The effect of recombinant human iduronate-2-sulfatase (Idursulfase) on growth in young patients with mucopolysaccharidosis type II

Failures of Endochondral Ossification in the Mucopolysaccharidoses

PURPOSE OF REVIEW

The mucopolysaccharidoses (MPS) are a group of inherited lysosomal storage disorders characterized by abnormal accumulation of glycosaminoglycans (GAGs) in cells and tissues. MPS patients frequently exhibit failures of endochondral ossification during postnatal growth leading to skeletal deformity and short stature. In this review, we outline the current understanding of the cellular and molecular mechanisms underlying failures of endochondral ossification in MPS and discuss associated treatment challenges and opportunities.

RECENT FINDINGS

Studies in MPS patients and animal models have demonstrated that skeletal cells and tissues exhibit significantly elevated GAG storage from early in postnatal life and that this is associated with impaired cartilage-to-bone conversion in primary and secondary ossification centers, and growth plate dysfunction. Recent studies have begun to elucidate the underlying cellular and molecular mechanisms, including impaired chondrocyte proliferation and hypertrophy, diminished growth factor signaling, disrupted cell cycle progression, impaired autophagy, and increased cell stress and apoptosis. Current treatments such as hematopoietic stem cell transplantation and enzyme replacement therapy fail to normalize endochondral ossification in MPS. Emerging treatments including gene therapy and small molecule-based approaches hold significant promise in this regard. Failures of endochondral ossification contribute to skeletal deformity and short stature in MPS patients, increasing mortality and reducing quality of life. Early intervention is crucial for effective treatment, and there is a critical need for new approaches that normalize endochondral ossification by directly targeting affected cells and signaling pathways.

Relationships among Height, Weight, Body Mass Index, and Age in Taiwanese Children with Different Types of Mucopolysaccharidoses

Background: Children with mucopolysaccharidosis (MPS) generally appear unaffected at birth but may develop multiple clinical manifestations including profound growth impairment as they grow older. Each type of MPS has a variable age at onset and variable rate of progression, however, information regarding growth in Asian children is limited. Methods: This retrospective analysis included 129 Taiwanese patients with MPS (age range, 0.7 to 19.5 years, median age, 7.9 years) from eight medical centers in Taiwan from January 1996 through December 2018. Results: The mean z scores for the first recorded values of height, weight, and body mass index in the patients’ medical records were −4.25, −1.04, and 0.41 for MPS I (n = 9), −2.31, 0.19, and 0.84 for MPS II (n = 49), −0.42, 0.08, and −0.12 for MPS III (n = 27), −6.02, −2.04, and 0.12 for MPS IVA (n = 30), and −4.46, −1.52, and 0.19 for MPS VI (n = 14), respectively. MPS IVA had the lowest mean z scores for both height and weight among all types of MPS, followed by MPS VI, MPS I, MPS II, and MPS III, which showed the mildest growth retardation. Both z scores for height and weight were negatively correlated with increasing age for all types of MPS (p < 0.01). Of 32 patients younger than 5 years of age, 16 (50%), and 23 (72%) had positive z scores of height and weight, respectively. A substantial number of younger patients with MPS I, II, III, and IVA had a positive height z score. The median age at diagnosis was 3.9 years (n = 115). Conclusions: The patients with MPS IVA had the most significant growth retardation among all types of MPS, followed by MPS VI, MPS I, MPS II, and MPS III. The height and weight of the MPS patients younger than 2–5 years of age were higher than those of healthy individuals, however, their growth significantly decelerated in subsequent years. Understanding the growth curve and potential involved in each type of MPS may allow for early diagnosis and timely management of the disease, which may improve the quality of life.

The importance of anthropological methods in the diagnosis of rare diseases

Most of inborn errors of metabolism (IEMs) and rare endocrine-metabolic diseases (REMD) are rare diseases. According to the European Commission on Public Health, a rare disease is defined, based on its prevalence, as one affecting one in 2000 people. Many IEMs affect body stature, cause craniofacial abnormalities, and disturb the developmental process. Therefore, body proportion, dysmorphic characteristics, and morphological parameters must be assessed and closely monitored. This can be achieved only with the help of an anthropologist who has adequate tools. This is why the role of an anthropologist in collaboration with the physician in the diagnostic process is not to be underestimated. Clinical anthropologists contribute to assessing physical development and improve our understanding of the natural history of rare metabolic diseases. This paper presents anthropometric techniques and methods, such as analysis of demographic data, anthropometric parameters at birth, percentile charts, growth patterns, bioimpedance, somatometric profiles, craniofacial profiles, body proportion indices, and mathematical models of growth curves used in certain rare diseases. Contemporary anthropological methods play an important role in the diagnostic process of rare genetic diseases.

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.

Treatment of mucopolysaccharidosis type II (Hunter syndrome): results from a systematic evidence review

PurposeA pilot systematic evidence review to establish methodology utility in rare genetic diseases, support clinical recommendations, and identify important knowledge gaps.MethodsBroad-based published/gray-literature searches through December 2015 for studies of males with confirmed mucopolysaccharidosis type II (any age, phenotype, genotype, family history) treated with enzyme replacement therapy or hematopoietic stem cell transplantation. Preset inclusion criteria employed for abstract and full document selection, and standardized methods for data extraction and assessment of quality and strength of evidence.ResultsTwelve outcomes reported included benefits of urinary glycosaminoglycan and liver/spleen volume reductions and harms of immunoglobulin G/neutralizing antibody development (moderate strength of evidence). Less clear were benefits of improved 6-minute walk tests, height, early treatment, and harms of other adverse reactions (low strength of evidence). Benefits and harms of other outcomes were unclear (insufficient strength of evidence). Current benefits and harms of hematopoietic stem cell transplantation are unclear, based on dated, low-quality studies. A critical knowledge gap is long-term outcomes. Consensus on selection of critical outcomes and measures is needed to definitively evaluate treatment safety and effectiveness.ConclusionMinor methodology modifications and a focus on critical evidence can reduce review time and resources. Summarized evidence was sufficient to support guidance development and highlight important knowledge gaps.

Growth patterns in children with mucopolysaccharidosis I and II

BACKGROUND

Mucopolysaccharidosis (MPS) diseases lead to a profound disruption in normal mechanisms of growth and development. This study was undertaken to determine the general growth of children with MPS I and II.

METHODS

The anthropometric data of patients with MPS I and II (n=76) were retrospectively analyzed. The growth patterns of these patients were analyzed and then plotted onto Polish reference charts. Longitudinal analyses were performed to estimate age-related changes.

RESULTS

At the time of birth, the body length was greater than reference charts for all MPS groups (Hurler syndrome, P=0.006; attenuated MPS II, P=0.011; severe MPS II, P<0.001). The mean z-score values for every MPS group showed that until the 30th month of life, the growth patterns for all patients were similar. Afterwards, these growth patterns start to differ for individual groups. The body height below the 3rd percentile was achieved around the 30th month for boys with Hurler syndrome, between the 4th and 5th year for patients with severe MPS II and between the 7th and 8th year for patients with attenuated MPS II.

CONCLUSIONS

The growth pattern differs between patients with MPS I and II. It reflects the clinical severity of MPS and may assist in the evaluation of clinical efficacy of available therapies.

Enzymatic replacement therapy for Hunter disease: Up to 9 years experience with 17 patients

Hunter disease is an X-linked lysosomal storage disorder characterized by progressive storage of glycosaminoglycans (GAGs) and multi-organ impairment. The central nervous system (CNS) is involved in at least 50% of cases. Since 2006, the enzymatic replacement therapy (ERT) is available but with no effect on the cognitive impairment, as the present formulation does not cross the blood-brain barrier. Here we report the outcome of 17 Hunter patients treated in a single center. Most of them (11) started ERT in 2006, 3 had started it earlier in 2004, enrolled in the phase III trial, and 3 after 2006, as soon as the diagnosis was made. The liver and spleen sizes and urinary GAGs significantly decreased and normalized throughout the treatment. Heart parameters improved, in particular the left ventricular mass index/m(2) decreased significantly. Amelioration of hearing was seen in many patients. Joint range of motion improved in all patients. However, no improvement on respiratory function, eye, skeletal and CNS disease was found. The developmental quotient of patients with a CNS involvement showed a fast decline. These patients were no more testable after 6 years of age and, albeit the benefits drawn from ERT, their quality of life worsened throughout the years. The whole group of patients showed a consistent residual disease burden mainly represented by persistent skeletal disease and frequent need of surgery. This study suggests that early diagnosis and treatment and other different therapies which are able to cross the blood-brain barrier, might in the future improve the MPS II outcome.

Cervical spine MRI findings in patients with Mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II; Hunter syndrome) is an X-linked, recessive, lysosomal storage disorder caused by deficiency of iduronate-2-sulfatase (EC 3.1.6.13). The purpose of this report is to describe cervical spine magnetic resonance (MRI) findings in MPS II patients and to correlate them with clinical phenotype. Seven cervical spine MRI examinations from Polish MPS II patients (mean age 11.4 years, median age 8 years, range 5-30) were evaluated. Six patients were classified as neurological (85.7%) and 1 as attenuated (14.3%). Five patients were treated with idursulfase (range 110-260 weeks, mean 195, median 200), while 2 patients never received the treatment. The following features were assessed: periodontoid thickening, spinal stenosis, dens hypoplasia, myelopathy, and vertebral and intervertebral disc abnormalities. Mean age at evaluation was 11 years (range 5-30, median 8). Cervical spine MRI was abnormal in all the patients and the most frequent abnormalities found were dens hypoplasia (100%), periodontoid thickening (100%), disc abnormalities (100%) and spinal stenosis (43%). There was no clear correlation between MRI findings and patients' phenotypes.