Systemic gene dysregulation in classical Galactosaemia: Is there a central mechanism?

Classical Galactosaemia is a rare disorder of carbohydrate metabolism caused by a deficiency of galactose-1-phosphate uridyltransferase (GALT). The disease is life-threatening in the neonate, and the only treatment option is life-long dietary restriction of galactose. However, long-term complications persist in treated patients including cognitive impairments, speech and language abnormalities and premature ovarian insufficiency in females. Microarray analysis of T-lymphocytes from treated adult patients identified systemic dysregulation of numerous gene pathways, including the glycosylation, inflammatory and inositol pathways. Analysis of gene expression in patient-derived dermal fibroblasts of patients exposed to toxic levels of galactose, with immunostaining, has further identified the susceptibility of the glycosylation gene alpha-1,2-mannosyltransferase (ALG9) and the inflammatory gene annexin A1 (ANXA1) to increased galactose concentrations. These data suggest that Galactosaemia is a multi-system disorder affecting numerous signalling pathways.

Classical Galactosaemia in Ireland: incidence, complications and outcomes of treatment.

Newborn screening for the inborn error of metabolism, classical galactosaemia prevents life-threatening complications in the neonatal period. It does not however influence the development of long-term complications and the complex pathophysiology of this rare disease remains poorly understood. The objective of this study was to report the development of a healthcare database (using Distiller Version 2.1) to review the epidemiology of classical galactosaemia in Ireland since initiation of newborn screening in 1972 and the long-term clinical outcomes of all patients attending the National Centre for Inherited Metabolic Disorders (NCIMD). Since 1982, the average live birth incidence rate of classical galactosaemia in the total Irish population was approximately 1:16,476 births. This reflects a high incidence in the Irish 'Traveller' population, with an estimated birth incidence of 1:33,917 in the non-Traveller Irish population. Despite early initiation of treatment (dietary galactose restriction), the long-term outcomes of classical galactosaemia in the Irish patient population are poor; 30.6 % of patients ≥ 6 yrs have IQs <70, 49.6 % of patients ≥ 2.5 yrs have speech or language impairments and 91.2 % of females ≥ 13 yrs suffer from hypergonadotrophic hypogonadism (HH) possibly leading to decreased fertility. These findings are consistent with the international experience. This emphasizes the requirement for continued clinical research in this complex disorder.

IgG N-glycans as potential biomarkers for determining galactose tolerance in Classical Galactosaemia.

N-glycan processing and assembly defects have been demonstrated in untreated and partially treated patients with Classical Galactosaemia. These defects may contribute to the ongoing pathophysiology of this disease. The aim of this study was to develop an informative method of studying differential galactose tolerance levels and diet control in individuals with Galactosaemia, compared to the standard biochemical markers. Ten Galactosaemia adults with normal intellectual outcomes were analyzed in the study. Five subjects followed galactose liberalization, increments of 300 mg to 4000 mg/day over 16 weeks, and were compared to five adult Galactosaemia controls on a galactose restricted diet. All study subjects underwent clinical and biochemical monitoring of red blood cell galactose-1-phosphate (RBC Gal-1-P) and urinary galactitol levels. Serum N-glycans were isolated and analyzed by normal phase high-performance liquid chromatography (NP-HPLC) with galactosylation of IgG used as a specific biomarker of galactose tolerance. IgG N-glycan profiles showed consistent individual alterations in response to diet liberalization. The individual profiles were improved for all, but one study subject, at a galactose intake of 1000 mg/day, with decreases in agalactosylated (G0) and increases in digalactosylated (G2) N-glycans. We conclude that IgG N-glycan profiling is an improved method of monitoring variable galactosylation and determining individual galactose tolerance in Galactosaemia compared to the standard methods.

Reversible infantile respiratory chain deficiency is a unique, genetically heterogenous mitochondrial disease.

OBJECTIVES: Homoplasmic maternally inherited, m.14674T>C or m. 14674T>G mt-tRNA(Glu) mutations have recently been identified in reversible infantile cytochrome c oxidase deficiency (or 'benign COX deficiency'). This study sought other genetic defects that may give rise to similar presentations. PATIENTS: Eight patients from seven families with clinicopathological features of infantile reversible cytochrome c oxidase deficiency were investigated. METHODS: The study reviewed the diagnostic features and performed molecular genetic analyses of mitochondrial DNA and nuclear encoded candidate genes. RESULTS: Patients presented with subacute onset of profound hypotonia, feeding difficulties and lactic acidosis within the first months of life. Although recovery was remarkable, a mild myopathy persisted into adulthood. Histopathological findings in muscle included increased lipid and/or glycogen content, ragged-red and COX negative fibres. Biochemical studies suggested more generalised abnormalities than pure COX deficiency. Clinical improvement was reflected by normalisation of lactic acidosis and histopathological abnormalities. The m.14674T>C mt-tRNA(Glu) mutation was identified in four families, but none had the m. 14674T>G mutation. Furthermore, in two families pathogenic mutations were also found in the nuclear TRMU gene which has not previously been associated with this phenotype. In one family, the genetic aetiology still remains unknown. CONCLUSIONS: Benign COX deficiency is better described as 'reversible infantile respiratory chain deficiency'. It is genetically heterogeneous, and patients not carrying the m.14674T>C or T>G mt-tRNA(Glu) mutations may have mutations in the TRMU gene. Diagnosing this disorder at the molecular level is a significant advance for paediatric neurologists and intensive care paediatricians, enabling them to select children with an excellent prognosis for continuing respiratory support from those with severe mitochondrial presentation in infancy.

Designing rare disease care pathways in the Republic of Ireland: a co-operative model.

BACKGROUND: Rare diseases (RDs) are often complex, serious, chronic and multi-systemic conditions, associated with physical, sensory and intellectual disability. Patients require follow-up management from multiple medical specialists and health and social care professionals involving a high level of integrated care, service coordination and specified care pathways. METHODS AND OBJECTIVES: This pilot study aimed to explore the best approach for developing national RD care pathways in the Irish healthcare system in the context of a lack of agreed methodology. Irish clinical specialists and patient/lived experience experts were asked to map existing practice against evidence-based clinical practice guidelines (CPGs) and best practice recommendations from the European Reference Networks (ERNs) to develop optimal care pathways. The study focused on the more prevalent, multisystemic rare conditions that require multidisciplinary care, services, supports and therapeutic interventions. RESULTS: 29 rare conditions were selected across 18 ERNs, for care pathway development. Multidisciplinary input from multiple specialisms was relevant for all pathways. A high level of engagement was experienced from clinical leads and patient organisations. CPGs were identified for 26 of the conditions. Nurse specialist, Psychology, Medical Social Work and Database Manager roles were deemed essential for all care pathways. Access to the therapeutic Health Service Professionals: Physiotherapy, Occupational Therapy, and Speech and Language Therapy were seen as key requirements for holistic care. Genetic counselling was highlighted as a core discipline in 27 pathways demonstrating the importance of access to Clinical Genetics services for many people with RDs. CONCLUSIONS: This study proposes a methodology for Irish RD care pathway development, in collaboration with patient/service user advocates. Common RD patient needs and health care professional interventions across all pathways were identified. Key RD stakeholders have endorsed this national care pathway initiative. Future research focused on the implementation of such care pathways is a priority.

Negative screening tests in classical galactosaemia caused by S135L homozygosity.

Classical galactosaemia is relatively common in Ireland due to a high carrier rate of the Q188R GALT mutation. It is screened for using a bacterial inhibition assay (BIA) for free galactose. A Beutler assay on day one of life is performed only in high risk cases (infants of the Traveller community and relatives of known cases). A 16-month-old Irish-born boy of Nigerian origin was referred for investigation of developmental delay, and failure to thrive. He had oral aversion to solids and his diet consisted of cow's milk and milk-based cereal mixes. He was found to have microcephaly, weight <2nd percentile, hepatomegaly and bilateral cataracts. Coagulation screen was normal and transaminases were slightly elevated. His original newborn screen was reviewed and confirmed to have been negative; urinary reducing substances on three separate occasions were negative. Beutler assay demonstrated "absent" red cell galactose-1-phosphate uridyltransferase (GALT) activity. GALT enzyme activity was <0.5 gsubs/h per gHb confirming classical galactosaemia. Gal-1-P was elevated at 1.88 micromol/gHb. Mutation analysis of the GALT gene revealed S135L homozygosity. S135L/S135L galactosaemia is associated with absent red cell GALT activity but with approximately 10% activity in other tissues such as the liver and intestines, probably explaining the negative screening tests and the somewhat milder phenotype associated with this genotype. The patient was commenced on galactose-restricted diet; on follow-up at 2 years of age, growth had normalized but there was global developmental delay. In conclusion, galactosaemia must be considered in children who present with poor growth, hepatomegaly, developmental delay and cataracts and GALT enzyme analysis should be a first line test in such cases. Non-enzymatic screening methods such as urinary reducing substances and BIA for free galactose are not reliable in S135L homozygous galactosaemia.

Further pitfalls in the diagnosis of mtDNA mutations: homoplasmic mt-tRNA mutations.

BACKGROUND: Mitochondrial DNA (mtDNA) mutations are important causes of human genetic disease, with mutations in tRNA genes particularly prevalent. In many patients, mutations are heteroplasmic, affecting a population of mtDNA molecules. Establishing the pathogenicity of homoplasmic mitochondrial tRNA (mt-tRNA) mutations, in which the mutation is present in every mtDNA molecule, is extremely difficult. These mutations must conform to specific pathogenic criteria, documenting unequivocally a functional defect of the mutant mt-tRNA. AIMS: To investigate the pathogenic nature of two homoplasmic mt-tRNA(Thr) deletions, m.15940delT (previously reported as pathogenic) and m.15937delA, by assessing the steady state levels of the mutant mt-tRNA in tissue and cell-line samples from six unrelated families, in which affected individuals were thoroughly investigated for mitochondrial DNA disease on the basis of clinical presentations. Rates of de novo mitochondrial protein synthesis were also examined in control and m.15937delA mutant fibroblasts. RESULTS: Our data strongly suggest that both single nucleotide deletions are neutral polymorphisms; no obvious defects were apparent in either steady state mt-tRNA(Thr) levels or rates of mitochondrial protein synthesis. CONCLUSIONS: These findings have important implications for the investigation of other families with suspected mtDNA disease, in particular the requirement to fulfil strict and established pathogenic criteria in order to avoid misattribution of pathogenicity to mt-tRNA variants.

The natural history of classic galactosemia: lessons from the GalNet registry.

BACKGROUND: Classic galactosemia is a rare inborn error of carbohydrate metabolism, caused by a severe deficiency of the enzyme galactose-1-phosphate uridylyltransferase (GALT). A galactose-restricted diet has proven to be very effective to treat the neonatal life-threatening manifestations and has been the cornerstone of treatment for this severe disease. However, burdensome complications occur despite a lifelong diet. For rare diseases, a patient disease specific registry is fundamental to monitor the lifespan pathology and to evaluate the safety and efficacy of potential therapies. In 2014, the international Galactosemias Network (GalNet) developed a web-based patient registry for this disease, the GalNet Registry. The aim was to delineate the natural history of classic galactosemia based on a large dataset of patients. METHODS: Observational data derived from 15 countries and 32 centers including 509 patients were acquired between December 2014 and July 2018. RESULTS: Most affected patients experienced neonatal manifestations (79.8%) and despite following a diet developed brain impairments (85.0%), primary ovarian insufficiency (79.7%) and a diminished bone mineral density (26.5%). Newborn screening, age at onset of dietary treatment, strictness of the galactose-restricted diet, p.Gln188Arg mutation and GALT enzyme activity influenced the clinical picture. Detection by newborn screening and commencement of diet in the first week of life were associated with a more favorable outcome. A homozygous p.Gln188Arg mutation, GALT enzyme activity of ≤ 1% and strict galactose restriction were associated with a less favorable outcome. CONCLUSION: This study describes the natural history of classic galactosemia based on the hitherto largest data set.

Sensory-motor polyneuropathy occurring in variant maple syrup urine disease.

Maple syrup urine disease (MSUD; OMIM 248600) results from an inherited deficiency of the branched-chain ketoacid dehydrogenase (BCKD) complex. Approximately 20% of patients with BCKD deficiency are non-classic variants of MSUD with differing clinical severity. Outcomes for this cohort are generally favourable; episodes of metabolic decompensation do not appear to correlate with adverse events if acute management is promptly provided. A case of predominantly axonal sensory-motor neuropathy following metabolic decompensation which persisted for a number of months is presented in an adolescent girl with variant (intermediate type) MSUD. EMG and nerve conduction studies suggested a pre-existent asymptomatic chronic neuropathy, exacerbated by the acute decompensation. Peak leucine concentration at decompensation was 1083 µmol/L. The patient had laboratory signs of secondary mitochondrial respiratory chain dysfunction at presentation. She had been on a moderate dose of thiamine prior to decompensation; thiamine and pyridoxine blood concentrations were normal. This, to our knowledge, is the first report of a neuropathy presenting in a patient with a decompensation of variant MSUD. We propose that this presentation resembles the intermittent neuropathy observed in pyruvate dehydrogenase deficiency and may reflect secondary inhibition of pyruvate dehydrogenase activity by MSUD metabolites.

Extended Experience of Lower Dose Sapropterin in Irish Adults with Mild Phenylketonuria.

Adherence to dietary and treatment recommendations is a long-standing concern for adults and adolescents with PKU and treating clinicians. In about 20-30% of PKU patients, Phe levels may be controlled by tetrahydrobiopterin (BH4) therapy. The European PKU 2017 Guidelines recommends treatment with BH4 for cases of proven long-term BH4 responsiveness, with a recommended dosage of Sapropterin 10-20 mg/kg/day.We report four young Irish patients with mild PKU, known to be BH4 responsive, who were treated with lower doses of Sapropterin for over 7 years.Case 1: Female, currently age 20. Genotype p. 165T/p/F39L, c.[194T>C]; [117C>G]. Newborn Phe: 851 µmol/L. Pre-Sapropterin Phe tolerance: 600 mg Phe/day to maintain Phe levels <400 µmol/L. Commenced on Sapropterin 400 mg (6.5 mg/kg/day) with increase in Phe tolerance to 800 mg/day.Case 2: Female, currently age 23. Genotype p. 165T/pF39L; c.[194T>C]; [117C>G]. Newborn Phe: 714 µmol/L. Pre-Sapropterin Phe tolerance: 700 mg Phe/day. Commenced on Sapropterin 400 mg (8 mg/kg/day) with increase in Phe tolerance to 800 mg/day.Case 3: Male, currently age 22. Genotype p. 165T/p.S349P; c.[194T>C][1045T>C]. Newborn Phe: 1,036 µmol/L. Pre-Sapropterin Phe tolerance: 600 mg Phe/day. Commenced on Sapropterin 400 mg (5.4 mg/kg/day). Increased to 1,600 mg Phe/day.Case 4: Female, currently age 29. Genotype p.R408W/p/p.Y414C; c.[1222C>T], [1241A>G]. Newborn Phe: 1,600 µmol/L. Pre-Sapropterin tolerance: 450 mg/day. Commenced on Sapropterin 400 mg (5.0 mg/kg/day). Increased to 900 mg Phe/day.Almost 7 years of surveillance for these four patients has shown that this dose of Sapropterin (range 5-8 mg/kg day) was well tolerated and effective with a significant response to treatment and a marked improvement in quality of life at these lower Sapropterin doses.

Mitochondrial cytopathies, phenotypic heterogeneity and a high incidence.

Mitochondrial respiratory chain disorders account for significant and varied presentations in paediatric practice. The true prevalence of these disorders in the paediatric population is still not well documented with predicted geographic variation. We report a retrospective analysis over a seven year period of cases presenting to a tertiary care centre and associated clinical features. The overall prevalence of mitochondrial disorders in our population is higher than expected (1/9,000 births), explained in part by multiple presentations in a consanguineous subgroup of the population (Irish travellers).

Unexplained developmental delay/learning disability: guidelines for best practice protocol for first line assessment and genetic/metabolic/radiological investigations.

BACKGROUND: Investigation of patients, particularly children, with unexplained global developmental delay (GDD)/learning disability (LD) has been challenging due to a lack of clear guidance from specialised centres. Limited knowledge of rare diseases and a poor understanding of the purpose or limitations of appropriate investigations have been some of the principal reasons for this difficulty. AIMS: A guideline development group was formed to recommend on appropriate, first line metabolic, genetic and radiological investigations for children and adults with unexplained GDD/ID. METHODS AND RECOMMENDATIONS: A comprehensive literature search was conducted, evaluated and reviewed by the guideline committee and a best practice protocol for first line assessment and genetic, metabolic and radiological investigations was decided upon after considering diagnostic yield, practicality, treatability and costs. CONCLUSION: It is hoped that these recommendations will become national guidelines for the first line metabolic, genetic and radiological investigation of patients presenting with unexplained GDD/ID.

A novel deletion in the flavin-containing monooxygenase gene (FMO3) in a Greek patient with trimethylaminuria.

Mutations of the flavin-containing monooxygenase type 3 gene (FMO3) that encode the major functional form present in adult human liver, have been shown to cause trimethylaminuria. We now report a novel homozygous deletion of exons 1 and 2 in an Australian of Greek ancestry with TMAuria, the first report of a deletion causative of trimethylaminuria. The deletion occurs 328 bp upstream from exon 1. The 3'-end of the deletion occurs in intron 2, 10013 base pairs downstream from the end of exon 2. The deletion is 12226 bp long. For the proband homozygous for the human FMO3 gene deletion, it is predicted that in addition to loss of monooxygenase function for human FMO3 substrates, such as TMA and other amines, the proband will exhibit decreased tolerance of biogenic amines, both medicinal and those found in foods.

'Celtic' phenylketonuria chromosomes found? Evidence in two regions of Quebec Province.

We analyzed mutations, RFLP haplotypes (H), and a VNTR polymorphism at the phenylalanine hydroxylase locus (PAH) in 12 French-Canadian patients with phenylketonuria (PKU) from the eastern region of Quebec province and 13 non-French-Canadian PKU patients from the Montreal region. There were 10 different mutation/H/VNTR haplotype combinations on the 50 PKU chromosomes: one set of 5 and another of 8 accounted for 88 and 77% of these chromosomes in the French-Canadian and non-French-Canadian patients, respectively. The differences in PKU haplotypes between the two groups of probands reflect the different histories of the two populations. Three PKU haplotype combinations were shared by the two groups: IVS12nt1:H-3:VNTR-8, I65T:H-9:VNTR-8, and R408W:H-1:VNTR-8. The IVS12nt1 mutation (18% of the total sample) is prevalent in northern Europeans. The I65T-H-9 and R408W:H-1 haplotypes have seldom been reported in Europeans but when encountered tend to be found in northwestern regions. The R408W mutation is usually on H-2 in Europeans. In Quebec the R408W:H-1 and I65T:H-9 haplotypes accounted for 20% of PKU chromosomes, clustered in two geographic regions, and in every family where they occurred an Irish or Scottish ('Celtic') ancestor could be inferred. We propose that I65T:H-9:VNTR-8 and R408W:H-1:VNTR-8 chromosomes are markers for a diaspora of 'Celtic' descendants. Our findings predict the distributions of these unusual PKU haplotypes in contemporary Europeans.

Mutation at the phenylalanine hydroxylase gene (PAH) and its use to document population genetic variation: the Quebec experience.

We describe variation at the PAH locus in the population of Quebec. We successfully analyzed 135 of 141 chromosomes from phenylketonuria (PKU) probands (95.7% of the sample), and eight additional chromosomes from a small number of probands with non-PKU hyperphenylalaninemia (HPA). The full set of chromosomes harboured 45 different PAH mutations: i) seven polymorphisms (IVS2nt19, IVS3nt-22, IVS6nt-55, Q232Q, V245V, L385L, Y414Y); ii) four mutations causing non-PKU HPA (T92I, E390G, R408Q, D415N); iii) 34 mutations causing PKU. Only six mutations (M1V, R261Q, F299C, S349P, R408W and IVS12nt1) occurred in the whole province at relative frequencies > 5%: most are rare and probably identical by descent. By studying associations of mutations with polymorphic haplotype alleles, we found examples of mutations on different haplotypes that were identical by state, but not by descent because they were recurrent mutations (E280K and R408W); and examples of mutations identical both by state and by descent because of intragenic recombination (S67P, G218V, V245A and IVS12nt1). Ten mutations were first described in Quebec and five are still unique there; three of these 'Quebec' mutations are reported here for the first time (c.125A-->T (K42I); [c.470G-->A; c.471A--C] (R157N); c.707nt-55 (IVS6nt-55). The PAH mutations stratify by geographic region and population, their distributions validating hypotheses about European range expansion to North America during three separate phases of immigration and demographic expansion in the Quebec region over the past four centuries. The PAH homozygosity value (j) is 0.06 for the total Quebec sample (0.5-0.08 by regions), and the corresponding homoallelic fraction of mutant PAH genotypes is 24%. These findings are a documentation of genetic diversity in the Quebec population.

Fenofibrate raises plasma homocysteine levels in the fasted and fed states.

The effect of fenofibrate (FEN), compared with placebo (PL), on total plasma homocysteine (tHcy) levels in the fasted and fed states has been examined. Twenty men with established coronary artery disease (CAD) or with at least two cardiovascular risk factors, who had elevated plasma triglyceride levels (> 2.3 mmol/l) and reduced HDL-C levels (< 0.91 mmol/l), and in whom a fibric acid derivative was clinically indicated were studied. The study was a randomized, PL controlled, double-blind study designed to test the effect of micronized FEN on postprandial lipemia. Plasma tHcy levels were investigated as a post-hoc analysis. After a 4-week dietary stabilization period, patients were randomized to PL or FEN (200 mg/day) for 8 weeks, followed by an 8-h postprandial study, consisting of 1 g fat/kg body weight (35% cream). The methionine content of cream was approximately 0.53 mg/ml. A 5-week washout period was then followed by a second 8-week treatment period (FEN or PL), at the end of which a second postprandial study was undertaken. Blood was sampled in the fasted state (0 h) and postprandially at 2, 4, 6 and 8 h. Plasma was stored at -80 degrees C for homocysteine, vitamins B(6), B(12) and folate measurements. FEN caused a marked decrease in all triglyceride-rich lipoprotein parameters, no change in LDL-C, and an increase in HDL-C levels. Fen treatment was associated with an increase in fasting tHcy (PL: 10.3+/-3.3 micromol/l to FEN: 14.1+/-3.8 micromol/l, 40.4+/-20.5%, P < 0.001) and fed tHcy levels 6 h post-fat load (PL: 11.6+/-3.3 micromol/l vs. FEN: 17.1+/-5.4 micromol/l, P < 0.001). Homocysteine levels were increased by the fat load; PL: 14% (P < 0.001) and FEN: 21%, P < 0.001 at the 2, 4, 6 and 8 h time points. Change in tHcy level on FEN was not associated with changes in plasma levels of folate, vitamins B(6) or B(12) or creatinine. Amino acid analysis revealed that methionine and cysteine were significantly increased on FEN (P < 0.005). The incidence of hyperhomocysteinemia (defined as tHcy level >14 micromol/l) was PL: 2/20 (10%) and FEN: 9/20 (45%) (chi(2) = 4.51, P = 0.034). There was no correlation between changes in plasma triglyceride levels and tHcy levels. Since tHcy is considered an emerging cardiovascular risk factor, the ability of FEN to increase plasma tHcy levels could potentially mitigate the potential of this drug to protect against cardiovascular disease.

Neonatal seizures and limb malformations associated with liver-specific complex IV respiratory chain deficiency.

An eight-week-old infant, the fourth child of consanguineous parents presented with intractable neonatal seizures. The mother had two previous miscarriages. The infant initially presented on day one with multifocal myoclonus, complex partial and generalised tonic-clonic seizures. On examination, there were dysmorphic hands and feet, with absent nails and terminal phalanges of the fingers and toes, hepatomegaly, marked axial and peripheral hypotonia and severe global developmental delay. Ophthalmological assessment showed 'salt and pepper' pigmentary retinopathy. The urinary organic acid profile revealed a marked increase in tricarboxylic acid metabolites. Urinary phosphate reabsorption was reduced at 84%. Type I fibre atrophy was seen on muscle histology, and a cytochrome c oxidase deficiency was found only on enzymology of liver tissue. Limb malformations associated with respiratory chain defects have rarely been reported. To our knowledge, this child has the most severe limb anomaly associated with a tissue-specific complex IV respiratory chain defect.

Variable onset of metachromatic leukodystrophy in a Vietnamese family.

We report two siblings with metachromatic leukodystrophy, one who presented at 7 years of age (juvenile onset) and his sister who presented at 22 years of age (adult onset). They are compound heterozygotes for two novel mutations in the arylsufatase A gene (ARSA). The responsible mutations in this Vietnamese family consist of a missense mutation with 5% enzyme activity (R143G) and a nonsense mutation (W318ter), from which no enzyme activity would be expected. These mutations in the ARSA gene have not been previously reported and may be useful when diagnosing metachromatic leukodystrophy in other affected Vietnamese individuals. The variability in presentation suggests that the genotype alone is not sufficient to determine the onset and course of the disease and modifying genetic and perhaps nongenetic factors likely contribute.