Low bone mass in Pompe disease: muscular strength as a predictor of bone mineral density

Effects of enzyme replacement therapy on bone density in late onset Pompe disease

Pompe disease is an autosomal recessive disorder caused by a deficiency of α-glucosidase, resulting in the accumulation of glycogen in smooth, cardiac, and skeletal muscles, leading to skeletal muscle dysfunction, proximal muscle weakness, and early respiratory insufficiency. Although many patients exhibit decreased bone mineral density (BMD) and increased fractures, there is currently no official protocol for surveillance and management of osteoporosis and osteopenia in late onset Pompe disease (LOPD). Enzyme replacement therapy (ERT) has therapeutic effects on muscle function; however, very few studies report on the effect of ERT on bone mineralization in LOPD patients. Our study included 15 Pompe patients from 25 to 76 years of age on ERT for variable durations. Progressive impact of ERT on BMD of the hips and spine, and the frequency of osteopenia or osteoporosis was studied using DEXA scanning, and correlations were made with age of initiation of ERT, duration of ERT and six-minute walk test. We found a significant positive correlation between the age of ERT initiation and age of the subject, with increases in the Z-scores for the femur and lumbar region. Females had a significantly higher risk for developing osteoporosis compared to males. These results highlight the significance of ERT on reducing progression of osteoporosis in LOPD patients.

Long-term benefits of physical activity in adult patients with late onset Pompe disease: a retrospective cohort study with 10 years of follow-up

BACKGROUND

In 2011 a 12 weeks personalized exercise training program in 23 mildly affected adult late onset Pompe patients (age 19.6-70.5 years) improved endurance, muscle strength and function. Data on long-term effects of this program or of other physical activity in Pompe disease are absent. This retrospective cohort study aimed to explore effects of long-term healthy physical activity according to the WHO norm and the former exercise training program on the disease course.

RESULTS

A total of 29 adult late onset Pompe patients were included: 19 former exercise training program participants and 10 comparable control patients. Patients, who based on interviews, met the 2010 WHO healthy physical activity norm (active, n = 16) performed better on endurance (maximal cardiopulmonary exercise test), muscle strength and function compared to patients not meeting this norm (inactive, n = 13) (p < 0.05). Majority of the outcomes, including endurance and manually tested muscle strength, tended to be higher in the active patients of the 2011 training cohort who continued the program compared to active control patients (p > 0.05).

CONCLUSION

In Pompe disease long-term healthy physical activity according to the 2010 WHO norm leads to physical benefits and a personalized exercise training program may have additional favorable effects and both should be recommended as standard of care.

Evaluation of bone health in patients with mucopolysaccharidosis

INTRODUCTION

This study aimed to evaluate the relationship between clinical findings, height and weight standard deviation scores, 25-hydroxyvitamin D₃ (25(OH)D₃) level, and dual-energy X-ray absorptiometry (DXA) results in patients diagnosed with mucopolysaccharidosis (MPS), where effective current treatments such as enzyme replacement therapy (ERT) can be accessed.

MATERIALS AND METHODS

25(OH)D₃ level was measured in 126 patients with MPS (17 with MPS I, 14 with MPS II, 18 with MPS III, 33 with MPS IVA, and 44 with MPS VI; 24-524 months). DXA was performed in 45 of these patients (8 with MPS I, 4 with MPS II, 4 with MPS III, 12 with MPS IVA, and 17 with MPS VI; 62-197 months; all patients were under 18 when DXA was performed) to assess bone mineral density (BMD) of the lumbar spine.

RESULTS

In total, 67.5% patients had a short stature, and 50% of them were underweight for their age. Of the patients, 13.5% were immobile, 28.6% had 25(OH)D₃ deficiency, and 30.2% had an insufficient level of 25(OH)D₃. BMD z score of 45 patients was - 2.5 ± 1.7. In 40% patients, it was <  - 2. However, after correction for height-for-age z score (HAZ), HAZ-adjusted BMD z score was - 0.1 ± 0.9. In 2.2% patients, it was <  - 2.

CONCLUSION

The low BMD z score prevalence reported with DXA was misleadingly higher in children with MPS and short stature. To prevent exposure to unnecessary antiresorptive treatments in these children, the effect of severe short stature and bone geometry on DXA measurements should be considered; further studies on bone health are warranted.

A retrospective longitudinal study and comprehensive review of adult patients with glycogen storage disease type III

INTRODUCTION

A deficiency of glycogen debrancher enzyme in patients with glycogen storage disease type III (GSD III) manifests with hepatic, cardiac, and muscle involvement in the most common subtype (type a), or with only hepatic involvement in patients with GSD IIIb.

OBJECTIVE AND METHODS

To describe longitudinal biochemical, radiological, muscle strength and ambulation, liver histopathological findings, and clinical outcomes in adults (≥18 years) with glycogen storage disease type III, by a retrospective review of medical records.

RESULTS

Twenty-one adults with GSD IIIa (14 F & 7 M) and four with GSD IIIb (1 F & 3 M) were included in this natural history study. At the most recent visit, the median (range) age and follow-up time were 36 (19-68) and 16 years (0-41), respectively. For the entire cohort: 40% had documented hypoglycemic episodes in adulthood; hepatomegaly and cirrhosis were the most common radiological findings; and 28% developed decompensated liver disease and portal hypertension, the latter being more prevalent in older patients. In the GSD IIIa group, muscle weakness was a major feature, noted in 89% of the GSD IIIa cohort, a third of whom depended on a wheelchair or an assistive walking device. Older individuals tended to show more severe muscle weakness and mobility limitations, compared with younger adults. Asymptomatic left ventricular hypertrophy (LVH) was the most common cardiac manifestation, present in 43%. Symptomatic cardiomyopathy and reduced ejection fraction was evident in 10%. Finally, a urinary biomarker of glycogen storage (Glc4) was significantly associated with AST, ALT and CK.

CONCLUSION

GSD III is a multisystem disorder in which a multidisciplinary approach with regular clinical, biochemical, radiological and functional (physical therapy assessment) follow-up is required. Despite dietary modification, hepatic and myopathic disease progression is evident in adults, with muscle weakness as the major cause of morbidity. Consequently, definitive therapies that address the underlying cause of the disease to correct both liver and muscle are needed.

Recommendations for Infantile-Onset and Late-Onset Pompe Disease: An Iranian Consensus

Background: Pompe disease, also denoted as acid maltase or acid α-glucosidase deficiency or glycogen storage disease type II, is a rare, autosomal recessive lysosomal storage disorder. Several reports have previously described Pompe disease in Iran and considering increased awareness of related subspecialties and physicians, the disease's diagnosis is growing.

Objective: This guideline's main objective was to develop a national guideline for Pompe disease based on national and international evidence adapting with national necessities.

Methods: A group of expert clinicians with particular interests and experience in diagnosing and managing Pompe disease participated in developing this guideline. This group included adult neurologists, pediatric neurologists, pulmonologists, endocrinologists, cardiologists, pathologists, and physiatrists. After developing search terms, four authors performed an extensive literature review, including Embase, PubMed, and Google Scholar, from 1932 to current publications before the main meeting. Before the main consensus session, each panel member prepared an initial draft according to pertinent data in diagnosis and management and was presented in the panel discussion. Primary algorithms for the diagnosis and management of patients were prepared in the panel discussion. The prepared consensus was finalized after agreement and concordance between the panel members.

Conclusion: Herein, we attempted to develop a consensus based on Iran's local requirements. The authors hope that disseminating these consensuses will help healthcare professionals in Iran achieve the diagnosis, suitable treatment, and better follow-up of patients with infantile-onset Pompe disease and late-onset Pompe disease.

Association between handgrip strength and bone mass parameters in HIV-infected children and adolescents. A cross-sectional study

BACKGROUND

Low bone mineral content (BMC) and bone mineral density (BMD) have been identified in human immunodeficiency virus (HIV)-infected children and adolescents. The direct adverse effects of HIV infection and combined antiretroviral therapy (ART) negatively contribute to bone metabolism. A direct relationship between muscle strength levels and BMD in HIV-infected adults and older adults has been described. However, it is unknown whether handgrip strength (HGS) is associated with bone mass in pediatric populations diagnosed with HIV.

OBJECTIVE

To ascertain whether HGS levels are associated with BMC and BMD in HIV-infected children and adolescents.

DESIGN AND SETTING

Cross-sectional study conducted in Florianãpolis, Brazil, in 2016.

METHODS

The subjects were 65 children and adolescents (8-15 years) diagnosed with vertically-transmitted HIV. Subtotal and lumbar-spine BMC and BMD were obtained via dual-emission X-ray absorptiometry (DXA). HGS was measured using manual dynamometers. The covariates of sex, ART, CD4+ T lymphocytes and viral load were obtained through questionnaires and medical records. Sexual maturation was self-reported and physical activity was measured using accelerometers. Simple and multiple linear regression were used, with P < 0.05.

RESULTS

HGS was directly associated with subtotal BMD (β = 0.002; R² = 0.670; P < 0.001), subtotal BMC (β = 0.090; R² = 0.734; P = 0.005) and lumbar-spine BMC (β = 1.004; R² = 0.656; P = 0.010) in the adjusted analyses. However, no significant association was found between HGS and lumbar-spine BMD (β = 0.001; R² = 0.464; P = 0.299).

CONCLUSION

HGS was directly associated with BMD and BMC in HIV-infected children and adolescents.

Rare Variants in Autophagy and Non-Autophagy Genes in Late-Onset Pompe Disease: Suggestions of Their Disease-Modifying Role in Two Italian Families

Pompe disease is an autosomal recessive disorder caused by a deficiency in the enzyme acid alpha-glucosidase. The late-onset form of Pompe disease (LOPD) is characterized by a slowly progressing proximal muscle weakness, often involving respiratory muscles. In LOPD, the levels of GAA enzyme activity and the severity of the clinical pictures may be highly variable among individuals, even in those who harbour the same combination of GAA mutations. The result is an unpredictable genotype–phenotype correlation. The purpose of this study was to identify the genetic factors responsible for the progression, severity and drug response in LOPD. We report here on a detailed clinical, morphological and genetic study, including a whole exome sequencing (WES) analysis of 11 adult LOPD siblings belonging to two Italian families carrying compound heterozygous GAA mutations. We disclosed a heterogeneous pattern of myopathic impairment, associated, among others, with cardiac defects, intracranial vessels abnormality, osteoporosis, vitamin D deficiency, obesity and adverse response to enzyme replacement therapy (ERT). We identified deleterious variants in the genes involved in autophagy, immunity and bone metabolism, which contributed to the severity of the clinical symptoms observed in the LOPD patients. This study emphasizes the multisystem nature of LOPD and highlights the polygenic nature of the complex phenotype disclosed in these patients.

Nutrition in adult patients with selected lysosomal storage diseases

Lysosomal storage disorders (LSDs) are a group of clinically heterogeneous disorders affecting the function of lysosomes and are characterized by an accumulation of undigested substrates within several cell types. In recent years there have been substantial advances in supportive care and drug treatment for some LSDs, leading to improved patient survival, as seen in Gaucher, Pompe and Fabry disease and some Mucopolysaccharidoses; however, many symptoms still persist. Thus it is now even more important to improve patients' quality of life and reduce symptoms and comorbidities. One potential way of achieving this goal is through adjunct nutritional therapy, which is challenging as patients may be overweight with associated consequences, or malnourished, or underweight. Furthermore, drugs used to treat LSDs can modify the metabolic status and needs of patients. There are currently not enough data to make specific dietary recommendations for individual LSDs; however, suggestions can be made for managing clinical manifestations of the diseases, as well as treatment-associated adverse events. The metabolic and nutritional status of adult patients must be regularly assessed and individualized dietary plans may be created to cater to a patient's specific needs. Damage to the autophagic process is a common feature in LSDs that is potentially sensitive to dietary manipulation and needs to be assessed in clinical studies.

Body composition and 6 minute walking ability in late-onset pompe disease patients after 9 years of enzyme replacement therapy

OBJECTIVE

Pompe disease is a rare autosomal recessive disorder caused by the deficiency of acid α-glycosidase resulting in accumulation of glycogen in the lysosomes. The late-onset form of the disease (LOPD) causes primarily progressive muscle weakness and respiratory insufficiency. Enzyme replacement therapy (ERT) introduced in 2006, showed mild improvement or stabilization of the symptoms although long-term data are limited. Aim of the study was to describe the progression of body composition and walking ability in LOPD patients receiving ERT consistently for 9 years.

METHODS

Lean body mass, bone mineral density, body fat and 6 min walking distance were assessed in three male and three female LOPD patients (height 165.8 ± 11.2 cm, age 42.3 ± 11.8yrs, body mass 71.1 ± 20.8 kg, at study entry), every three years, for 9 years since ERT initiation (T0, T3, T6, T9).

RESULTS

Total body and upper extremities' lean mass remained unchanged (p < 0.05), but it was decreased for the lower extremities (T3:13.06 ± 3.848 kg vs. T9:11.63 ± 3.49 kg, p < 0.05). Lean body mass was not significantly different after 9 years of ERT compared to before the ERT initiation (T0 to T9). Bone mineral density remained unchanged. Percent body fat increased (T0:39.1 ± 10.3%, vs. T9:43.1 ± 10.4%, p < 0.05). Six minute walking distance tended to increase after 3 years of ERT and decreased gradually thereafter, with no difference between T0-T9. Lean mass of the lower extremities adjusted for body weight was significantly correlated with 6 min walking distance (r = 0.712, p < 0.05).

CONCLUSION

The current data show that enzyme replacement therapy may preserve lean body mass, bone mineral density and walking capacity in LOPD patients.

Myostatin Inhibitors: Panacea or Predicament for Musculoskeletal Disorders?

Myostatin, also known as growth differentiation factor 8 (GDF8), is a transforming growth factor-β (TGF-β) family member that functions to limit skeletal muscle growth. Accordingly, loss-of-function mutations in myostatin result in a dramatic increase in muscle mass in humans and various animals, while its overexpression leads to severe muscle atrophy. Myostatin also exerts a significant effect on bone metabolism, as demonstrated by enhanced bone mineral density and bone regeneration in myostatin null mice. The identification of myostatin as a negative regulator of muscle and bone mass has sparked an enormous interest in developing myostatin inhibitors as therapeutic agents for treating a variety of clinical conditions associated with musculoskeletal disorders. As a result, various myostatin-targeting strategies involving antibodies, myostatin propeptides, soluble receptors, and endogenous antagonists have been generated, and many of them have progressed to clinical trials. Importantly, most myostatin inhibitors also repress the activities of other closely related TGF-β family members including GDF11, activins, and bone morphogenetic proteins (BMPs), increasing the potential for unwanted side effects, such as vascular side effects through inhibition of BMP 9/10 and bone weakness induced by follistatin through antagonizing several TGF-β family members. Therefore, a careful distinction between targets that may enhance the efficacy of an agent and those that may cause adverse effects is required with the improvement of the target specificity. In this review, we discuss the current understanding of the endogenous function of myostatin, and provide an overview of clinical trial outcomes from different myostatin inhibitors.

Neuromuscular Diseases and Bone

Neuromuscular diseases (NMDs) are inherited or acquired conditions affecting skeletal muscles, motor nerves, or neuromuscular junctions. Most of them are characterized by a progressive damage of muscle fibers with reduced muscle strength, disability, and poor health-related quality of life of affected patients. In this scenario, skeletal health is usually compromised as a consequence of modified bone-muscle cross-talk including biomechanical and bio-humoral issues, resulting in increased risk of bone fragility and fractures. In addition, NMD patients frequently face nutritional issues, including malnutrition due to feeding disorders and swallowing problems that might affect bone health. Moreover, in these patients, low levels of physical activity or immobility are common and might lead to overweight or obesity that can also interfere with bone strength features. Also, vitamin D deficiency could play a critical role both in the pathogenesis and in the clinical scenario of many NMDs, suggesting that its correction could be useful in maintaining or enhancing bone health, especially in the early phases of NMDs. Last but not least, specific disease-modifying drugs, available for some NMDs, are frequently burdened with adverse effects on bone tissue. For example, glucocorticoid therapy, standard of care for many muscular dystrophies, prolongs long-term survival in treated patients; nevertheless, high dose and/or chronic use of these drugs are a common cause of secondary osteoporosis. This review addresses the current state of knowledge about the factors that play a role in determining bone alterations reported in NMDs, how these factors can modify the biological pathways underlying bone health, and which are the available interventions to manage bone involvement in patients affected by NMDs. Considering the complexity of care of these patients, an interdisciplinary and multimodal management strategy based on both pharmacological and non-pharmacological interventions is recommended, particularly targeting musculoskeletal issues that are closely related to functional independence as well as social implications.

Systematic review of oral and craniofacial findings in patients with Fabry disease or Pompe disease

Fabry disease and Pompe disease are rare lysosomal storage disorders that belong to a heterogeneous group of more than 200 distinct inborn metabolic diseases. Mutations followed by loss of function of enzymes or transporters that are localised in the acidic environment of the lysosome may result in degradation of many substrates, such as glycosaminoglycans, glycosphingolipids, glycogen, cholesterol, oligosaccharides, glycoproteins, and peptides, or the excretion of the products degraded by the lysosome. Our aim was to identify the oral signs and symptoms of Fabry disease and Pompe disease from a systematic review made using MEDLINE/PubMed, and a hand search for relevant articles, following the PRISMA guidelines. Both diseases show various craniofacial and oral changes, including supernumerary teeth, dental agenesis, angiokeratoma, and telangiectases in Fabry disease; and macroglossia, teeth fusion, and taurodontism in Pompe disease. Common clinical signs of Fabry disease include hyposalivation, hypohidrosis, and xerophthalmia, and a generally reduced physical resilience was apparent in patients with Pompe disease. Oral and craniofacial changes in patients with both diseases extend over their entire lifetime and can be detected even in an infant. Lysosomal storage diseases should be taken into consideration in the differential diagnosis of relevant diverse symptoms, because treatment, when available, is most effective when started early. The main therapeutic concepts are enzymatic replacement for Pompe disease, whereas patients with Fabry disease require additional oral chaperone treatment or enzyme replacement.

Multisystem late onset Pompe disease (LOPD): an update on clinical aspects

Pompe disease is classified by age of onset, organ involvement, severity, and rate of progression in two main forms: the first one, infantile onset Pompe disease (IOPD), presents before the age of 12 months with generalized muscle weakness, hypotonia, respiratory distress, and hypertrophic cardiomyopathy as main clinical features. The second form, late onset Pompe disease (LOPD), is characterized by an onset at the age of 12 months to adulthood, hyperCKemia, and limb-girdle and axial muscle weakness, often complicated by respiratory muscles degeneration. In the last 10-15 years, an increasing interest in Pompe disease has led to multiple studies in an effort to clarify the emerging clinical aspects, to find out the best diagnostic tools to identify the disease as early as possible, and to offer new therapeutic options apart from enzyme replacement therapy (ERT). Since 2006, ERT-the first treatment for Pompe disease-has been universally accepted in the majority of countries all over the world. Although for years Pompe disease has been primarily considered a muscle disorder, nowadays it is clear that the involvement of several other organs has changed the cultural approach to this entity which is now viewed as a multisystem disorder. The emerging clinical aspects have greatly expanded the spectrum of the disease manifestations. In fact, central, peripheral, and autonomous nervous systems are often involved; vascular malformations and heart involvement are frequently observed; musculoskeletal and bone changes as well as oro-gastrointestinal and urinary tract alterations have been better defined. A great deal of effort has been made to clarify the clinical aspects of Pompe disease, to raise awareness of the LOPD patients' problems and to improve their quality of life.

Nutrition and exercise in Pompe disease

The current standard of care for Pompe disease (PD) is the administration of enzyme replacement therapy (ERT). Exercise and nutrition are often considered as complementary strategies rather than "treatments" per se. Nutritional assessment is important in patients with locomotor disability because the relative hypodynamia limits energy expenditure and thus the total amount of energy must be reduced to avoid obesity. A lower total energy intake often leads to lower protein and micronutrient intake. Consequently, ensuring that Pompe patients are tested for and replaced for deficiencies (protein, vitamin D, vitamin B12, etc.) is an important aspect of care. Furthermore, given the role of autophagy in the pathophysiology of PD and the fact that fasting induces autophagy, it is important that strategies such as nutritional timing and amino acid intake (L-arginine, L-leucine) be evaluated as therapies. Exercise interventions have been shown to improve six-minute walk testing distance by more than what was seen in the seminal ERT study in late-onset PD. Exercise therapy can also activate autophagy, and this is likely another component of its efficacy. The current review will evaluate the theoretical and practical aspects of nutrition and exercise as therapies for patients with PD.

Rehabilitation management of Pompe disease, from childhood trough adulthood: A systematic review of the literature

Pompe disease (PD) is a rare neuromuscular disorder caused by a deficiency of the enzyme acid alpha-glucosidase. There are three forms of PD depending on the age at onset and clinical severity. PD causes involvement of different organ systems, such as the heart, musculoskeletal system, and respiratory system. As of today, enzyme replacement therapy represents the main therapeutic tool for PD. Rehabilitation is an integral part of a multidisciplinary approach to this pathology. The goal of the present review is to find scientific evidence for the rehabilitative approach to PD, with respect to both the infantile- and adult-onset forms. A systematic literature review was made using the following databases: Pubmed, Pedro, Cochrane Library, EDS Base Index, Trip, and Cinhal. Randomized controlled trials or cohort studies with a sample population of at least six subjects were retrieved. The PICO method was used to formulate the clinical query. The search resulted in 1665 articles. Of these, four cohort studies were subjected to the final phase of the review. Three studies regarded inspiratory muscle training with a threshold, while the fourth study analyzed the effectiveness of therapeutic, aerobic, and reinforcement exercises. Inspiratory muscle training with a threshold increases the pressures generated during inhalation. Aerobic exercise is capable of increasing patients' muscular endurance and performance. To date, however, rehabilitative treatment for patients with PD has no validation in evidencebased medicine. Further studies, possibly with a larger sample size and higher quality are necessary to confirm the effectiveness of rehabilitation in patients with PD.

Elevated Creatine Kinase in a 6-Year-Old Boy

Paucisymptomatic or asymptomatic but persistently elevated serum creatine kinase is not an uncommon pediatric neurology referral question. The challenge is in promptly identifying etiologies with specific treatments, even if they are rare. The presenting features for a child or adolescent with juvenile-onset Pompe disease (JOPD) can be nonspecific and heterogeneous. Clinical manifestations can appear at any age after 2 years and before adulthood, with insidious onset of symptoms related to slowly progressive skeletal or respiratory muscle weakness. This reported case highlights the importance of screening for JOPD in children with "hyper-CK-emia." Dried blood spot measuring acid α-glucosidase enzyme activity is reliable, rapid, noninvasive, and inexpensive, allowing early diagnosis. Diagnosis of JOPD is important as enzyme replacement therapy with alglucosidase alpha, an intravenous recombinant α-glucosidase, is available, and early treatment improves muscle function, quality of life, and long-term survival.

A New Condition in McArdle Disease: Poor Bone Health-Benefits of an Active Lifestyle

INTRODUCTION-PURPOSE

McArdle disease (muscle glycogen phosphorylase deficiency) is a genetic condition associated with exercise intolerance, but how it affects lean mass (LM) and bone mineral content (BMC) and density (BMD) in patients is unknown. We compared these variables between McArdle patients and age-/sex-matched healthy controls and assessed their potential association with physical activity levels in patients.

METHODS

A case-control, cross-sectional design was used to examine LM, BMC, and BMD by using dual-energy x-ray absorptiometry in 136 young adults of both sexes (36 McArdle patients (33 ± 15 yr) and 103 controls (34 ± 11 yr)). Physical activity was assessed using the International Physical Activity Questionnaire.

RESULTS

McArdle patients had significantly lower LM values in whole-body and regional sites compared with their corresponding controls, whereas no differences were found (except for the trunk) when physically active patients (n = 23) were compared with controls. All bone-related variables were significantly lower in patients than in controls (average difference of 13% for BMC and 7.6% for BMD). By contrast, no significant differences at the lumbar spine, pelvis, and femur sites were found between physically active patients and controls.

CONCLUSIONS

We report on a previously undescribed condition in McArdle patients, poor bone health, which warrants further attention because it can occur in relatively young adults. An active lifestyle can at least partly alleviate this disorder presumably because of its beneficial effect on LM.

Bone health in patients with inborn errors of metabolism

Inborn errors of metabolism encompass a wide spectrum of disorders, frequently affecting bone. The most important metabolic disorders that primarily influence calcium or phosphate balance, resulting in skeletal pathology, are hypophosphatemic rickets and hypophosphatasia. Conditions involving bone marrow or affecting skeletal growth and development are mainly the lysosomal storage disorders, in particular the mucopolysaccharidoses. In these disorders skeletal abnormalities are often the presenting symptom and early recognition and intervention improves outcome in many of these diseases. Many disorders of intermediary metabolism may impact bone health as well, resulting in higher frequencies of osteopenia and osteoporosis. In these conditions factors contributing to the reduced bone mineralization can be the disorder itself, the strict dietary treatment, reduced physical activity or sunlight exposure and/or early ovarian failure. Awareness of these primary or secondary bone problems amongst physicians treating patients with inborn errors of metabolism is of importance for optimization bone health and recognition of skeletal complications.

Mitochondrial Point Mutation m.3243A>G Associates With Lower Bone Mineral Density, Thinner Cortices, and Reduced Bone Strength: A Case-Control Study

Mitochondrial dysfunction is associated with several clinical manifestations including diabetes mellitus (DM), neurological disorders, renal and hepatic diseases, and myopathy. Although mitochondrial dysfunction is associated with increased bone resorption and decreased bone formation in mouse models, effects of alterations in mitochondrial function on bone remodeling and mass have not been investigated in humans. We recruited 45 carriers (29 females, 16 males) with the m.3243A>G mutation and healthy controls matched for gender, age, height, and menopausal status. DXA and HRpQCT scans were performed, and bone turnover markers (BTMs) P1NP and CTX were measured. Cases and controls were well matched except for body weight, which was lower in cases (63.6 ± 18.1 kg versus 74.6 ± 14.8 kg, p < 0.01), and manifest DM was present in 25 of 45 cases (none in controls). Bone scans showed lower BMD at the lumbar spine, total hip, and femoral neck in cases. Mean lumbar spine, total hip, and femoral neck T-scores were -1.5, -1.3, and -1.6 in cases, respectively, and -0.8, -0.3, and -0.7 in controls (all p < 0.05). The m.3243A>G mutation was associated with lower BMD, cortical but not trabecular density, cortical thickness, and estimated bone strength. Furthermore, BTMs were lower in the m.3243A>G group before but not after adjustment for DM. The mitochondrial point mutation m.3243A>G was associated with decreased bone mass and strength. Although the coexistence of DM may have influenced bone turnover, the bone phenotype observed in m.3243A>G cases appeared to mirror age-related deterioration in bone, suggesting that mitochondrial dysfunction may cause a premature aging of bone. © 2017 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Improvement of bone mineral density after enzyme replacement therapy in Chinese late-onset Pompe disease patients

Objective

Late-onset Pompe disease (LOPD) is a lysosomal storage disease resulted from deficiency of the enzyme acid α-glucosidase. Patients usually develop a limb-girdle pattern of myopathy and respiratory impairment, and enzyme replacement therapy (ERT) is the only specific treatment available. Recently, LOPD has been associated with low bone mineral density (BMD), but the effect of ERT on BMD is inconclusive. In this report we described our early observations on the change of BMD after ERT in Chinese LOPD patients.

Results

We studied four Chinese LOPD patients with different severities of myopathy. All were underweight, and three had osteoporosis at baseline. We found significant weight gain in three patients after ERT and all four patients showed improvement in BMD. The biggest improvement, 84.4% increase in BMD, was seen in a lady with the most prominent weight recovery. Our results suggest that ERT improves BMD in Chinese LOPD and weight gain could be a major contributor to this effect.

Activin receptor type 2A (ACVR2A) functions directly in osteoblasts as a negative regulator of bone mass

Bone and skeletal muscle mass are highly correlated in mammals, suggesting the existence of common anabolic signaling networks that coordinate the development of these two anatomically adjacent tissues. The activin signaling pathway is an attractive candidate to fulfill such a role. Here, we generated mice with conditional deletion of activin receptor (ACVR) type 2A, ACVR2B, or both, in osteoblasts, to determine the contribution of activin receptor signaling in regulating bone mass. Immunohistochemistry localized ACVR2A and ACVR2B to osteoblasts and osteocytes. Primary osteoblasts expressed activin signaling components, including ACVR2A, ACVR2B, and ACVR1B (ALK4) and demonstrated increased levels of phosphorylated Smad2/3 upon exposure to activin ligands. Osteoblasts lacking ACVR2B did not show significant changes in vitro However, osteoblasts deficient in ACVR2A exhibited enhanced differentiation indicated by alkaline phosphatase activity, mineral deposition, and transcriptional expression of osterix, osteocalcin, and dentin matrix acidic phosphoprotein 1. To investigate activin signaling in osteoblasts in vivo, we analyzed the skeletal phenotypes of mice lacking these receptors in osteoblasts and osteocytes (osteocalcin-Cre). Similar to the lack of effect in vitro, ACVR2B-deficient mice demonstrated no significant change in any bone parameter. By contrast, mice lacking ACVR2A had significantly increased femoral trabecular bone volume at 6 weeks of age. Moreover, mutant mice lacking both ACVR2A and ACVR2B demonstrated sustained increases in trabecular bone volume, similar to those in ACVR2A single mutants, at 6 and 12 weeks of age. Taken together, these results indicate that activin receptor signaling, predominantly through ACVR2A, directly and negatively regulates bone mass in osteoblasts.

Bone mineral density in patients with mucopolysaccharidosis type III

Mucopolysaccharidosis type III (MPS III) is a neurodegenerative disorder. In MPS III patients, heparan sulfate accumulates in many tissues especially the central nervous system. There are limited data regarding bone involvement in MPS III compared to other MPS types. The aim of this study was to evaluate bone mineral density (BMD) and the prevalence of low bone mass, and to explore the association between BMD, vitamin D levels, bone fracture, and patient characteristics in MPS III. A clinical assessment and interview was held to obtain data about family history, height, weight, body mass index (BMI), nutrition, walking capacity, bone fracture, epilepsy, and medical therapy of 15 patients with MPS III. Height, weight, and BMI z scores were calculated. Laboratory tests including 25-hydroxyvitamin D (25-OH-D) were measured. BMD measurements for the lumbar spine were obtained using dual-energy X-ray absorptiometry (DXA). BMD z scores were adjusted for height-for-age z score (HAZ) to provide correction for height deficits. Lumbar spine BMD z score was low (<-1) in five patients for chronological age and normalized in two of five patients after adjustment for HAZ. Three patients continued to have low BMD; these were older than the other patients and one had a history of long bone fracture. Two of these patients were observed to have lost walking capacity at 10 and 14 years, and the other was walking with support. Six patients had deficient, and three patients had insufficient levels of 25-OH-D. Two osteoporotic patients had significantly lower levels of 25-OH-D. We found that older patients with immobility are at high risk of osteoporosis and bone fracture, and vitamin D deficiencies/insufficiencies are widely seen. We recommend monitoring BMD by DXA and checking vitamin D metabolism to assess low bone mass and fracture risk in older MPS III patients with immobility.

The emerging phenotype of late-onset Pompe disease: A systematic literature review

BACKGROUND

Pompe disease is an autosomal recessive disorder caused by deficiency of the lysosomal glycogen-hydrolyzing enzyme acid α-glucosidase (GAA). The adult-onset form, late-onset Pompe disease (LOPD), has been characterized by glycogen accumulation primarily in skeletal, cardiac, and smooth muscles, causing weakness of the proximal limb girdle and respiratory muscles. However, increased scientific study of LOPD continues to enhance understanding of an evolving phenotype.

PURPOSE

To expand our understanding of the evolving phenotype of LOPD since the approval of enzyme replacement therapy (ERT) with alglucosidase alfa (Myozyme™/Lumizyme™) in 2006.

METHODS

All articles were included in the review that provided data on the charactertistics of LOPD identified via the PubMed database published since the approval of ERT in 2006. All signs and symptoms of the disease that were reported in the literature were identified and included in the review.

RESULTS

We provide a comprehensive review of the evolving phenotype of LOPD. Our findings support and extend the knowledge of the multisystemic nature of the disease.

CONCLUSIONS

With the advent of ERT and the concurrent increase in the scientific study of LOPD, the condition once primarily conceptualized as a limb-girdle muscle disease with prominent respiratory involvement is increasingly recognized to be a condition that results in signs and symptoms across body systems and structures.

Pompe Disease: Diagnosis and Management. Evidence-Based Guidelines from a Canadian Expert Panel

Pompe disease is a lysosomal storage disorder caused by a deficiency of the enzyme acid alpha-glucosidase. Patients have skeletal muscle and respiratory weakness with or without cardiomyopathy. The objective of our review was to systematically evaluate the quality of evidence from the literature to formulate evidence-based guidelines for the diagnosis and management of patients with Pompe disease. The literature review was conducted using published literature, clinical trials, cohort studies and systematic reviews. Cardinal treatment decisions produced seven management guidelines and were assigned a GRADE classification based on the quality of evidence in the published literature. In addition, six recommendations were made based on best clinical practices but with insufficient data to form a guideline. Studying outcomes in rare diseases is challenging due to the small number of patients, but this is in particular the reason why we believe that informed treatment decisions need to consider the quality of the evidence.

Diagnosis and treatment of late-onset Pompe disease in the Middle East and North Africa region: consensus recommendations from an expert group

Background

Pompe disease is a rare autosomal recessive disorder caused by a deficiency of the lysosomal enzyme alpha-glucosidase responsible for degrading glycogen. Late-onset Pompe disease has a complex multisystem phenotype characterized by a range of symptoms.

Methods

An expert panel from the Middle East and North Africa (MENA) region met to create consensus-based guidelines for the diagnosis and treatment of late-onset Pompe disease for the MENA region, where the relative prevalence of Pompe disease is thought to be high but there is a lack of awareness and diagnostic facilities.

Results

These guidelines set out practical recommendations and include algorithms for the diagnosis and treatment of late-onset Pompe disease. They detail the ideal diagnostic workup, indicate the patients in whom enzyme replacement therapy should be initiated, and provide guidance on appropriate patient monitoring.

Conclusions

These guidelines will serve to increase awareness of the condition, optimize patient diagnosis and treatment, reduce disease burden, and improve patient outcomes.

Safety and efficacy of exercise training in adults with Pompe disease: evalution of endurance, muscle strength and core stability before and after a 12 week training program

BACKGROUND

Pompe disease is a proximal myopathy. We investigated whether exercise training is a safe and useful adjuvant therapy for adult Pompe patients, receiving enzyme replacement therapy.

METHODS

Training comprised 36 sessions of standardized aerobic, resistance and core stability exercises over 12 weeks. Before and after, the primary outcome measures safety, endurance (aerobic exercise capacity and distance walked on the 6 min walk test) and muscle strength, and secondary outcome measures core stability, muscle function and body composition, were evaluated.

RESULTS

Of 25 patients enrolled, 23 successfully completed the training. Improvements in endurance were shown by increases in maximum workload capacity (110 W before to 122 W after training, [95 % CI of the difference 6 · 0 to 19 · 7]), maximal oxygen uptake capacity (69 · 4 % and 75 · 9 % of normal, [2 · 5 to 10 · 4]), and maximum walking distance (6 min walk test: 492 meters and 508, [-4 · 4 to 27 · 7] ). There were increases in muscle strength of the hip flexors (156 · 4 N to 180 · 7 N [1 · 6 to 13 · 6) and shoulder abductors (143 · 1 N to 150 · 7 N [13 · 2 to 35 · 2]). As an important finding in secondary outcome measures the number of patients who were able to perform the core stability exercises rose, as did the core stability balancing time (p < 0.05, for all four exercises). Functional tests showed small reductions in the time needed to climb four steps (2 · 4 sec to 2 · 1, [- 0 · 54 to -0 · 04 ]) and rise to standing position (5 · 8 sec to 4 · 8, [-2 · 0 to 0 · 0]), while time to run, the quick motor function test results and body composition remained unchanged.

CONCLUSIONS

Our study shows that a combination of aerobic, strength and core stability exercises is feasible, safe and beneficial to adults with Pompe disease.

Effectiveness of enzyme replacement therapy in adults with late-onset Pompe disease: results from the NCS-LSD cohort study

OBJECTIVES

To determine the effectiveness of enzyme replacement therapy (ERT) for adults with late-onset Pompe disease.

DESIGN

A longitudinal cohort study including prospective and retrospective clinical outcome data. Age- and gender-adjusted treatment effects were estimated using generalised linear mixed models. Treated patients contributed data before and during treatment. Untreated patients contributed natural history data.

PARTICIPANTS

Consenting adults (N = 62) with a diagnosis of late-onset Pompe disease who attended a specialist treatment centre in England. This cohort represented 83 % of all patients in the UK with a confirmed diagnosis of this rare condition. At study entry, all but three patients were receiving ERT (range of treatment duration, 0 to 3.1 years).

OUTCOME MEASURES

Percent predicted forced vital capacity (%FVC); ventilation dependency; mobility; 6 min walk test (6MWT); muscle strength and body mass index (BMI).

RESULTS

An association was found between time on ERT and significant increases in the distance walked in the 6MWT (p < 0.001) and muscle strength scores (p < 0.001). Improvements in both these measures were seen over the first 2 years of treatment with ERT. No statistically significant relationship was found between time on ERT and respiratory function or in BMI.

CONCLUSIONS

These data provide some further evidence of the effectiveness of ERT in adults with late-onset Pompe disease.

SYNOPSIS

The results of this longitudinal cohort study of 62 adults with late-onset Pompe disease, provide further evidence on the effectiveness of ERT in this rare condition.

Risk factors for osteoporosis, falls and fractures in hereditary myopathies and sporadic inclusion body myositis - A cross sectional survey

Background

The risk of osteoporosis is known in myopathies requiring long-term steroid treatment and Pompe disease, but not in other hereditary myopathies or sporadic inclusion body myositis (sIBM).

Methods

Risk factors of osteoporosis, laboratory parameters of bone metabolism, frequency of falls and fractures, walking ability, and pain were surveyed using questionnaires in 89 patients with sIBM and genetically confirmed myopathies facioscapulohumeral muscular dystrophy (FSHD), myotonic dystrophy types 1 and 2 (DM1, DM2), limb girdle muscular dystrophies (LGMD2A, LGMD2B, LGMD2I), MATR3 myopathy, and oculopharyngeal muscular dystrophy (OPMD). Additionally laboratory parameters of bone metabolism were determined.

Results

The mean age at examination per disease group ranged from 32 years in LGMD2A to 70 years in sIBM. Myopathies with a higher degree of walking impairment had a higher risk of falls (sIBM, LGMD2A, LGMD2B). At the time of examination 3.4% had a history of osteoporosis. The 25-OH D3 level was decreased in 20% of patients (and in 55% of patients with LGMDs), 57% of them were ambulatory. The 25-OH D3 level was significantly lower in patients with myopathies than in other neurological disorders (p < 0.001). 2.7 falls per year per person occurred. Fractures were reported in 6.8% of patients within the last year. They involved frequently the tibia bone. The pain score didn't correlate with either the walking disability (WGMS) score or the 25-OH D3 level.

Conclusion

The risk for osteoporosis and reduced 25-OH D3 level seems to be increased in wheelchair-bound patients with myopathy but also in patients with DM1 and autosomal-recessive myopathies.

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Risk factors for osteoporosis and fractures were analysed in hereditary myopathies.

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Wheelchair-bound patients - high risk for osteoporosis and fractures of tibia bone.

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Myopathy patients have lower vitamin D3 levels than controls.

Orthopedic management of patients with Pompe disease: a retrospective case series of 8 patients

INTRODUCTION

Pompe disease (PD), a lysosomal storage disease as well as a neuromuscular disorder, is a rare disease marked by progressive muscle weakness. Enzyme replacement therapy (ERT) in recent years allowed longer survival but brought new problems to the treatment of PD with increasing affection of the musculoskeletal system, particularly with a significantly higher prevalence of scoliosis. The present paper deals with the orthopedic problems in patients with PD and is the first to describe surgical treatment of scoliosis in PD patients.

PATIENTS AND METHODS

The orthopedic problems and treatment of eight patients with PD from orthopedic consultation for neuromuscular disorders are retrospectively presented. We analyzed the problems of scoliosis, hip dysplasia, feet deformities, and contractures and presented the orthopedic treatment options.

RESULTS

Six of our eight PD patients had scoliosis and two young patients were treated by operative spine stabilization with benefits for posture and sitting ability. Hip joint surgery, operative contracture release, and feet deformity correction were performed with benefits for independent activity.

CONCLUSION

Orthopedic management gains importance due to extended survival and musculoskeletal involvement under ERT. Surgical treatment is indicated in distinct cases. Further investigation is required to evidence the effect of surgical spine stabilization in PD.

Improvement of dysphagia in a child affected by Pompe disease treated with enzyme replacement therapy

AIM

Dysphagia is a known complication in Pompe Disease (PD), a severe metabolic myopathy due to alpha-glucosidase deficiency. Enzyme replacement therapy (ERT) with alglucosidase alfa is the only approved therapy for PD. Presently no data are available on the effects of ERT on dysphagia in PD patients. The aim of this work is to evaluate the course of this complication in a 6 years old boy affected by PD after treatment with ERT.

METHODS

Dysphagia was assessed by Videofluoroscopic Swallowing Study (VFSS) at baseline, before the start of ERT and after 36 months of therapy. We used the Dysphagia Severity Rating Scale (DSS) to define the severity grade of dysphagia.

RESULTS

VFSS performed at baseline revealed complete incoordination of oral stage swallowing which was classified as a grade 1 dysphagia according to DSS. After 36 months of treatment VFSS revealed normal swallowing, classified as grade 0 by DSS.

CONCLUSION

Our results suggest that ERT is effective in improving dysphagia. VFSS may be a useful tool to investigate and monitor swallowing disorders in patients affected by PD.

Assessment of bone mineral density by dual energy x-ray absorptiometry in patients with mucopolysaccharidoses

Background

Patients with mucopolysaccharidoses (MPS) are associated with poor bone growth and mineralization, however, information regarding the assessment of bone mineral density (BMD) in relation to age and treatment in this disorder is limited.

Methods

Dual energy x-ray absorptiometry (DXA) was performed in 30 patients with MPS (21 males and 9 females; 2 with MPS I, 12 with MPS II, 2 with MPS IIIB, 9 with MPS IVA, and 5 with MPS VI; median age, 10.8 years; age range, 5.0 years to 23.7 years; 26 patients were under 19 and 4 were above 19 years of age) to assess BMD of the lumbar spine (L1-L4), using the Hologic QDR 4500 system (Bedford, MA, USA).

Results

For 26 patients under 19 years of age, standard deviation scores (z scores) for height, weight, body mass index (BMI), and BMD were −4.53 ± 2.66, -1.15 ± 1.55, 0.74 ± 1.23, and −3.03 ± 1.62, respectively, and they were all negatively correlated with age (p < 0.05). However, after correction for height-for-age z score (HAZ), HAZ adjusted BMD z score was −0.7 ± 1.24. Eight patients (31%) had osteopenia (HAZ adjusted BMD z score < −1 and ≥ −2), and 4 patients (15%) had osteoporosis (HAZ adjusted BMD z score < −2). Of 8 patients with MPS I, II or VI who underwent follow-up DXA after receiving enzyme replacement therapy for 1.0 to 7.4 years, all showed increase in absolute BMD values.

Conclusions

These findings and the follow-up data can be used to develop quality of care strategies for patients with MPS.

Long-term outcomes of children and adolescents who had cerebral palsy with secondary osteoporosis

OBJECTIVE

To investigate the long-term efficacy and index of treatment with vitamin D alone or with a bisphosphonate in children and adolescents who have cerebral palsy (CP) with secondary osteoporosis.

RESEARCH DESIGN AND METHODS

Thirty patients diagnosed with CP and secondary osteoporosis were analyzed for 5 years, and the efficacy of treatment was compared. Treatment was divided into three groups: The monotherapy group, consisting of patients taking only alfacalcidol (0.03 µg/kg/day); the polytherapy group, consisting of those taking alfacalcidol and risedronate (0.05 mg/kg/day); and the control group, consisting of patients who discontinued taking their medications for reasons unrelated to these therapies. Bone mineral density (BMD), bone-specific alkaline phosphate (BAP), and N-telopeptides of type I collagen (NTX/Cr) were measured on each patient just before and at discontinuation of treatment, after 6 months, and again at 1 and 3 years, respectively. The changes in BMD (ΔBMD), BAP (ΔBAP), and NTX/Cr (ΔNTX/Cr) were evaluated at these intervals, because the normal value of each parameter varies over time during childhood.

RESULTS

ΔBMD significantly increased in the polytherapy group at ≥1 year (p = 0.006), and the difference in BMD between the polytherapy and the control groups at ≥1 year was also significant (p = 0.005). ΔBAP was increased in the monotherapy and polytherapy groups at ≥1 year (p = 0.021 and p = 0.033). ΔNTX/Cr decreased in the polytherapy group at ≥1 year, which was consistent with the polytherapy group of the period from 1 month to 1 year (p = 0.033). The relation between ΔBMD to ΔBAP was a positive correlation in the second period in the monotherapy group (r = 0.46). And the relations between ΔBMD to ΔNTX/Cr were not recognized negative correlations in the monotherapy and polytherapy groups. Thus, ΔBMD reflected ossification of secondary osteoporosis in patients with CP, and ΔBAP and ΔNTX/Cr was significantly related to the increase and decrease of ΔBMD. There were no effects of other factors except sexual maturity. Limitations of this study include that each index of examination was the evaluation according to rate of change. Therefore, the results of this study were limited to longitudinal evaluations.

CONCLUSION

Evaluation according to ΔBMD and both methods of monotherapy and polytherapy were useful for CP patient taking antiepileptic drugs (AEDs) and regardless of sex. Especially, polytherapy for longer than 1 year led to improvement in BMD in children who had CP with secondary osteoporosis. BAP and NTX/Cr were useful for the index of the progression osteoporosis with or without these therapies.

Bone density in patients with late onset Pompe disease

BACKGROUND

Pompe disease is an inherited metabolic disorder characterized by α-glycosidase deficiency, which leads to lysosomal glycogen accumulation in many different tissues. The infantile form is the most severe with a rapidly fatal outcome, while the late onset form has a greater phenotypic variability, characterized by skeletal muscle dysfunction and early respiratory involvement. Bone mineral density (BMD) has been recently reported to be reduced in many patients with both forms of the disease. Enzyme replacement therapy (ERT) is now available with an undefined, impact on BMD in patients with late onset disease.

OBJECTIVES

The present study aimed to investigate BMD in patients with late onset form of Pompe disease before and after ERT initiation.

PATIENTS AND METHODS

Dual x-ray absorptiometry (DEXA) was examined in four newly diagnosed patients with late onset Pompe disease and in four adults under ERT before and after ERT initiation with a treatment duration of 18 to 36 months.

RESULTS

The initial DEXA showed normal total body BMD z-score in all the patients, while L2-L4 and femoral neck BMD was reduced in three and two patients, respectively. After ERT administration, two patients had an improvement in L2-L4 lumbar spine and one patient in femoral neck BMD z-score with values within normal range.

CONCLUSIONS

The results suggested that regional BMD may moderately reduce in some patients with the late onset form of Pompe disease, although profound osteopenia was not observed. The improvement of measurements in L2-L4 and femoral neck BMD z-score in some patients with low pre-treatment values after ERT administration needs to be confirmed in larger scale studies.

Consensus treatment recommendations for late-onset Pompe disease

INTRODUCTION

Pompe disease is a rare, autosomal recessive disorder caused by deficiency of the glycogen-degrading lysosomal enzyme acid alpha-glucosidase. Late-onset Pompe disease is a multisystem condition, with a heterogeneous clinical presentation that mimics other neuromuscular disorders.

METHODS

Objective is to propose consensus-based treatment and management recommendations for late-onset Pompe disease.

METHODS

A systematic review of the literature by a panel of specialists with expertise in Pompe disease was undertaken.

CONCLUSIONS

A multidisciplinary team should be involved to properly treat the pulmonary, neuromuscular, orthopedic, and gastrointestinal elements of late-onset Pompe disease. Presymptomatic patients with subtle objective signs of Pompe disease (and patients symptomatic at diagnosis) should begin treatment with enzyme replacement therapy (ERT) immediately; presymptomatic patients without symptoms or signs should be observed without use of ERT. After 1 year of ERT, patients' condition should be reevaluated to determine whether ERT should be continued.

Body composition analysis in late-onset Pompe disease

Pompe disease is an inherited metabolic disorder caused by α-glycosidase deficiency. The adult onset form is mainly characterized by progressive proximal muscle weakness and respiratory dysfunction. The aim of the present study is to evaluate body composition in adult patients before and after enzyme replacement therapy (ERT). Body composition was examined at baseline by means of dual x-ray absorptiometry (DXA) in nine adult patients and after different time periods in six of them who received ERT. Total BMD (bone mineral density) was initially mildly decreased in two patients, while femoral neck BMD was decreased in five patients. On the other hand fat mass was increased in the majority of patients, while body mass index (BMI) was high in four. ERT administration did not seem to induce obvious BMD changes in any patient. Conclusively, the greater femoral neck BMD involvement may be attributed to the lower mechanical load applied by the selectively weakened muscles, whereas the increased fat mass may be the result of metabolic and nutritional derangement.

Therapeutic approaches for lysosomal storage diseases

The lysosomal storage disorders (LSDs) comprise a heterogeneous group of inborn errors of metabolism characterized by tissue substrate deposits, most often caused by a deficiency of the enzyme normally responsible for catabolism of various byproducts of cellular turnover. Individual entities are typified by involvement of multiple body organs, in a pattern reflecting the sites of substrate storage. It is increasingly recognized that one or more processes, such as aberrant inflammation, dysregulation of apoptosis and/or defects of autophagy, may mediate organ dysfunction or failure. Several therapeutic options for various LSDs have been introduced, including hematopoietic stem cell transplantation, enzyme replacement therapy and substrate reduction therapy. Additional strategies are being explored, including the use of pharmacological chaperones and gene therapy. Most LSDs include a variant characterized by primary central nervous system (CNS) involvement. At present, therapy of the CNS manifestations remains a major challenge because of the inability to deliver therapeutic agents across the intact blood-brain barrier. With improved understanding of underlying disease mechanisms, additional therapeutic options may be developed, complemented by various strategies to deliver the therapeutic agent(s) to recalcitrant sites of pathology such as brain, bones and lungs.