Gastrointestinal Manifestations in Mucopolysaccharidosis Type III: Review of Death Certificates and the Literature

BACKGROUND

Mucopolysaccharidosis type III (MPS III, Sanfilippo disease) is a life-limiting recessive lysosomal storage disorder caused by a deficiency in the enzymes involved in degrading glycosaminoglycan heparan sulfate. MPS III is characterized by progressive deterioration of the central nervous system. Respiratory tract infections have been reported as frequent and as the most common cause of death, but gastrointestinal (GI) manifestations have not been acknowledged as a cause of concern. The aim of this study was to determine the incidence of GI problems as a primary cause of death and to review GI symptoms reported in published studies.

METHODS

Causes of death from 221 UK death certificates (1957-2020) were reviewed and the literature was searched to ascertain reported GI symptoms.

RESULTS

GI manifestations were listed in 5.9% (n = 13) of death certificates. Median (IQR) age at death was 16.7 (5.3) years. Causes of death included GI failure, GI bleed, haemorrhagic pancreatitis, perforation due to gastrostomies, paralytic ileus and emaciation. Twenty-one GI conditions were reported in 30 studies, mostly related to functional GI disorders, including diarrhoea, dysphagia, constipation, faecal incontinence, abdominal pain/distension and cachexia.

CONCLUSIONS

GI manifestations may be an under-recognized but important clinical feature of MPS III. Early recognition of GI symptoms and timely interventions is an important part of the management of MPS III patients.

Comparative analysis of brain pathology in heparan sulphate storing mucopolysaccharidoses

The cause of neurodegeneration in MPS mouse models is the focus of much debate and what the underlying cause of disease pathology in MPS mice is. The timing of development of pathology and when this can be reversed or impacted is the key to developing suitable therapies in MPS. This study is the first of its kind to correlate the biochemical changes with the functional outcome as assessed using non-invasive behaviour testing across multiple mucopolysaccharidosis (MPS) mouse models. In the MPS brain, the primary lysosomal enzyme dysfunction leads to accumulation of primary glycosaminoglycans (GAGs) with gangliosides (G_M2 and G_M3) being the major secondary storage products. With a focus on the neuropathology, a time course experiment was conducted in MPS I, MPS IIIA, MPS VII (severe and attenuated models) in order to understand the relative timing and level of GAG and ganglioside accumulation and how this correlates to behaviour deficits. Time course analysis from 1 to 6 months of age was conducted on brain samples to assess primary GAG (uronic acid), β-hexosaminidase enzyme activity and levels of G_M2 and G_M3 gangliosides. This was compared to a battery of non-invasive behaviour tests including open field, inverted grid, rotarod and water cross maze were assessed to determine effects on motor function, activity and learning ability. The results show that the GAG and ganglioside accumulation begins prior to the onset of detectable changes in learning ability and behaviour. Interestingly, the highest levels of GAG and ganglioside accumulation was observed in the MPS IIIA mouse despite having 3% residual enzyme activity. Deficits in motor function were clearly observed in the severe Gus^mps/mps_, which were significantly delayed in the attenuated Gus^tm(L175F)Sly model despite their minimal increase in detectable enzyme activity. This suggests that genotype and residual enzyme activity are not indicative of severity of disease pathology in MPS disease and there exists a window when there are considerable storage products without detectable functional deficits which may allow an alteration to occur with therapy.

Disabling MNK protein kinases promotes oxidative metabolism and protects against diet-induced obesity

Objectives

Diet-driven obesity is increasingly widespread. Its consequences pose major challenges to human health and health care systems. There are MAP kinase-interacting kinases (MNKs) in mice, MNK1 and MNK2. Studies have demonstrated that mice lacking either MNK1 or MNK2 were partially protected against high-fat diet (HFD)-induced weight gain and insulin resistance. The aims of this study were to evaluate the phenotype of mice lacking both MNKs when given an HFD, to assess whether pharmacological inhibition of MNK function also protects against diet-induced obesity (DIO) and its consequences and to probe the mechanisms underlying such protection.

Methods

Male wild-type (WT) C57Bl6 mice or mice lacking both MNK1 and MNK2 (double knockout, DKO) were fed an HFD or control diet (CD) for up to 16 weeks.

In a separate study, WT mice were also given an HFD for 6 weeks, after which half were treated with the recently-developed MNK inhibitor ETC-206 daily for 10 more weeks while continuing an HFD. Metabolites and other parameters were measured, and the expression of selected mRNAs and proteins was assessed.

Results

MNK-DKO mice were almost completely protected from HFD-induced obesity. Higher energy expenditure (EE) in MNK-DKO mice was observed, which probably reflects the changes in a number of genes or proteins linked to lipolysis, mitochondrial function/biogenesis, oxidative metabolism, and/or ATP consumption. The MNK inhibitor ETC-206 also prevented HFD-induced weight gain, confirming that the activity of the MNKs facilitates weight gain due to excessive caloric consumption.

Conclusions

Disabling MNKs in mice, either genetically or pharmacologically, strongly prevents weight gain on a calorie-rich diet. This finding likely results from increased energy utilisation, involving greater ATP consumption, mitochondrial oxidative metabolism, and other processes.

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Knockout of MNK1/MNK2 protects mice against diet-induced obesity.

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MNK1/2 DKO mice have higher energy expenditure.

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MNK1/2 DKO increases the expression of genes of lipid and mitochondrial metabolism.

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Pharmacological inhibition of MNKs has similar effects.

Delayed development of ossification centers in the tibia of prenatal and early postnatal MPS VII mice

Short stature is a characteristic feature of most of the mucopolysaccharidoses, a group of inherited lysosomal storage disorders caused by a single enzyme deficiency. MPS patients present with progressive skeletal defects from an early age, including short stature due to impaired cartilage-to-bone conversion (endochondral ossification). The aim of this study was to determine which murine MPS model best reproduces the bone length reduction phenotype of human MPS and use this model to determine the earliest developmental stage when disrupted endochondral ossification first appears. Gus^mps/mps mice representing severe MPS VII displayed the greatest reduction in bone elongation and were chosen for histopathological analysis. Tibial development was assessed from E12.5 to 6 months of age. Chondrocytes in the region of the future primary ossification center became hypertrophic at a similar age to normal in the MPS VII mouse fetus, but a delay in bone deposition was observed with an approximate 1 day delay in the formation of the primary ossification centre. Likewise, chondrocytes in the region of the future secondary ossification center also became hypertrophic at the same age as normal in the MPS VII early postnatal mouse. Bone deposition in the secondary ossification centre was delayed by two days in the MPS VII proximal tibia (observed at postnatal day 14 (P14) compared to P12 in normal). The thickness of the tibial growth plate was larger in MPS VII mice from P9 onwards. Abnormal endochondral ossification starts in utero in MPS VII and worsens with age. It is characterized by a normal timeframe for chondrocyte hypertrophy but a delay in the subsequent deposition of bone in both the primary and secondary ossification centres, accompanied by an increase in growth plate thickness. This suggests that the signals for vascular invasion and bone deposition, some of which are derived from hypertrophic chondrocytes, are altered in MPS VII.

N-butyldeoxynojirimycin treatment restores the innate fear response and improves learning in mucopolysaccharidosis IIIA mice

Mucopolysaccharidosis IIIA is a heritable neurodegenerative disorder resulting from the dysfunction of the lysosomal hydrolase sulphamidase. This leads to the primary accumulation of the complex carbohydrate heparan sulphate in a wide range of tissues and the secondary neuronal storage of gangliosides GM2 and GM3 in the brain. GM2 storage is associated with CNS deterioration in the GM2 gangliosidosis group of lysosomal storage disorders and may also contribute to MPS CNS disease. N-butyldeoxynojirimycin, an inhibitor of ceramide glucosyltransferase activity and therefore of ganglioside synthesis, was administered to MPS IIIA mice both prior to maximal GM2 and GM3 accumulation (early treatment) and after the maximum level of ganglioside had accumulated in the brain (late treatment) to determine if behaviour was altered by ganglioside level. Ceramide glucosyltransferase activity was decreased in both treatment groups; however, brain ganglioside levels were only decreased in the late treatment group. Learning in the water cross maze was improved in both groups and the innate fear response was also restored in both groups. A reduction in the expression of inflammatory gene Ccl3 was observed in the early treatment group, while IL1β expression was reduced in both treatment groups. Thus, it appears that NB-DNJ elicits a transient decrease in brain ganglioside levels, some modulation of inflammatory cytokines and a functional improvement in behaviour that can be elicited both before and after overt neurological changes manifest.

SYNOPSIS

NB-DNJ improves learning and restores the innate fear response in MPS IIIA mice by decreasing ceramide glucosyltransferase activity and transiently reducing ganglioside storage and/or modulating inflammatory signals.

Coenzyme Q10 and Pyridoxal Phosphate Deficiency Is a Common Feature in Mucopolysaccharidosis Type III

Mucopolysaccharidoses (MPS) are a group of lysosomal storage disorders caused by deficiencies of lysosomal enzymes catalyzing degradation of glycosaminoglycans (GAGs). Previously, we reported a secondary plasma coenzyme Q₁₀ (CoQ) deficiency in MPS patients. For this study, nine MPS patients were recruited in the Hospital Sant Joan de Déu (HSJD, Barcelona) and two patients in the Neurometabolic Unit, National Hospital (NMU, London), to explore the nutritional status of MPS type III patients by analyzing several vitamins and micronutrients in blood and in cerebrospinal fluid. Plasma CoQ and plasma and cerebrospinal fluid pyridoxal phosphate (PLP) content were analyzed by high-pressure liquid chromatography (HPLC) with electrochemical and fluorescence detection, respectively. We found that most MPS-III patients disclosed low plasma pyridoxal phosphate (PLP) values (seven out of nine) and also low plasma CoQ concentrations (eight out of nine). We observed significantly lower median values of PLP, tocopherol, and CoQ (Mann-Whitney U test, p = 0.006, p = 0.004, and p = 0.001, respectively) in MPS patients when compared with age-matched controls. Chi-square test showed a significant association between the fact of having low plasma PLP and CoQ values in the whole cohort of patients. Cerebrospinal fluid PLP values were clearly deficient in the two patients studied. In conclusion, we report a combined CoQ and PLP deficiency in MPS-III patients. These observations could be related to the complexity of the physiopathology of the disease. If our results are confirmed in larger series of patients, CoQ and PLP therapy could be trialed as coadjuvant therapy with the current MPS treatments.

Rhodamine B and 2-acetamido-1,3,6-tri-O-acetyl-4-deoxy-4-fluoro-D-glucopyranose (F-GlcNAc) inhibit chondroitin/dermatan and keratan sulphate synthesis by different mechanisms in bovine chondrocytes

MPS disorders result from a deficiency or absence of glycosaminoglycan (GAG) degrading enzymes leading to an imbalance between the synthesis and degradation of GAGs and their subsequent accumulation in a range of cells. The inhibition of GAG synthesis using small chemical inhibitors has been proposed as a novel therapeutic approach to treatment. Several inhibitors have been shown to decrease heparan sulphate GAG synthesis and in this study we evaluated a novel fluorinated analog of N-acetylglucosamine (2-acetamido-1,3,6-tri-O-acetyl-4-deoxy-4-fluoro-D-glucopyranose (F-GlcNAc)) and rhodamine B for their ability to also inhibit the synthesis of chondroitin/dermatan and keratan sulphate GAGs present in bovine cartilage. Both inhibitors decreased GAG synthesis in chondrocyte monolayer culture and in cartilage chip explant culture in a dose dependent manner. Both inhibitors decreased the size of newly synthesised proteoglycans and in the case of F-GlcNAc this was due to a decrease in newly synthesised GAG chain size. Rhodamine B, however, did not affect GAG chain size, while both inhibitors decreased the amount of chondroitin/dermatan and keratan sulphate GAG equally. The expression of genes responsible for the initiation and elongation of chondroitin/dermatan sulphate and keratan sulphate GAGs were downregulated in the presence of rhodamine B but not in the presence of F-GlcNAc. Thus the 2 inhibitors appear to have differing effects on GAG synthesis, with F-GlcNAc inhibiting the epimerisation of UDP-GlcNAc to UDP-GalNAc thus decreasing the availability of monosaccharides for addition to the growing GAG chain, whereas rhodamine B is more likely to reduce the number of GAG chains. Together with previous data these 2 inhibitors are capable of non-specific inhibition of GAG synthesis, reducing the production of chondroitin/dermatan sulphate, keratan sulphate and heparan sulphate GAGs. As such they would be applicable to therapy in a range of MPS disorders.

Correction of mucopolysaccharidosis type IIIA somatic and central nervous system pathology by lentiviral-mediated gene transfer

BACKGROUND

The hallmark of lysosomal storage disorders (LSDs) is microscopically demonstrable lysosomal distension. In mucopolysaccharidosis type IIIA (MPS IIIA), this occurs as a result of an inherited deficiency of the lysosomal hydrolase sulphamidase. Consequently, heparan sulphate, a highly sulphated glycosaminoglycan, accumulates primarily within the cells of the reticulo-endothelial and monocyte-macrophage systems and, most importantly, neurones. Children affected by MPS IIIA experience a severe, progressive neuropathology that ultimately leads to death at around 15 years of age.

METHODS

MPS IIIA pathology was addressed in a mouse model using two separate methods of therapeutic gene delivery. A lentiviral vector expressing murine sulphamidase was delivered to 6-week-old MPS IIIA affected mice either by intravenous injection, or by intraventricular infusion. Therapeutic outcomes were assessed 7 months after gene transfer.

RESULTS

After intravenous gene delivery, liver sulphamidase was restored to approximately 30% of wild-type levels. The resultant widespread delivery of enzyme secreted from transduced cells to somatic tissues via the peripheral circulation corrected most somatic pathology. However, unlike an earlier study, central nervous system (CNS) pathology remained unchanged. Conversely, intraventricular gene delivery resulted in widespread sulphamidase gene delivery in (and reduced lysosomal storage throughout) the brain. Improvements in behaviour were observed in these mice, and interestingly, pathological urinary retention was prevented.

CONCLUSIONS

The CNS remains the last major barrier to effective therapy for children affected by LSDs. The blood-brain barrier (BBB) limits the uptake of lysosomal enzymes from the peripheral circulation into the CNS, making direct gene delivery to the brain a reasonable, albeit more challenging, therapeutic option. Future work will further assess the relative advantages of directly targeting the brain with somatic gene delivery with sulphamidase modified to increase the efficiency of transport across the BBB.

Trans-generational exposure to low levels of rhodamine B does not adversely affect litter size or liver function in murine mucopolysaccharidosis type IIIA

MPS IIIA is a lysosomal storage disorder caused by mutations in the sulphamidase gene, resulting in the accumulation of heparan sulphate glycosaminoglycans (HS GAGs). Symptoms predominantly manifest in the CNS and there is no current therapy that effectively addresses neuropathology in MPS IIIA patients. Recent studies in MPS IIIA mice have shown that rhodamine B substrate deprivation therapy (SDT) (also termed substrate reduction therapy/SRT) inhibits GAG biosynthesis and, improves both somatic and CNS disease pathology. Acute overexposure to high doses of rhodamine B results in liver toxicity and is detrimental to reproductive ability. However, the long-term effects of decreasing GAG synthesis, at the low dose sufficient to alter neurological function are unknown. A trans-generational study was therefore initiated to evaluate the continuous exposure of rhodamine B treatment in MPS IIIA mice over 4 generations, including treatment during pregnancy. No alterations in litter size, liver histology or liver function were observed. Overall, there are no long-term issues with the administration of rhodamine B at the low dose tested and no adverse effects were noted during pregnancy in mice.