Metachromatic leukodystrophy (MLD) is a rare hereditary neurodegenerative disease caused by deficiency of the lysosomal enzyme arylsulfatase A (ARSA). This study described the clinical and molecular characteristics of 24 Chinese children with MLD and investigated functional characterization of five novel ARSA variants. A retrospective analysis was performed in 24 patients diagnosed with MLD at Guangzhou Women and Children\'s Medical Center in South China. Five novel mutations were further characterized by transient expression studies. We recruited 17 late-infantile, 3 early-juvenile, 4 late-juvenile MLD patients. In late-infantile patients, motor developmental delay and gait disturbance were the most frequent symptoms at onset. In juvenile patients, cognitive regression and gait disturbance were the most frequent chief complaints. Overall, 25 different ARSA mutations were identified with 5 novel mutations.The most frequent alleles were p.W320* and p.G449Rfs. The mutation p.W320*, p.Q155=, p.P91L, p.G156D, p.H208Mfs*46 and p.G449Rfs may link to late-infantile type. The novel missense mutations were predicted damaging in silico. The bioinformatic structural analysis of the novel missense mutations showed that these amino acid replacements would cause severe impairment of protein structure and function. In vitro functional analysis of the six mutants, showing a low ARSA enzyme activity, clearly demonstrated their pathogenic nature. The mutation p.D413N linked to R alleles. In western blotting analysis of the ARSA protein, the examined mutations retained reduced amounts of ARSA protein compared to the wild type. This study expands the spectrum of genotype of MLD. It helps to the future studies of genotype-phenotype correlations to estimate prognosis and develop new therapeutic approach.

BACKGROUND: Arylsulfatase A (ARSA), a lysosomal enzyme, has been shown to inhibit the aggregation and propagation of α-synuclein (α-syn) through its molecular chaperone function. The relationship between ARSA levels and Parkinson\'s disease (PD) in the Chinese Han population remains controversial, and few quantitative research studies have investigated the relationship between plasma ARSA levels and PD.
OBJECTIVE: The purpose of this study was to investigate the relationships between ARSA levels and cognitive function in PD patients and to evaluate the association of ARSA and α-syn levels with nonmotor symptoms.
METHODS: Enzyme-linked immunosorbent assay (ELISA) was used to measure the plasma ARSA and α-syn levels in 50 healthy controls, 120 PD patients (61 PD patients with no cognitive impairment (PD-NCI) and 59 PD patients with cognitive impairment (PD-CI)). Motor symptoms and nonmotor symptoms (cognitive function, Unified Parkinson\'s Disease Rating Scale (UPDRS) score, depression, anxiety, constipation, olfactory dysfunction, sleep disruption, and other symptoms) were assessed with the relevant scales. The Kruskal-Wallis H test was used for comparison between groups, and Pearson/Spearman analysis was used for correlation analysis.
RESULTS: The plasma ARSA concentrations were lower in the PD-CI group than in the PD-NCI group. The plasma α-syn levels in the PD-CI group were higher than those in the healthy control group, and the plasma ARSA levels were correlated with the Mini-Mental State Examination (MMSE scores) and Hoehn and Yahr (H-Y) stage.
CONCLUSIONS: We used a quantitative assessment method to show that low plasma ARSA levels and high α-syn levels are related to cognitive impairment in PD patients. Plasma ARSA levels gradually decrease with PD progression.

Metachromatic leukodystrophy disorder (MLD) is an autosomal recessive lysosomal storage disease. The disease is primarily caused by a deficiency in the enzyme arylsulfatase A (ASA), which is encoded by the ARSA gene. A total of 254 mutations have been reported in different populations. The present study aimed to detect causative gene mutations in an atypical case presenting with attention deficit hyperactivity disorder through whole-exome sequencing. Of note, the patient\'s mother is from a consanguineous family. Compound heterozygous variants (c.1297C>G) + (c.1345G>A) [(p.Leu433Val) + (p.Gly449Arg)] were identified in exon 8 in the ARSA gene of the pediatric patient. The two missense mutations identified have not been previously reported, to the best of our knowledge. Furthermore, an in silico analysis and multiple phylogenetic tree analyses of ARSA homologs were performed to predict the effects of the two novel mutations. Serial changes were observed in the patient with MLD at follow-up visits over 6 years. However, brain MRI images demonstrated no notable progression and the number of ASA enzymes was stable. Also, the results of neurodevelopmental assessment showed that the patient was diagnose with ADHD. These data may offer a potential explanation of the genotype-phenotype correlation in MLD and enhance the spectrum of mutations associated with the condition.

BACKGROUND: Metachromatic leukodystrophy (MLD) is a rare inherited lysosomal storage disorder caused mainly by variants in arylsulfatase A (ARSA) gene. MLD can be divided into three major clinical forms according to the age of onset: late infantile, juvenile, and adult. We report two siblings of late infantile MLD presenting with cerebellar ataxia as the only first clinical symptom.
METHODS: Because of the unspecific neurological manifestation, whole-exome sequencing (WES) was performed to find disease-causing mutations for molecular diagnosis. Then successive MRI and ARSA activity determination were performed to further confirm the diagnosis. Moreover, the prenatal diagnosis was carried out on the basis of molecular diagnosis.
RESULTS: The siblings exhibited compound heterozygous variants {[c.302G>T]+[c.1344dupC]} in the ARSA gene, and both of the variants have been reported as disease-causing mutations previously. The results of MRI and low ARSA activity confirmed the diagnosis of MLD. Prenatal diagnosis showed that the fetus was a heterozygous carrier.
CONCLUSIONS: It is recommended that WES be considered as a first line diagnostic procedure to discover potential disease-causing genetic variants in affected individuals with hereditary traits but without definite clinical diagnosis. However, the final diagnosis should be confirmed by comprehensive evaluations including biochemical, enzymatic or imaging investigations.