Gaucher disease (GD, OMIM #230800 OMIM#230800) is a rare, autosomal recessive inherited metabolic disorder caused by mutation in GBA1 encoding the lysosomal enzyme, glucocerebrosidase. The deficiency of glucocerebrosidase leads to an accumulation of its substrate, glucosylceramide in macrophages of various tissues. Common clinical manifestations include cytopenia, splenomegaly, hepatomegaly, and bone lesions. The phenotype of GD is classified into three clinical categories: Type 1 (non-neuronopathic) is characterized by involvements on the viscera, whereas types 2 and 3 (neuronopathic) are associated with not only visceral symptoms but also neurological impairment, either severe in type 2 or variable in type 3. A diagnosis of GD can be confirmed by demonstrating the deficiency of acid glucocerebrosidase activity in leukocytes. Mutations in the GBA1 should be identified as they may be of prognostic value in some cases. Biomarkers including Chitotriosidase, CCL18, and glucosylsphingosine (lyso-GL1) are useful in diagnosis and treatment monitoring. Currently available disease-specific treatment in Korea consists of intravenous enzyme replacement therapy and substrate reduction therapy. For enhancing long-term prognosis, the onset of Parkinson's disease and Lewy body dementia, or the occurrence of a blood disease or cancer (hepatocellular carcinoma) should be monitored in older patients. The development of new strategies that can modify the neurological phenotype are expected, especially in Asia including Korea, where the prevalence of neuronopathic GD is relatively higher than that in western countries.

Glutaric aciduria type 1 (GA1; OMIM #231670) is a rare autosomal recessive-inherited neurometabolic disorder caused by the deficiency of glutaryl-CoA dehydrogenase (GCDH), which is encoded by the GCDH gene. It results in the accumulation of glutaric acid (GA), 3-hydroxyglutaric acid (3-OH-GA), glutaconic acid, and glutarylcarnitine (C5DC). These metabolites are considered to damage the striatum through an excitotoxic mechanism. The treatments of GA1 known to date are metabolic maintenance treatment based on a low-lysine diet and emergency treatment during acute illness. However, treatment after the onset of neurological symptoms has limited effectiveness and is associated with poor outcomes, and the effect of treatment and disease course after treatment are not good. After the implementation of newborn screening, the incidence of acute encephalopathic crisis fell to 10%-20% with early diagnosis, preventative dietary management, and aggressive medical intervention during acute episodes. Recently, several cohort studies have been published on the natural course and treatment of GA1 patients. This mini review will cover the clinical symptoms, natural history, and treatment of GA1 through a literature review.

Mucopolysaccharidosis type II (MPS II, Hunter syndrome) is an X-linked lysosomal storage disorder caused by deficiency of the enzyme iduronate-2-sulfatase, leading to the accumulation of glycosaminoglycans (GAGs), which affects multiple organs and systems. Current treatments for MPS II include enzyme replacement therapy (ERT) and hematopoietic cell transplantation (HCT) to reduce the accumulation of GAGs. HCT has the potential advantage that donor-derived enzyme-competent cells can provide a continuous secreting source of the enzyme. However, HCT as a treatment for MPS II remains controversial because its effectiveness is unclear, particularly in terms of neurological symptoms. To date, several clinical experiences with HCT in MPS II have been reported. In this paper, we review post-HCT outcomes in the previously published literature and discuss the effects of HCT on each of the clinical signs and symptoms of MPS II.

Hunter syndrome or mucopolysaccharidosis type II (MPS-II) (OMIM 309900) is a rare lysosomal storage disorder caused by deficiency in the activity of the enzyme iduronate-2-sulfatase. This enzyme is responsible for the catabolism of the following two different glycosaminoglycans (GAGs): dermatan sulfate and heparan sulfate. The lysosomal accumulation of these GAG molecules results in cell, tissue, and organ dysfunction. Patients can be broadly classified as having one of the following two forms of MPS II: a severe form and an attenuated form. In the severe form of the disease, signs and symptoms (including neurological impairment) develop in early childhood, whereas in the attenuated form, signs and symptoms develop in adolescence or early adulthood, and patients do not experience significant cognitive impairment. The involvement of the skeletal-muscle system is because of essential accumulated GAGs in joints and connective tissue. MPS II has many clinical features and includes two recognized clinical entities (mild and severe) that represent two ends of a wide spectrum of clinical severities. However, enzyme replacement therapy is likely to have only a limited impact on bone and joint disease based on the results of MPS II studies. The aim of this study was to review the involvement of joints in MPS II.

Mucopolysaccharidosis type III (MPS III) or Sanfilippo disease is an orphan-inherited lysosomal storage disease. It is one of the most common MPS subtypes. The classical presentation is an infantile-onset neurodegenerative disease characterized by intellectual regression, behavioral and sleep disturbances, loss of ambulation, and early death. Unlike other MPS, no disease-modifying therapy has been approved. Here, we review the curative therapy developed for MPS III, from historically ineffective hematopoietic stem cell transplantation and substrate reduction therapy to the promising enzyme replacement therapy or adeno-associated/lentiviral vector-mediated gene therapy. Preclinical studies are presented with recent translational first-in-man trials. We also present experimental research with preclinical mRNA and gene-editing strategies. Lessons from animal studies and clinical trials have highlighted the importance of early therapy before extensive neuronal loss. Disease-modifying therapy for MPS III will likely mandate the development of new early diagnosis strategies.

Prader-Willi Syndrome (PWS) is a neurodevelopmental genomic imprinting disorder involving a lack of gene expression from the paternal chromosome 15q11-q13 region. This is typically due to paternal 15q11-q13 deletions (in approximately 60% of cases), maternal uniparental disomy 15, or when both 15s are from the mother (about 35% of cases). An imprinting center controls the expression of imprinted genes in the chromosome 15q11-q13 region. PWS is a neurodevelopmental disorder characterized by mental retardation and distinct physical, behavioral, and psychiatric features. Characteristic behavioral disturbances in PWS include excessive interest in food, skin picking, difficulty with a change in routine, temper tantrums, obsessive and compulsive behaviors, and mood fluctuations. Individuals with PWS typically have intellectual disabilities (borderline to mild/moderate mental retardation) and exhibit a higher overall level of behavior disturbances compared to individuals with similar intellectual disabilities. This condition severely limits social adaptations and quality of life. Different factors have been linked to the intensity and form of these behavioral disturbances, but there is no consensus regarding the cause. Consequently, there is still controversy surrounding management strategies and there is a need for new data. PWS is a multisystem disorder. Family members, caregivers, physicians, dieticians, and speech-language pathologists all play an important role in the management and treatment of symptoms in an individual with PWS. Here we analyze behavioral problems in children and adults with PWS by age and review appropriate management and treatment strategies for these symptoms.

Prader-Willi syndrome is a complicated genetic disorder caused by a mutation on chromosome 15q11-13. The disease results in morbid obesity due to hyperphagia, growth disturbance, multiple endocrine problems from hypopituitarism, developmental delay, and cognitive or behavioral problems. Recombinant human growth hormone has been used to improve body composition and muscle mass, which plays a main role in treating patients with Prader-Willi syndrome. We describe previous studies showing the efficacy and safety of growth hormone treatment in children with Prader-Willi syndrome and provide treatment guidelines. Growth hormone therapy could be beneficial for children with Prader-Willi syndrome and improve their quality of life.

Prader-Willi syndrome (PWS) is a rare genetic neurodevelopmental disorder of hyperphagia leading to severe obesity, intellectual deficits, compulsivity, and other behavioral problems. PWS is caused by the inactivation of contiguous genes on chromosome 15q11-q13, which complicates the development of targeted, effective therapeutics. Various preclinical studies have been conducted by developing mouse models that exhibit phenotypes similar to PWS. Oxytocin deficiency in PWS is associated with hyperphagia with impaired satiety and, food-seeking and behavior disorders. Here, we summarize the oxytocin study of ingestion behavior tested in the PWS mouse model and published data from clinical trials that have evaluated treatment effectiveness on ingestion behavior and social dysfunction in patients with PWS.