Clinical characteristics and surgical history of Taiwanese patients with mucopolysaccharidosis type II: data from the hunter outcome survey (HOS)

Causes of death in mucopolysaccharidoses

Mucopolysaccharidoses are inherited metabolic diseases caused by mutations in genes encoding enzymes required for degradation of glycosaminoglycans. A lack or severe impairment of activity of these enzymes cause accumulation of GAGs which is the primary biochemical defect. Depending on the kind of the deficient enzyme, there are 12 types and subtypes of MPS distinguished. Despite the common primary metabolic deficit (inefficient GAG degradation), the course and symptoms of various MPS types can be different, though majority of the diseases from the group are characterized by severe symptoms and significantly shortened live span. Here, we analysed the frequency of specific, direct causes of death of patients with different MPS types, the subject which was not investigated comprehensively to date. We examined a total of 1317 cases of death among MPS patients, including 393 cases of MPS I, 418 cases of MPS II, 232 cases of MPS III, 45 cases of MPS IV, 208 cases of MPS VI, and 22 cases of MPS VII. Our analyses indicated that the most frequent causes of death differ significantly between MPS types, with cardiovascular and respiratory failures being predominant in MPS I, MPS II, and MPS VI, neurological deficits in MPS III, respiratory issues in MPS IV, and hydrops fetalis in MPS VII. Results of such studies suggest what specific clinical problems should be considered with the highest priority in specific MPS types, apart from attempts to correct the primary causes of the diseases, to improve the quality of life of patients and to prolong their lives.

Clinical characteristics and genotypes of 201 patients with mucopolysaccharidosis type II in China: A retrospective, observational study

Mucopolysaccharidosis type II (MPS II) is an X-linked recessive lysosomal storage disease caused by a disease-associated variant in the IDS gene, which encodes iduronate 2-sulfatase (IDS). We aimed to characterize the clinical characteristics and genotypes of the largest cohort of Chinese patients with MPS II and so gain a deeper understanding of natural disease progression. Patients with confirmed MPS II and without treatment were included. The disease was classified as severe in patients with neurological impairment, and as attenuated in patients aged >6 years without neurological impairment. Of the 201 male patients, 78.1% had severe MPS II. Cognitive regression occurred before age 6 years in 94.3% of patients. Of 122 IDS variants identified, 37 were novel. Among the large gene alteration types identified, only the frequency of IDS-IDS2 recombination was significantly higher in severe versus attenuated MPS II (P = 0.032). Some identified point variants could inform the understanding of genotype-phenotype correlations. In conclusion, this study showed that classification of the disease as attenuated should only be made in patients aged >6 years. Our findings expand the understanding of the genotype-phenotype relationship, inform the diagnostic process, and provide an indication of the likely prognosis.

Phenotypic and genetic characteristics of 130 patients with mucopolysaccharidosis type II: A single-center retrospective study in China

Background: Mucopolysaccharidosis Type II (MPS II) is a rare, progressive and ultimately fatal X-linked lysosomal storage disorder caused by mutations in the iduronate-2-sulfatase (IDS) gene. This report conducted a retrospective analysis to investigate the clinical characteristics, genotypes and management strategies in a large cohort of Chinese patients with MPS II. Methods: In this study, we explored 130 Chinese patients with MPS II between September 2008 and April 2022. Clinical manifestations, auxiliary examination, IDS pathogenic gene variants and IDS enzyme activity, surgical history were analysed in the study. Results: A total of 130 patients were enrolled and the mean age at diagnosis was 5 years old. This study found the most common symptoms in our patients were claw-like hands, followed by coarse facial features, birthmarks (Mongolian spot), delayed development, inguinal or umbilical hernia. The most commonly cardiac manifestations were valve abnormalities, which were mitral/tricuspid valve regurgitation (71.9%) and aortic/pulmonary valve regurgitation (36.8%). We had found 43 different IDS pathogenic gene variants in 55 patients, included 16 novel variants. The variants were concentrated in exon 9 (20% = 11/55), exon 3 (20% = 11/55) and exon 8 (15% = 8/55). A total of 50 patients (38.5%) underwent surgical treatment, receiving a total of 63 surgeries. The average age of first surgery was 2.6 years, and the majority of surgery (85.7%, 54/63) was operated before 4 years old. The most common and earliest surgery was hernia repair. Three patients were died of respiratory failure. Conclusion: This study provided additional information on the clinical, cardiac ultrasound and surgical procedure in MPS II patients. Our study expanded the genotype spectrum of MPS II. Based on these data, characterization of MPS II patients group could be used to early diagnosis and treatment of the disease.

Newborn Screening Program for Mucopolysaccharidosis Type II and Long-Term Follow-Up of the Screen-Positive Subjects in Taiwan

Background: Mucopolysaccharidosis II (MPS II) is an X-linked disorder resulting from a deficiency in lysosomal enzyme iduronate-2-sulfatase (IDS), which causes the accumulation of glycosaminoglycans (GAGs) in the lysosomes of many tissues and organs, leading to progressive cellular dysfunction. An MPS II newborn screening program has been available in Taiwan since 2015. The aim of the current study was to collect and analyze the long-term follow-up data of the screen-positive subjects in this program. Methods: From August 2015 to April 2022, 548,624 newborns were screened for MPS II by dried blood spots using tandem mass spectrometry, of which 202 suspected infants were referred to our hospital for confirmation. The diagnosis of MPS II was confirmed by IDS enzyme activity assay in leukocytes, quantitative determination of urinary GAGs by mass spectrometry, and identification of the IDS gene variant. Results: Among the 202 referred infants, 10 (5%) with seven IDS gene variants were diagnosed with confirmed MPS II (Group 1), 151 (75%) with nine IDS gene variants were classified as having suspected MPS II or pseudodeficiency (Group 2), and 41 (20%) with five IDS gene variants were classified as not having MPS II (Group 3). Long-term follow-up every 6 months was arranged for the infants in Group 1 and Group 2. Intravenous enzyme replacement therapy (ERT) was started in four patients at 1, 0.5, 0.4, and 0.5 years of age, respectively. Three patients also received hematopoietic stem cell transplantation (HSCT) at 1.5, 0.9, and 0.6 years of age, respectively. After ERT and/or HSCT, IDS enzyme activity and the quantity of urinary GAGs significantly improved in all of these patients compared with the baseline data. Conclusions: Because of the progressive nature of MPS II, early diagnosis via a newborn screening program and timely initiation of ERT and/or HSCT before the occurrence of irreversible organ damage may lead to better clinical outcomes. The findings of the current study could serve as baseline data for the analysis of the long-term effects of ERT and HSCT in these patients.

Clinical Characteristics and Healthcare Resource Utilization for Patients with Mucopolysaccharidosis II (MPS II) in the United States: A Retrospective Chart Review

Background: Mucopolysaccharidosis II (MPS II; Hunter syndrome) is a rare, X-linked, life-limiting lysosomal storage disease characterized by a deficiency in the activity of the enzyme iduronate-2-sulfatase. Accumulation of glycosaminoglycans in tissues and organs throughout the body causes cellular damage, leading to multisystemic disease manifestations. Patients generally require multidisciplinary care across a wide range of specialties. Objectives: The aims of this study were to assess the healthcare needs of patients with MPS II and to explore the impact of treatment on disease burden and healthcare resource utilization. Methods: A retrospective review of medical charts from 19 US sites was performed. Data were analyzed from 140 male patients diagnosed with MPS II (defined as a documented deficiency in iduronate-2-sulfatase) between 1997 and 2017. The prevalence and age at onset of clinical manifestations and extent and frequency of healthcare resource use were evaluated. Results: Of the patients in this study, 77.1% had received enzyme replacement therapy with intravenous idursulfase and 62.1% had cognitive impairment. The clinical burden among patients was substantial: almost all patients had ear, nose, and throat abnormalities (95.7%); musculoskeletal abnormalities (95.0%); and joint stiffness or abnormalities (90.7%). Of the most prevalent disease manifestations, facial dysmorphism and hepatosplenomegaly were documented the earliest (median age at first documentation of 3.8 years in both cases). Hospitalizations, emergency department visits, and outpatient visits were reported for 51.2%, 58.5%, and 93.5% of patients, respectively, with a frequency of 0.1, 0.2, and 3.0 per patient per year, respectively. Surgery was also common, with 91.1% of patients having undergone at least 1 surgical procedure. The clinical burden and prevalence and frequency of resource use were generally similar in patients who had received enzyme replacement therapy and in those who had not. Conclusions: These results add to our understanding of the natural history of MPS II and indicate that the disease burden and healthcare needs of patients with this progressive disease are extensive. Increased understanding of disease burden and resource use may enable the development of models of healthcare resource utilization in patients with MPS II and contribute to improvements in disease management and patient care.

Otorhinolaryngological Management in Taiwanese Patients with Mucopolysaccharidoses

Background: Mucopolysaccharidoses (MPSs) are lysosomal storage disorders wherein glycosaminoglycans accumulate because the enzymes that degrade them are insufficient. The earliest symptoms, which are the main reasons for seeking consultation, are otorhinolaryngological and commonly occur in MPS I, II, IV, and VI. This retrospective study aimed to determine the occurrence of otorhinolaryngological manifestations in MPS patients in Taiwan and to analyze the prognosis of surgical intervention, including its effect on symptoms. Methods: We reviewed 42 patients (30 males and 12 females), with a median age of 20.5 years, who had MPS (16.7% type I, 35.7% type II, 19.0% type IIIB, 21.4% type IVA, and 7.2% type VI). The following otorhinolaryngological manifestations were collected: annual number of upper respiratory tract infections (URTIs) and otitis media with effusion (OME) episodes, adenoid size, tonsillar size, and apnea-hypopnea index (AHI). Results: Among 42 patients, we found recurrent otitis media in 42.9% of the patients, hearing loss in 83.3% (mixed: 52.4%, conductive: 21.4%, and sensorineural: 9.5%), frequent URTIs in 47.6%, and obstructive sleep apnea syndrome in 35.7%. Moreover, 76% of the patients underwent ear, nose, and throat (ENT) surgery, including adenoidectomy, tonsillectomy, tympanostomy with ventilation tube insertion, tracheotomy, and supraglottoplasty. Conclusions: MPS patients had a high incidence of ENT problems. ENT surgery reduced the severity of hearing loss, degree of symptoms related to upper airway obstruction, and severity of respiratory tract and otological infections of patients with MPS.

Aortic Root Dilatation in Taiwanese Patients with Mucopolysaccharidoses and the Long-Term Effects of Enzyme Replacement Therapy

Background: Cardiovascular abnormalities have been observed in patients with mucopolysaccharidosis (MPS) of any type, with the most documented abnormalities being valvular regurgitation and stenosis and cardiac hypertrophy. Only a few studies have focused on aortic root dilatation and the long-term effects of enzyme replacement therapy (ERT) in these patients. Methods: We reviewed echocardiograms of 125 Taiwanese MPS patients (age range, 0.1 to 19.1 years; 11 with MPS I, 49 with MPS II, 25 with MPS III, 29 with MPS IVA, and 11 with MPS VI). The aortic root diameter was measured at the sinus of Valsalva. Results: Aortic root dilatation (z score >2) was observed in 47% of the MPS patients, including 66% of MPS IV, 51% of MPS II, 45% of MPS VI, 28% of MPS III, and 27% of MPS I patients. The mean aortic root diameter z score was 2.14 (n = 125). The patients with MPS IV had the most severe aortic root dilatation with a mean aortic root diameter z score of 3.03, followed by MPS II (2.12), MPS VI (2.06), MPS III (1.68), and MPS I (1.03). The aortic root diameter z score was positively correlated with increasing age (n = 125, p < 0.01). For the patients with MPS II, III, and IV, aortic root diameter z score was also positively correlated with increasing age (p < 0.01). For 16 patients who had received ERT and had follow-up echocardiographic data (range 2.0–16.2 years), the mean aortic root diameter z score change was −0.46 compared to baseline (baseline 2.49 versus follow-up 2.03, p = 0.490). Conclusions: Aortic root dilatation was common in the patients with all types of MPS, with the most severe aortic root dilatation observed in those with MPS IV. The severity of aortic root dilatation worsened with increasing age, reinforcing the concept of the progressive nature of this disease. ERT for MPS appears to stabilize the progression of aortic root dilatation.

Newborn screening for mucopolysaccharidoses: Measurement of glycosaminoglycans by LC-MS/MS

Mucopolysaccharidoses (MPS) are a family of lysosomal storage disorders which can lead to degenerative and irreversible skeletal, cardiovascular, pulmonary, and neurological damage. Current treatments, including hematopoietic stem cell transplantation and enzyme replacement therapy, have been found most effective if administered before clinical symptoms are present, highlighting the urgent need for the development of newborn screening.

This study analyzed 18,222 dried blood spot samples from newborns for both enzyme activity and glycosaminoglycan (GAG) concentration levels. GAG levels were measured using liquid chromatography tandem mass spectrometry. Results were compared to our previously established cutoff values for three subtypes of GAGs: dermatan sulfate (DS) and heparan sulfate (HS0S and HSNS). Samples that were high for two of the three GAGs were identified and screened a second time. Samples were also measured for iduronate-2-sulfatase and alfa-L-iduronidase activity.

A total of 300 samples were above the established cutoff values for at least two of the three GAGs after the first screening. One sample was determined through clinical and genetic testing to be a true positive for MPS II. The false positive rate after the first GAG screening was 1.64%. A Cochran's formula test showed that the samples available for the second screening were representative samples (p = .0000601). False positive rate after second GAG screening, extrapolated from the representative sample was 0.4%. False positive rate after enzyme activity assay by fluorimetry for IDUA and IDS enzymes was 0.21% and 0.18%. A combination of GAG and enzyme assays provided no false positive and false negative samples.

Two-tier screening involving a combination of enzyme activity and multiple GAGs should be considered the gold standard for the diagnosis of MPS patients.

An At-Risk Population Screening Program for Mucopolysaccharidoses by Measuring Urinary Glycosaminoglycans in Taiwan

Background: The mucopolysaccharidoses (MPSs) are a group of rare lysosomal storage disorders characterized by the accumulation of glycosaminoglycans (GAGs) and which eventually cause progressive damage to various tissues and organs. We developed a feasible MPS screening algorithm and established a cross-specialty collaboration platform between medical geneticists and other medical specialists based on at-risk criteria to allow for an earlier confirmative diagnosis of MPS. Methods: Children (<19 years of age) with clinical signs and symptoms compatible with MPS were prospectively enrolled from pediatric clinics between July 2013 and June 2018. Urine samples were collected for a non-specific total GAG analysis using the dimethylmethylene blue (DMB) spectrophotometric method, and the quantitation of three urinary GAGs (dermatan sulfate (DS), heparan sulfate (HS), and keratan sulfate (KS)) was performed by liquid chromatography/tandem mass spectrometry (LC-MS/MS). The subjects with elevated urinary GAG levels were recalled for leukocyte enzyme activity assay and genetic testing for confirmation. Results: Among 153 subjects enrolled in this study, 13 had a confirmative diagnosis of MPS (age range, 0.6 to 10.9 years—three with MPS I, four with MPS II, five with MPS IIIB, and one with MPS IVA). The major signs and symptoms with regards to different systems recorded by pediatricians at the time of the decision to test for MPS were the musculoskeletal system (55%), followed by the neurological system (45%) and coarse facial features (39%). For these 13 patients, the median age at the diagnosis of MPS was 2.9 years. The false negative rate of urinary DMB ratio using the dye-based method for these 13 patients was 31%, including one MPS I, two MPS IIIB, and one MPS IVA. However, there were no false negative results with urinary DS, HS and KS using the MS/MS-based method. Conclusions: We established an at-risk population screening program for MPS by measuring urinary GAG fractionation biomarkers using the LC-MS/MS method. The program included medical geneticists and other medical specialists to increase awareness and enable an early diagnosis by detecting MPS at the initial onset of clinical symptoms.

Transabdominal preperitoneal repair for an adolescent patient with Hunter syndrome: a case report

Background

Hunter syndrome is an X-linked disorder caused by a deficit of the lysosomal enzyme iduronate-2-sulfatase and is associated with many disorders. Patients with Hunter syndrome often develop inguinal hernias in early childhood and undergo Potts’ method, laparoscopic percutaneous extraperitoneal closure (LPEC), or laparoscopic direct suture.

Case presentation

An 18-year-old male visited our hospital for evaluation of a palpable mass in the right groin hernia. Computed tomography revealed a right indirect inguinal hernia. He had a history of repeated admission to our hospital and pediatric treatments for pneumonia, heart failure, and convulsions after birth. Because he has stopped growing and a wide hernia orifice was present with no apparent hernia on the left side, we performed TAPP repair. During surgery, we noted softness of the abdominal wall, similar to children’s abdominal wall, and laparoscopy revealed well-developed veins around the spermatic cord and testicular artery. The softness of the abdominal wall made insertion of the trocars difficult and well-developed veins needed our special care to avoid hemorrhage. After surgery, the patient developed a convulsion due to Hunter syndrome and subsequent aspiration pneumonia; however, he recovered with medical treatments administered in cooperation with specialists and was discharged on postoperative day 9.

Conclusion

This is the first reported patient with Hunter syndrome whose inguinal hernia was treated by TAPP repair. TAPP repair might be a useful procedure even for adolescent patients with Hunter syndrome, although adequate care is needed for symptoms due to Hunter syndrome.

Quantification of 11 enzyme activities of lysosomal storage disorders using liquid chromatography-tandem mass spectrometry

Lysosomal storage disorders (LSDs) are characterized by the accumulation of lipids, glycolipids, oligosaccharides, mucopolysaccharides, and other biological substances because of the pathogenic deficiency of lysosomal enzymes. Such diseases are rare; thus, a multiplex assay for these disorders is effective for the identification of affected individuals during the presymptomatic period. Previous studies have demonstrated that such assays can be performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with multiple reaction monitoring (MRM) detection. An assay procedure to quantify the activity of 11 enzymes associated with LSDs was provided. First, a validation study was performed using dried blood spot (DBS) samples with 100% and 5% enzyme activity for quality control (QC). Under the assay condition, the analytical range, defined as the ratio of the peak area of the enzyme reaction products from the DBS for QC with 100% enzyme activity to that from the filter paper blank sample, was between 14 for GALN and 4561 for GLA. Based on these results, the distribution of the enzyme activity for the 11 LSD enzymes was further examined. Consistent with the previous data, the enzyme activity exhibited a bell-shaped distribution with a single peak. The averaged enzyme activity for the healthy neonates was as follows: GLA, 3.80 ± 1.6; GAA, 10.6 ± 4.8; IDUA, 6.4 ± 2.3; ABG, 8.6 ± 3.1; ASM, 3.3 ± 1.1; GALC, 2.8 ± 1.3; ID2S, 16.7 ± 6.1; GALN, 1.2 ± 0.5; ARSB, 17.0 ± 8.7; NAGLU, 4.6 ± 1.5; and GUSB, 46.6 ± 19.0 μmol/h/L (mean ± SD, n = 200). In contrast, the enzyme activity in disease-affected individuals was lower than the minimum enzyme activity in healthy neonates. The results demonstrate that the population of disease-affected individuals was distinguished from that of healthy individuals by the use of LC-MS/MS.