADO due to a common benign variant (rs3859024:G > C) at the primer annealing location. We present a novel intronic variant with a splicing defect in the GALNS gene and suggest that clinicians review primer sequences in cases not diagnosed on Sanger sequencing before progressing to diagnostic steps such as WGS.