Neurocognition across the spectrum of mucopolysaccharidosis type I: Age, severity, and treatment

Cognitive outcomes and age of detection of severe mucopolysaccharidosis type 1

The US Secretary of Health and Human Services recommended in February 2016 that mucopolysaccharidosis type 1 (MPS I) be added to the recommended uniform screening panel for state newborn screening programs. One of the key factors in this decision was the evidence suggesting that earlier treatment with hematopoietic cell transplantation (HCT) for the most severe form, Hurler syndrome (MPS IH), would lead to improved cognitive outcomes. Consistent evidence from peer-reviewed studies suggests that transplantation in the first year of life is associated with improved developmental quotient or intelligence quotient and continued cognitive growth, with earlier age of treatment associated with improved outcomes. However, available evidence suggests that cognitive functioning and attention can still lag behind unaffected age-matched children, leading to the need for special education services. Verbal and nonverbal cognitive abilities outcomes may be affected differently by HCT. With the recent addition of MPS I to the recommended uniform screening panel, future work is needed to evaluate the impact of earlier, presymptomatic detection and treatment initiation and other supportive therapies on cognitive outcomes.Genet Med advance online publication 26 January 2017.

A longitudinal study of emotional adjustment, quality of life and adaptive function in attenuated MPS II

OBJECTIVES

The behavioral, adaptive and quality of life characteristics of attenuated mucopolysaccharidosis type II (MPS II) have not been well studied. Understanding changes over time in the attenuated phenotype may assist in helping achieve better outcomes in long-term function. This longitudinal study investigates these outcomes in relation to age, somatic disease burden, and IQ. Specifically, somatic disease burden is a major challenge for these patients, even with treatment with enzyme replacement therapy.

METHODS

15 patients, 10 between ages 6 and < 12 and 5 between ages ≥ 12 and 18, were selected who had at least 2 yearly visits. The occurrence of physical signs, the Physical Symptom Score, and IQ in these two groups was studied as well as the longitudinal association of age with standardized measures of quality of life, adaptive function, and behavioral symptoms as rated by parents and the child's self-report. Slopes by age across and within patients were calculated for these measures.

RESULTS

All but one child had hearing loss, most had joint contractures and short stature. Somatic disease burden increased with age. IQ, although normal for most, also improved with age in those under 12 years of age. Physical quality of life decreased while psychosocial quality of life increased with age. Although other adaptive skills were in the broad average range, daily living skills were low at baseline relative to normative data and decreased over time. Behavior ratings indicated improvement in attention and hyperactivity over time. No patient had severe psychopathology, but older children reported an increasing sense of inadequacy and low self-esteem on self-report, presumably due to increasing awareness of differences from peers over time.

CONCLUSIONS

Attenuated MPS II patients have increasing somatic disease burden and poor physical quality of life as they develop as well as decreasing self-esteem and sense of adequacy. Psychosocial quality of life, adaptive skills, and attention improve. Recognition of and intervention around these issues will be beneficial to MPS II attenuated patients who have the resources to use such assistance to improve their long-term outcomes.

Emerging tools to study proteoglycan function during skeletal development

In the past 20years, appreciation for the varied roles of proteoglycans (PGs), which are specific types of sugar-coated proteins, has increased dramatically. PGs in the extracellular matrix were long known to impart structural functions to many tissues, especially articular cartilage, which cushions bones and allows mobility at skeletal joints. Indeed, osteoarthritis is a debilitating disease associated with loss of PGs in articular cartilage. Today, however, PGs have a demonstrated role in cell biological processes, such as growth factor signalling, prompting new perspectives on the etiology of PG-associated diseases. Here, we review diseases associated with defects in PG synthesis and sulfation, also highlighting current understanding of the underlying genetics, biochemistry, and cell biology. Since most research has analyzed a class of PGs called heparan sulfate PGs, more attention is paid here to studies of chondroitin sulfate PGs (CSPGs), which are abundant in cartilage. Interestingly, CSPG synthesis is tightly linked to the cell biological processes of secretion and lysosomal degradation, suggesting that these systems may be linked genetically. Animal models of loss of CSPG function have revealed CSPGs to impact skeletal development. Specifically, our work from a mutagenesis screen in zebrafish led to the hypothesis that cartilage PGs normally delay the timing of endochondral ossification. Finally, we outline emerging approaches in zebrafish that may revolutionize the study of cartilage PG function, including transgenic methods and novel imaging techniques. Our recent work with X-ray fluorescent imaging, for example, enables direct correlation of PG function with PG-dependent biological processes.

Association of somatic burden of disease with age and neuropsychological measures in attenuated mucopolysaccharidosis types I, II and VI

INTRODUCTION

The mucopolysaccharidoses (MPSs) are a group of rare genetic lysosomal disorders with progressive multisystem involvement. An MPS-specific physical symptom scale was developed and introduced a Physical Symptom Score (PSS) to quantify the somatic disease burden across MPS I, II and VI.

HYPOTHESIS

Somatic burden of disease in patients with attenuated MPS I, II and VI as measured by the PSS will be positively associated with age and negatively associated with neuropsychological functions [i.e. full scale intelligence quotient (FSIQ) and attention].

MATERIALS AND METHODS

Forty-eight patients with attenuated MPS I (n = 24), II (n = 14), and VI (n = 10) aged 6 to 32 years on enzyme replacement therapy who were enrolled in "Longitudinal Studies of Brain Structure and Functions in MPS Disorders" across seven centers. Somatic disease burden was measured by the PSS. Neuropsychological functions were measured by the Wechsler Abbreviated Scale of Intelligence (WASI) and Test of Variables of Attention (TOVA).

RESULTS

PSS was positively associated with age in attenuated MPS I (P < 0.001), MPS II (P < 0.01) and MPS VI (P < 0.05). There was a negative association of PSS with FSIQ in attenuated MPS I (P < 0.001) and in MPS VI (P < 0.001) but not with MPS II. Although attention scores were below average in all groups, a significant negative association between PSS and one measures of sustained attention (TOVA d prime) was found only in MPS VI.

CONCLUSIONS

Physical Symptom Score increased with age in attenuated MPS I, II and VI, reflecting progressive somatic burden of disease despite treatment with enzyme replacement therapy. Furthermore, the association of increased somatic disease burden with decreased neurocognitive ability suggests that both measures reflect disease severity and are not independent.