Long-term follow-up of an attenuated presentation of NAXE-related disease, a potentially actionable neurometabolic disease: a case report

Background

Early-onset progressive encephalopathy with brain edema and/or leukoencephalopathy (PEBEL-1) is an autosomal recessive disorder whereby a fluctuating clinical course is exacerbated by febrile illnesses. Pathogenic NAD(P)HX epimerase (NAXE) gene mutations underpin this disorder. This mutation damages the metabolite repair system involved in regenerating crucial redox carriers. Longer survival has rarely been reported in this potentially actionable entity.

Objectives

This case study aims to report a milder phenotype of a patient with NAXE gene mutation and his longitudinal follow-up of more than 20 years.

Case report

A 24-year-old man first became symptomatic in infancy with frequent initial neurological decompensations in the setting of infections with subsequent clinical improvement followed by stability with residual cerebellar dysfunction. Clinical features noted over the years include chronic ataxia, nystagmus, ptosis, mild spasticity of lower limbs, and neuropsychiatric symptoms. Cerebellar and spinal cord atrophy were noted in cranial and spinal MR imaging. Biallelic homozygous variants in the NAXE gene (c.733 A>C) were identified on whole exome sequencing. Symptom management included the initiation of a mitochondrial cocktail with carnitine, coenzyme Q, and thiamine. Subsequently, niacin (Vitamin B3), which is involved in the cellular biosynthesis of NAD+, was added, given its potentially beneficial therapeutic impact.

Conclusion

A missense homozygous variant in the NAXE gene is described in this patient with a milder clinical phenotype of the disease. Supplementation with niacin in addition to a mitochondrial cocktail presents a potential supportive therapeutic option to reduce disease progression.

A milder form of molybdenum cofactor deficiency type A presenting as Leigh's syndrome-like phenotype highlighting the secondary mitochondrial dysfunction: a case report

Background

Molybdenum cofactor deficiency (MoCD) (OMIM# 252150) is an autosomal-recessive disorder caused by mutations in four genes involved in the molybdenum cofactor (MOCO) biosynthesis pathway.

Objectives

We report a milder phenotype in a patient with MOCS1 gene mutation who presented with a Leigh-like presentation.

Case report

We present the case of a 10-year-old boy who was symptomatic at the age of 5 months with sudden onset of dyskinesia, nystagmus, and extrapyramidal signs following a febrile illness. Initial biochemical, radiological, and histopathological findings a Leigh syndrome-like phenotype; however, whole-exome sequencing detected compound heterozygous mutations in MOCS1 gene, c.1133 G>C and c.217C>T, confirming an underlying MoCD. This was biochemically supported by low uric acid level of 80 (110-282 mmol/L) and low cystine level of 0 (3-49), and a urine S-sulfocysteine at 116 (0-15) mmol/mol creatinine. The patient was administered methionine- and cystine-free formulas. The patient has remained stable, with residual intellectual, speech, and motor sequelae.

Conclusion

This presentation expands the phenotypic variability of late-onset MoCD A and highlights the role of secondary mitochondrial dysfunction in its pathogenesis.

Persistent hematopoietic polyclonality after lentivirus-mediated gene therapy for Fabry disease

The safety and efficacy of lentivirus-mediated gene therapy was recently demonstrated in five male patients with Fabry disease-a rare X-linked lysosomal storage disorder caused by GLA gene mutations that result in multiple end-organ complications. To evaluate the risks of clonal dominance and leukemogenesis, which have been reported in multiple gene therapy trials, we conducted a comprehensive DNA insertion site analysis of peripheral blood samples from the five patients in our gene therapy trial. We found that patients had a polyclonal integration site spectrum and did not find evidence of a dominant clone in any patient. Although we identified vector integrations near proto-oncogenes, these had low percentages of contributions to the overall pool of integrations and did not persist over time. Overall, we show that our trial of lentivirus-mediated gene therapy for Fabry disease did not lead to hematopoietic clonal dominance and likely did not elevate the risk of leukemogenic transformation.

Autologous, lentivirus-modified, T-rapa cell "micropharmacies" for lysosomal storage disorders

T cells are the current choice for many cell therapy applications. They are relatively easy to access, expand in culture, and genetically modify. Rapamycin‐conditioning ex vivo reprograms T cells, increasing their memory properties and capacity for survival, while reducing inflammatory potential and the amount of preparative conditioning required for engraftment. Rapamycin‐conditioned T cells have been tested in patients and deemed to be safe to administer in numerous settings, with reduced occurrence of infusion‐related adverse events. We demonstrate that ex vivo lentivirus‐modified, rapamycin‐conditioned CD4⁺ T cells can also act as next‐generation cellular delivery vehicles—that is, “micropharmacies”—to disseminate corrective enzymes for multiple lysosomal storage disorders. We evaluated the therapeutic potential of this treatment platform for Fabry, Gaucher, Farber, and Pompe diseases in vitro and in vivo. For example, such micropharmacies expressing α‐galactosidase A for treatment of Fabry disease were transplanted in mice where they provided functional enzyme in key affected tissues such as kidney and heart, facilitating clearance of pathogenic substrate after a single administration.

Expanding the phenotypic and molecular spectrum of NFS1-related disorders that cause functional deficiencies in mitochondrial and cytosolic iron-sulfur cluster containing enzymes

Iron-sulfur cluster proteins are involved in critical functions for gene expression regulation and mitochondrial bioenergetics including the oxidative phosphorylation system. The c.215G>A p.(Arg72Gln) variant in NFS1 has been previously reported to cause infantile mitochondrial complex II and III deficiency. We describe three additional unrelated patients with the same missense variant. Two infants with the same homozygous variant presented with hypotonia, weakness and lactic acidosis, and one patient with compound heterozygous p.(Arg72Gln) and p.(Arg412His) variants presented as a young adult with gastrointestinal symptoms and fatigue. Skeletal muscle biopsy from patients 1 and 3 showed abnormal mitochondrial morphology, and functional analyses demonstrated decreased activity in respiratory chain complex II and variably in complexes I and III. We found decreased mitochondrial and cytosolic aconitase activities but only mildly affected lipoylation of pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase enzymes. Our studies expand the phenotypic spectrum and provide further evidence for the pathogenicity and functional sequelae of NFS1-related disorders with disturbances in both mitochondrial and cytosolic iron-sulfur cluster containing enzymes.

An Unexpected Finding of Hepatosplenomegaly in a Pediatric Patient

Gaucher disease (GD) is a rare autosomal recessive metabolic disorder. It is characterized by a deficiency of lysosomal glucocerebrosidase, which results in the accumulation of glycosphingolipid substrates, primarily glucosylceramide, in the phagocyte system. In GD Type 1, the liver, spleen, and bone marrow are typically affected. We report the case of a 7-year-old female with GD Type 1 who presented with hepatosplenomegaly detected incidentally following a motor vehicle accident. She was found to have concomitant thrombocytopenia and Erlenmeyer flask deformities of her lower limbs. Diagnosis was made on the basis of very low leukocyte β-glucocerebrosidase activity and elevated plasma chitotriosidase. DNA mutation studies revealed both c.1226A>G and c.116_1505 deletion (exons 3-11). The patient is currently managed with biweekly intravenous imiglucerase (Cerezyme) replacement therapy. She demonstrated resolution of thrombocytopenia and hepatosplenomegaly at 2-year follow-up. Physicians must consider this rare diagnosis in children presenting with hepatosplenomegaly to prompt timely management.

Symptomatic mosaicism for a novel FBN1 splice site variant in a parent causing inherited neonatal Marfan syndrome

Neonatal Marfan syndrome is a severe, early onset presentation of pathogenic variants in FBN1. Because of the significant cardiac involvement and early mortality, nearly all reported cases have been de novo, and the disorder has not been documented to be inherited from a symptomatic parent. Here, we present a female infant with neonatal Marfan syndrome who was born to a father with Marfan syndrome. Prior to the birth of his daughter, the father had been found to have an FBN1 missense variant of uncertain clinical significance. Initial familial variant testing of the infant did not reveal the same missense variant, but Sanger sequencing of FBN1 subsequently identified a pathogenic splice site variant. The father was then found to have 10%-20% mosaicism for the same splice site variant.

Lentivirus-mediated gene therapy for Fabry disease

Enzyme and chaperone therapies are used to treat Fabry disease. Such treatments are expensive and require intrusive biweekly infusions; they are also not particularly efficacious. In this pilot, single-arm study (NCT02800070), five adult males with Type 1 (classical) phenotype Fabry disease were infused with autologous lentivirus-transduced, CD34⁺-selected, hematopoietic stem/progenitor cells engineered to express alpha-galactosidase A (α-gal A). Safety and toxicity are the primary endpoints. The non-myeloablative preparative regimen consisted of intravenous melphalan. No serious adverse events (AEs) are attributable to the investigational product. All patients produced α-gal A to near normal levels within one week. Vector is detected in peripheral blood and bone marrow cells, plasma and leukocytes demonstrate α-gal A activity within or above the reference range, and reductions in plasma and urine globotriaosylceramide (Gb₃) and globotriaosylsphingosine (lyso-Gb₃) are seen. While the study and evaluations are still ongoing, the first patient is nearly three years post-infusion. Three patients have elected to discontinue enzyme therapy.

Treatments for Fabry disease, an inherited lysosomal disorder caused by the deficiency of the enzyme alpha-galactosidase A, are not fully efficacious. Here the authors report a single-arm phase I trial of gene therapy with autologous, lentivirus-transduced, hematopoietic cells that express alpha-galactosidase A to demonstrate that this approach is safe in five patients with Fabry disease.

Bone marrow-derived mitochondrial DNA has limited capacity for inter-tissue transfer in vivo

Studies have shown that mitochondrial DNA (mtDNA) can be exchanged between tissues; however, the mechanism(s) behind this phenomenon remain unclear. Exosomes and other extracellular vesicles (EVs) including microvesicles (MV) have been shown to contain mtDNA. EVs can be derived from a number of tissues; however, the source and relative proportion of EVs containing mtDNA remains unknown. We sampled whole blood and the EV fractions (exosome-enriched, MV-enriched, and apoptotic body-enriched) as well as several tissues (epithelial-cheek and urine sediment), connective (fibroblasts), and skeletal muscle in two subjects who received allogenic bone marrow transplants. Next generation sequencing of the mtDNA confirmed that all EV fractions contained mtDNA and most was derived from the donor, confirming that most of the EV fractions in the serum are bone marrow/blood cell-derived. Even after exposure to the donor mtDNA in EV fractions (and potentially free in the plasma) for years, there was little to no transfer of the donor mtDNA to the host mtDNA fraction in epithelial, connective, or skeletal muscle tissues. These data call into question the potential therapeutic use of bone marrow transplant or EV-based delivery systems for mtDNA-based disorders and establish bone marrow as the primary source of most of the mtDNA enriched EVs in serum.

Use of complementary and alternative medicine in patients with inborn errors of metabolism: A single-center study

Background and Objectives

There is a paucity of information on the use of complementary and alternative medicine (CAM) in patients with inborn errors of metabolism (IEM). This study's objective was to evaluate the self-reported use and perceived effectiveness of CAM in adults and children with IEM.

Methods

Patients aged 0-70 years and caregivers seen at the London Health Sciences Centre Metabolic Clinic (London, Ontario, Canada) between July 2017 and August 2017 were recruited to complete a questionnaire regarding CAM use to help their IEM diagnosis and perceived effectiveness of these therapies. Survey responses were analyzed using descriptive statistics; age, sex, and education level associations among CAM users were tested using the Pearson χ ² test.

Results

Of 50 potential participants, 44 (88%) completed the questionnaire, including 21 adults (6 by caregivers) and 23 children (22 by caregivers). The most common IEM category was Aminoacidopathies and Small Molecule Disorders (50%). Twenty-seven (61%) participants reported CAM use to help their IEM diagnosis. The most common CAM therapies used were chiropractic manipulation, omega-3 fatty acids, probiotics, and aromatherapy/essential oils. Most CAM users and caregivers (74%) perceived their CAM therapies as effective overall. Among CAM users, 40% had not discussed CAM use with a health care professional (HCP). CAM use was similar when comparing age, sex and education level.

Conclusions

CAM is commonly used among patients with IEM. The safety and efficacy of CAM therapies for IEM should be further investigated. HCPs and patients should openly discuss CAM use in order to evaluate safety.

Ambroxol as a novel disease-modifying treatment for Parkinson's disease dementia: protocol for a single-centre, randomized, double-blind, placebo-controlled trial

BACKGROUND

Currently there are no disease-modifying treatments for Parkinson's disease dementia (PDD), a condition linked to aggregation of the protein α-synuclein in subcortical and cortical brain areas. One of the leading genetic risk factors for Parkinson's disease is being a carrier in the gene for β-Glucocerebrosidase (GCase; gene name GBA1). Studies in cell culture and animal models have shown that raising the levels of GCase can decrease levels of α-synuclein. Ambroxol is a pharmacological chaperone for GCase and is able to raise the levels of GCase and could therefore be a disease-modifying treatment for PDD. The aims of this trial are to determine if Ambroxol is safe and well-tolerated by individuals with PDD and if Ambroxol affects cognitive, biochemical, and neuroimaging measures.

METHODS

This is a phase II, single-centre, double-blind, randomized placebo-controlled trial involving 75 individuals with mild to moderate PDD. Participants will be randomized into Ambroxol high-dose (1050 mg/day), low-dose (525 mg/day), or placebo treatment arms. Assessments will be undertaken at baseline, 6-months, and 12-months follow up times. Primary outcome measures will be the Alzheimer's disease Assessment Scale-cognitive subscale (ADAS-Cog) and the ADCS Clinician's Global Impression of Change (CGIC). Secondary measures will include the Parkinson's disease Cognitive Rating Scale, Clinical Dementia Rating, Trail Making Test, Stroop Test, Unified Parkinson's disease Rating Scale, Purdue Pegboard, Timed Up and Go, and gait kinematics. Markers of neurodegeneration will include MRI and CSF measures. Pharmacokinetics and pharmacodynamics of Ambroxol will be examined through plasma levels during dose titration phase and evaluation of GCase activity in lymphocytes.

DISCUSSION

If found effective and safe, Ambroxol will be one of the first disease-modifying treatments for PDD.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02914366, 26 Sep 2016/retrospectively registered.

Identification of a novel synaptic protein, TMTC3, involved in periventricular nodular heterotopia with intellectual disability and epilepsy

Defects in neuronal migration cause brain malformations, which are associated with intellectual disability (ID) and epilepsy. Using exome sequencing, we identified compound heterozygous variants (p.Arg71His and p. Leu729ThrfsTer6) in TMTC3, encoding transmembrane and tetratricopeptide repeat containing 3, in four siblings with nocturnal seizures and ID. Three of the four siblings have periventricular nodular heterotopia (PVNH), a common brain malformation caused by failure of neurons to migrate from the ventricular zone to the cortex. Expression analysis using patient-derived cells confirmed reduced TMTC3 transcript levels and loss of the TMTC3 protein compared to parental and control cells. As TMTC3 function is currently unexplored in the brain, we gathered support for a neurobiological role for TMTC3 by generating flies with post-mitotic neuron-specific knockdown of the highly conserved Drosophila melanogaster TMTC3 ortholog, CG4050/tmtc3. Neuron-specific knockdown of tmtc3 in flies resulted in increased susceptibility to induced seizures. Importantly, this phenotype was rescued by neuron-specific expression of human TMTC3, suggesting a role for TMTC3 in seizure biology. In addition, we observed co-localization of TMTC3 in the rat brain with vesicular GABA transporter (VGAT), a presynaptic marker for inhibitory synapses. TMTC3 is localized at VGAT positive pre-synaptic terminals and boutons in the rat hypothalamus and piriform cortex, suggesting a role for TMTC3 in the regulation of GABAergic inhibitory synapses. TMTC3 did not co-localize with Vglut2, a presynaptic marker for excitatory neurons. Our data identified TMTC3 as a synaptic protein that is involved in PVNH with ID and epilepsy, in addition to its previously described association with cobblestone lissencephaly.

The Usher Syndrome Type IIIB Histidyl-tRNA Synthetase Mutation Confers Temperature Sensitivity

Histidyl-tRNA synthetase (HARS) is a highly conserved translation factor that plays an essential role in protein synthesis. HARS has been implicated in the human syndromes Charcot-Marie-Tooth (CMT) Type 2W and Type IIIB Usher (USH3B). The USH3B mutation, which encodes a Y454S substitution in HARS, is inherited in an autosomal recessive fashion and associated with childhood deafness, blindness, and episodic hallucinations during acute illness. The biochemical basis of the pathophysiologies linked to USH3B is currently unknown. Here, we present a detailed functional comparison of wild-type (WT) and Y454S HARS enzymes. Kinetic parameters for enzymes and canonical substrates were determined using both steady state and rapid kinetics. Enzyme stability was examined using differential scanning fluorimetry. Finally, enzyme functionality in a primary cell culture was assessed. Our results demonstrate that the Y454S substitution leaves HARS amino acid activation, aminoacylation, and tRNA^His binding functions largely intact compared with those of WT HARS, and the mutant enzyme dimerizes like the wild type does. Interestingly, during our investigation, it was revealed that the kinetics of amino acid activation differs from that of the previously characterized bacterial HisRS. Despite the similar kinetics, differential scanning fluorimetry revealed that Y454S is less thermally stable than WT HARS, and cells from Y454S patients grown at elevated temperatures demonstrate diminished levels of protein synthesis compared to those of WT cells. The thermal sensitivity associated with the Y454S mutation represents a biochemical basis for understanding USH3B.

Lentivector Iterations and Pre-Clinical Scale-Up/Toxicity Testing: Targeting Mobilized CD34+ Cells for Correction of Fabry Disease

Fabry disease is a rare lysosomal storage disorder (LSD). We designed multiple recombinant lentivirus vectors (LVs) and tested their ability to engineer expression of human α-galactosidase A (α-gal A) in transduced Fabry patient CD34⁺ hematopoietic cells. We further investigated the safety and efficacy of a clinically directed vector, LV/AGA, in both ex vivo cell culture studies and animal models. Fabry mice transplanted with LV/AGA-transduced hematopoietic cells demonstrated α-gal A activity increases and lipid reductions in multiple tissues at 6 months after transplantation. Next we found that LV/AGA-transduced Fabry patient CD34⁺ hematopoietic cells produced even higher levels of α-gal A activity than normal CD34⁺ hematopoietic cells. We successfully transduced Fabry patient CD34⁺ hematopoietic cells with “near-clinical grade” LV/AGA in small-scale cultures and then validated a clinically directed scale-up transduction process in a GMP-compliant cell processing facility. LV-transduced Fabry patient CD34⁺ hematopoietic cells were subsequently infused into NOD/SCID/Fabry (NSF) mice; α-gal A activity corrections and lipid reductions were observed in several tissues 12 weeks after the xenotransplantation. Additional toxicology studies employing NSF mice xenotransplanted with the therapeutic cell product demonstrated minimal untoward effects. These data supported our successful clinical trial application (CTA) to Health Canada and opening of a “first-in-the-world” gene therapy trial for Fabry disease.

A novel ICK mutation causes ciliary disruption and lethal endocrine-cerebro-osteodysplasia syndrome

Background

Endocrine-cerebro-osteodysplasia (ECO) syndrome [MIM:612651] caused by a recessive mutation (p.R272Q) in Intestinal cell kinase (ICK) shows significant clinical overlap with ciliary disorders. Similarities are strongest between ECO syndrome, the Majewski and Mohr-Majewski short-rib thoracic dysplasia (SRTD) with polydactyly syndromes, and hydrolethalus syndrome. In this study, we present a novel homozygous ICK mutation in a fetus with ECO syndrome and compare the effect of this mutation with the previously reported ICK variant on ciliogenesis and cilium morphology.

Results

Through homozygosity mapping and whole-exome sequencing, we identified a second variant (c.358G > T; p.G120C) in ICK in a Turkish fetus presenting with ECO syndrome. In vitro studies of wild-type and mutant mRFP-ICK (p.G120C and p.R272Q) revealed that, in contrast to the wild-type protein that localizes along the ciliary axoneme and/or is present in the ciliary base, mutant proteins rather enrich in the ciliary tip. In addition, immunocytochemistry revealed a decreased number of cilia in ICK p.R272Q-affected cells.

Conclusions

Through identification of a novel ICK mutation, we confirm that disruption of ICK causes ECO syndrome, which clinically overlaps with the spectrum of ciliopathies. Expression of ICK-mutated proteins result in an abnormal ciliary localization compared to wild-type protein. Primary fibroblasts derived from an individual with ECO syndrome display ciliogenesis defects. In aggregate, our findings are consistent with recent reports that show that ICK regulates ciliary biology in vitro and in mice, confirming that ECO syndrome is a severe ciliopathy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13630-016-0029-1) contains supplementary material, which is available to authorized users.

The expanding phenotype of MELAS caused by the m.3291T > C mutation in the MT-TL1 gene

m.3291T > C mutation in the MT-TL1 gene has been infrequently encountered in association with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS), however remains poorly characterized from a clinical perspective. In the following report we describe in detail the phenotypic features, long term follow up (> 7 years) and management in a Caucasian family with MELAS due to the m.3291T > C mutation and review the literature on m.3291T > C mutation. The clinical phenotype in the proposita included overlapping features of MELAS, MERRF (Myoclonic epilepsy and ragged-red fiber syndrome), MNGIE (Mitochondrial neurogastrointestinal encephalopathy), KSS (Kearns-Sayre Syndrome) and CPEO (Chronic progressive external ophthalmoplegia).

Biotinidase deficiency: Spectrum of molecular, enzymatic and clinical information from newborn screening Ontario, Canada (2007-2014)

Untreated profound biotinidase deficiency results in a wide range of clinical features, including optic atrophy, cutaneous abnormalities, hearing loss and developmental delay. Ontario, Canada incorporated this treatable deficiency in newborn screening over the past 8years. This study elucidates the molecular, biochemical, and clinical findings from the pilot project. Information from initial screens, serum biotinidase activity level assays, molecular testing, and family history for 246 positive newborns screens were analyzed. A mutation spectrum was created for the province of Ontario, including common mutations such as D444H, D444H/A171T, Q456H, C33fs, and R157H. Individuals with partial deficiency were separated into 3 groups: D444H homozygotes (Group 1); compound heterozygotes for D444H with another profound allele (Group 2); compound heterozygotes with two non-D444H alleles (Group 3). Biochemical phenotype-genotype associations in partial deficiency showed a significant difference in serum biotinidase activity in between any given two groups. Three children with partial deficiency discontinued biotin for varied lengths of time. Two of whom became symptomatic with abnormal gait, alopecia, skin rashes and developmental delay. A need for more congruency in diagnostic, treatment and educational practices was highlighted across the province. Heterogeneity and variation in clinical presentations and management was observed in patients with the partial deficiency.

Simulated diabetic ketoacidosis therapy in vitro elicits brain cell swelling via sodium-hydrogen exchange and anion transport

A common complication of type 1 diabetes mellitus is diabetic ketoacidosis (DKA), a state of severe insulin deficiency. A potentially harmful consequence of DKA therapy in children is cerebral edema (DKA-CE); however, the mechanisms of therapy-induced DKA-CE are unknown. Our aims were to identify the DKA treatment factors and membrane mechanisms that might contribute specifically to brain cell swelling. To this end, DKA was induced in juvenile mice with the administration of the pancreatic toxins streptozocin and alloxan. Brain slices were prepared and exposed to DKA-like conditions in vitro. Cell volume changes were imaged in response to simulated DKA therapy. Our experiments showed that cell swelling was elicited with isolated DKA treatment components, including alkalinization, insulin/alkalinization, and rapid reductions in osmolality. Methyl-isobutyl-amiloride, a nonselective inhibitor of sodium-hydrogen exchangers (NHEs), reduced cell swelling in brain slices elicited with simulated DKA therapy (in vitro) and decreased brain water content in juvenile DKA mice administered insulin and rehydration therapy (in vivo). Specific pharmacological inhibition of the NHE1 isoform with cariporide also inhibited cell swelling, but only in the presence of the anion transport (AT) inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid. DKA did not alter brain NHE1 isoform expression, suggesting that the cell swelling attributed to the NHE1 was activity dependent. In conclusion, our data raise the possibility that brain cell swelling can be elicited by DKA treatment factors and that it is mediated by NHEs and/or coactivation of NHE1 and AT.

Old gene, new phenotype: mutations in heparan sulfate synthesis enzyme, EXT2 leads to seizure and developmental disorder, no exostoses

BACKGROUND

Heparan sulfate proteoglycans are vital components of the extracellular matrix and are essential for cellular homeostasis. Many genes are involved in modulating heparan sulfate synthesis, and when these genes are mutated, they can give rise to early-onset developmental disorders affecting multiple body systems. Herein, we describe a consanguineous family of four sibs with a novel disorder, which we designate as seizures-scoliosis-macrocephaly syndrome, characterised by seizures, intellectual disability, hypotonia, scoliosis, macrocephaly, hypertelorism and renal dysfunction.

METHODS

Our application of autozygosity mapping and whole-exome sequencing allowed us to identify mutations in the patients. To confirm the autosomal-recessive mode of inheritance, all available family members were genotyped. We also studied the effect of these mutations on protein expression and function in patient cells and using an in vitro system.

RESULTS

We identified two homozygous mutations p.Met87Arg and p.Arg95 Cys in exostosin 2, EXT2, a ubiquitously expressed gene that encodes a glycosyltransferase required for heparan sulfate synthesis. In patient cells, we observed diminished EXT2 expression and function. We also performed an in vitro assay to determine which mutation has a larger effect on protein expression and observed reduced EXT2 expression in constructs expressing either one of the mutations but a greater reduction when both residues were mutated.

CONCLUSIONS

In short, we have unravelled the genetic basis of a new recessive disorder, seizures-scoliosis-macrocephaly syndrome. Our results have implicated a well-characterised gene in a new developmental disorder and have further illustrated the spectrum of phenotypes that can arise due to errors in glycosylation.

Lentivector integration sites in ependymal cells from a model of metachromatic leukodystrophy: non-B DNA as a new factor influencing integration

The blood–brain barrier controls the passage of molecules from the blood into the central nervous system (CNS) and is a major challenge for treatment of neurological diseases. Metachromatic leukodystrophy is a neurodegenerative lysosomal storage disease caused by loss of arylsulfatase A (ARSA) activity. Gene therapy via intraventricular injection of a lentiviral vector is a potential approach to rapidly and permanently deliver therapeutic levels of ARSA to the CNS. We present the distribution of integration sites of a lentiviral vector encoding human ARSA (LV-ARSA) in murine brain choroid plexus and ependymal cells, administered via a single intracranial injection into the CNS. LV-ARSA did not exhibit a strong preference for integration in or near actively transcribed genes, but exhibited a strong preference for integration in or near satellite DNA. We identified several genomic hotspots for LV-ARSA integration and identified a consensus target site sequence characterized by two G-quadruplex-forming motifs flanking the integration site. In addition, our analysis identified several other non-B DNA motifs as new factors that potentially influence lentivirus integration, including human immunodeficiency virus type-1 in human cells. Together, our data demonstrate a clinically favorable integration site profile in the murine brain and identify non-B DNA as a potential new host factor that influences lentiviral integration in murine and human cells.

Update on transcobalamin deficiency: clinical presentation, treatment and outcome

Transcobalamin (TC) transports cobalamin from blood into cells. TC deficiency is a rare autosomal recessive disorder usually presenting in early infancy with failure to thrive, weakness, diarrhoea, pallor, anemia, and pancytopenia or agammaglobulinemia. It can sometimes resemble neonatal leukemia or severe combined immunodeficiency disease. Diagnosis of TC deficiency is suspected based on megaloblastic anemia, elevation of total plasma homocysteine, and blood or urine methylmalonic acid. It is confirmed by studying the synthesis of TC in cultured fibroblasts, or by molecular analysis of the TCN2 gene. TC deficiency is treatable with supplemental cobalamin, but the optimal type, route and frequency of cobalamin administration and long term patient outcomes are unknown. Here we present a series of 30 patients with TC deficiency, including an update on multiple previously published patients, in order to evaluate the different treatment strategies and provide information about long term outcome. Based on the data presented, current practice appears to favour treatment of individuals with TC deficiency by intramuscular injections of hydroxy- or cyanocobalamin. In most cases presented, at least weekly injections (1 mg IM) were necessary to ensure optimal treatment. Most centres adjusted the treatment regimen based on monitoring CBC, total plasma homocysteine, plasma and urine methylmalonic acid, as well as, clinical status. Finally, continuing IM treatment into adulthood appears to be beneficial.

Exome sequencing identifies NFS1 deficiency in a novel Fe-S cluster disease, infantile mitochondrial complex II/III deficiency

Iron-sulfur (Fe-S) clusters are a class of highly conserved and ubiquitous prosthetic groups with unique chemical properties that allow the proteins that contain them, Fe-S proteins, to assist in various key biochemical pathways. Mutations in Fe-S proteins often disrupt Fe-S cluster assembly leading to a spectrum of severe disorders such as Friedreich's ataxia or iron-sulfur cluster assembly enzyme (ISCU) myopathy. Herein, we describe infantile mitochondrial complex II/III deficiency, a novel autosomal recessive mitochondrial disease characterized by lactic acidemia, hypotonia, respiratory chain complex II and III deficiency, multisystem organ failure and abnormal mitochondria. Through autozygosity mapping, exome sequencing, in silico analyses, population studies and functional tests, we identified c.215G>A, p.Arg72Gln in NFS1 as the likely causative mutation. We describe the first disease in man likely caused by deficiency in NFS1, a cysteine desulfurase that is implicated in respiratory chain function and iron maintenance by initiating Fe-S cluster biosynthesis. Our results further demonstrate the importance of sufficient NFS1 expression in human physiology.

A mutation in the serine protease TMPRSS4 in a novel pediatric neurodegenerative disorder

Background

To elucidate the genetic basis of a novel neurodegenerative disorder in an Old Order Amish pedigree by combining homozygosity mapping with exome sequencing.

Methods and results

We identified four individuals with an autosomal recessive condition affecting the central nervous system (CNS). Neuroimaging studies identified progressive global CNS tissue loss presenting early in life, associated with microcephaly, seizures, and psychomotor retardation; based on this, we named the condition Autosomal Recessive Cerebral Atrophy (ARCA). Using two unbiased genetic approaches, homozygosity mapping and exome sequencing, we narrowed the candidate region to chromosome 11q and identified the c.995C > T (p.Thr332Met) mutation in the TMPRSS4 gene. Sanger sequencing of additional relatives confirmed that the c.995C > T genotype segregates with the ARCA phenotype. Residue Thr332 is conserved across species and among various ethnic groups. The mutation is predicted to be deleterious, most likely due to a protein structure alteration as demonstrated with protein modelling.

Conclusions

This novel disease is the first to demonstrate a neurological role for a transmembrane serine proteases family member. This study demonstrates a proof-of-concept whereby combining exome sequencing with homozygosity mapping can find the genetic cause of a rare disease and acquire better understanding of a poorly described protein in human development.

Infantile Sialic Acid Storage Disease: Two Unrelated Inuit Cases Homozygous for a Common Novel SLC17A5 Mutation

Infantile sialic acid storage disease (ISSD) is a lysosomal storage disease characterized by accumulation of covalently unlinked (free) sialic acid in multiple tissues. ISSD and Salla disease (a predominantly neurological disorder) are allelic disorders caused by recessive mutations of a lysosomal anionic monosaccharide transporter, SLC17A5. While Salla disease is common in Finland due to a founder-effect mutation (p.Arg39Cys), ISSD is comparatively rare in all populations studied.Here, we describe the clinical and molecular features of two unrelated Canadian Inuit neonates with a virtually identical presentation of ISSD. Both individuals presented antenatally with fetal hydrops, dying shortly following delivery. Urinary free sialic acid excretion was markedly increased in the one case in which urine could be obtained for testing; postmortem examination showed a picture of widespread lysosomal storage in both. Both children were homozygous for a novel splice site mutation (NM_012434:c.526-2A>G) resulting in skipping of exon 4 and an ensuing frameshift. Analysis of a further 129 pan-Arctic Inuit controls demonstrated a heterozygous carrier rate of 1/129 (~0.4 %) in our sample. Interestingly, lysosomal enzyme studies showed an unexplained ninefold increase in neuraminidase activity, with lesser elevations in the activities of several other lysosomal enzymes. Our results raise the possibility of a common founder mutation presenting as hydrops in this population. Furthermore, if confirmed in subsequent cases, the marked induction of neuraminidase activity seen here may prove useful in the clinical diagnosis of ISSD.

Exome sequencing reveals a homozygous mutation in TWINKLE as the cause of multisystemic failure including renal tubulopathy in three siblings

Three deceased infants from a Pakistani consanguineous family presented with a similar phenotype of cholestatic liver disease, hypotonia, severe failure to thrive, recurrent vomiting, renal tubulopathy, and a progressive neurodegenerative course. Mitochondrial DNA depletion syndrome was considered in view of multisystem involvement. Exome sequencing, revealed a homozygous novel mutation c.1183T>C (p.F395L) in exon 1 of the C10orf2 TWINKLE gene. The hepatocerebral phenotype is well recognized in association with recessive mutations involving the C10orf2 TWINKLE gene. The feature of renal tubulopathy adds to the multisystemic presentation in our patients and further demonstrates an expansion of the phenotype in mitochondrial DNA depletion syndrome associated with TWINKLE gene mutations. The absence of features of an epileptic encephalopathy appears to be of added interest.

Severe phenotypic spectrum of mevalonate kinase deficiency with minimal mevalonic aciduria

Mevalonate kinase deficiency is a rare autosomal recessively inherited organic aciduria with a complex multi-systemic phenotype. We describe two deceased patients with clinically severe mevalonate kinase (MK) deficiency confirmed by MK mutation analysis. The phenotype in our patients ranged from neonatal hydrops in the first patient to severe failure to thrive, hepatosplenomegaly, recurrent febrile episodes and lymphadenopathy in the second. Both infants excreted relatively low amounts of mevalonic acid intermittently.

Coma, hyperammonemia, metabolic acidosis, and mutation: lessons learned in the acute management of late onset urea cycle disorders

Urea cycle disorders are an important and treatable cause of hyperammonemia in the newborn and pediatric age group. Presentation in adolescence or adult life is rare and can manifest as frequent vomiting and behavioral changes. An inherited metabolic disorder should be considered in adults with obvious or occult encephalopathy. Failure to diagnose and treat rapidly may lead to irreversible neuronal damage. An improved understanding of the diagnosis and management of late-onset urea cycle disorders is needed to assist nephrologists in providing optimal care. This report describes the clinical characteristics of a young man with first presentation of hyperammonemia in adult life.

Menkes disease and infantile epilepsy

OBJECTIVES

Menkes disease, an X linked recessive neurodegenerative disorder, results from a mutation in the gene coding for the copper transporting ATPase (ATP7A). Epilepsy is a major clinical feature of this disorder. We describe the clinical presentation, evolution of epilepsy and explore the biological underpinnings of epileptogenesis in Menkes disease.

METHODS

Longitudinal case study illustrating the natural history of epilepsy and results of subcutaneous cupric chloride supplementation in a patient with Menkes disease and literature review.

RESULTS

The onset and evolution of epilepsy in Menkes disease is marked by different stages. Early presentations typically involve focal seizures, with progression to epileptic spasms and a chronic late stage of epilepsy characterized by tonic seizures, myoclonic jerks, and multifocal epileptiform activity on the EEG. Morphological correlates in the brain include evidence of atrophy of grey matter, ventriculomegaly, tortuous intracranial vasculature, and white matter signal changes consistent with loss of myelin and axons. The presence of significant lactic acidosis in brain and cerebrospinal fluid suggests widespread disturbance in oxidative metabolism. Molecular consequences of the pathogenic ATP7A gene mutation lead to impairment in copper transport, which in turn causes deficiencies of key copper containing enzymes (dopamine β hydroxylase and cytochrome c oxidase). Microarray studies suggest widespread effects in dysregulation of genes involved in cellular responses to oxidative stress, ribosomal translation, signal transduction, mitochondrial function, and immune responses. Impairment of copper mediated NMDA receptor function further enhances neuronal excitability, excitotoxic neuronal injury, setting up a cascade that creates conditions for epileptogenesis to follow.

CONCLUSION

Neurological manifestations are likely related to perturbations in copper dependent enzymatic pathways involved in neurotransmitter and energy metabolism. Early diagnosis and institution of copper supplementation has been shown to be beneficial particularly in patients with residual ATP7A activity.

Transcriptional profiling of endocrine cerebro-osteodysplasia using microarray and next-generation sequencing

Background

Transcriptome profiling of patterns of RNA expression is a powerful approach to identify networks of genes that play a role in disease. To date, most mRNA profiling of tissues has been accomplished using microarrays, but next-generation sequencing can offer a richer and more comprehensive picture.

Methodology/Principal Findings

ECO is a rare multi-system developmental disorder caused by a homozygous mutation in ICK encoding intestinal cell kinase. We performed gene expression profiling using both cDNA microarrays and next-generation mRNA sequencing (mRNA-seq) of skin fibroblasts from ECO-affected subjects. We then validated a subset of differentially expressed transcripts identified by each method using quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Finally, we used gene ontology (GO) to identify critical pathways and processes that were abnormal according to each technical platform. Methodologically, mRNA-seq identifies a much larger number of differentially expressed genes with much better correlation to qRT-PCR results than the microarray (r² = 0.794 and 0.137, respectively). Biologically, cDNA microarray identified functional pathways focused on anatomical structure and development, while the mRNA-seq platform identified a higher proportion of genes involved in cell division and DNA replication pathways.

Conclusions/Significance

Transcriptome profiling with mRNA-seq had greater sensitivity, range and accuracy than the microarray. The two platforms generated different but complementary hypotheses for further evaluation.

A multiplex human syndrome implicates a key role for intestinal cell kinase in development of central nervous, skeletal, and endocrine systems

Six infants in an Old Order Amish pedigree were observed to be affected with endocrine-cerebro-osteodysplasia (ECO). ECO is a previously unidentified neonatal lethal recessive disorder with multiple anomalies involving the endocrine, cerebral, and skeletal systems. Autozygosity mapping and sequencing identified a previously unknown missense mutation, R272Q, in ICK, encoding intestinal cell kinase (ICK). Our results established that R272 is conserved across species and among ethnicities, and three-dimensional analysis of the protein structure suggests protein instability due to the R272Q mutation. We also demonstrate that the R272Q mutant fails to localize at the nucleus and has diminished kinase activity. These findings suggest that ICK plays a key role in the development of multiple organ systems.

Transcobalamin (TC) deficiency--potential cause of bone marrow failure in childhood

It is unusual for inborn errors of metabolism to be considered in the investigative work-up of pancytopenia. We report a family in which the proband presented with failure to thrive at 2 months of age and subsequent bone marrow failure. A previous sibling had died at 7 months of age with suspected leukaemia. Haematological findings in the proband were significant for pancytopenia, and bone marrow aspiration showed dysplastic changes in all cell lineages. Urinary organic acid analysis revealed elevated methylmalonic acid. The synthesis of transcobalamin II (transcobalamin, TC) by cultured fibroblasts was markedly reduced, confirming the diagnosis of TC deficiency. The proband and his younger asymptomatic sister (also found to have TC deficiency) were homozygous for R399X (c.1195C>T), a novel mutation resulting in the loss of the C- terminal 29 amino acids of TC, a highly conserved region. Response to parenteral vitamin B(12) in the proband was dramatic. At 6 years 3 months of age, physical examination is normal and developmental level is age appropriate. His sister is clinically asymptomatic and is also developing normally. Propionylcarnitine concentrations were not elevated in the newborn screening cards from the proband and sister, but that was for specimens retrieved from storage after 7 years and 5 years, respectively. Inherited and acquired cobalamin disorders should both be considered in the differential diagnosis of bone marrow failure syndromes in young children. Early detection of the metabolic causes of bone marrow failure can ensure prompt recovery in some cases involving the vitamin B(12) pathway.

Development of a clinical assay for detection of GAA mutations and characterization of the GAA mutation spectrum in a Canadian cohort of individuals with glycogen storage disease, type II

Glycogen storage disease, type II (GSDII; Pompe disease; acid maltase deficiency) is an autosomal recessive disease caused by mutations of the GAA gene that lead to deficient acid alpha-glucosidase enzyme activity and accumulation of lysosomal glycogen. Although measurement of acid alpha-glucosidase enzyme activity in fibroblasts remains the gold standard for the diagnosis of GSDII, analysis of the GAA gene allows confirmation of clinical or biochemical diagnoses and permits predictive and prenatal testing of individuals at risk of developing GSDII. We have developed a clinical molecular test for the detection of GAA mutations based on cycle sequencing of the complete coding region. GAA exons 2-20 are amplified in six independent PCR using intronic primers. The resulting products were purified and sequenced. Preliminary studies using this protocol were conducted with DNA from 21 GSDII-affected individuals from five centers across Canada. In total, 41 of 42 mutations were detected (96.7% detection rate). Mutations spanned intron 1 through exon 19 and included nine novel mutations. Haplotype analysis of recurrent mutations further suggested that three of these mutations are likely to have occurred independently at least twice. Additionally, we report the identification of the c.-32-13T>G GAA mutation in an individual with infantile variant GSDII, despite reports of this mutation being associated almost exclusively with late-onset forms of the disease. The development of a clinical molecular test provides an important tool for the management and counseling of families and individuals with GSDII, and has provided useful information about the GAA mutation spectrum in Canada.

Genetic characterization of two autosomal recessive disorders, Majewski-like and cerebral atrophy syndromes

Introduction: We recently identified two lethal recessive disorders segregating within the same Old Order Amish pedigree. The first disorder, Majewski-like syndrome (MLS), has features that overlap with both Majewski short rib-polydactyly syndrome and hydrolethalus syndrome. MLS is a lethal multi-system disorder that affects the development of the brain, adrenal glands, pituitary gland and bone. The second disorder, cerebral atrophy syndrome (CAS), is characterized by progressive and global loss of brain tissue. Affected children present early in life with microcephaly, seizures, and psychomotor retardation, and possess distinctive MRI findings. The objective of this study was to identify the genetic bases of these disorders to provide prompt and reliable diagnosis for families. Methods: Assuming recessive inheritance and mutation homogeneity (autozygosity), we used Affymetrix 10,000-single nucleotide polymorphism (10K-SNP) to genotype all affected individuals and identify candidate regions. SNP data were analyzed using Agilent GT autozygosity mapping software. LOD scores were used to identify candidate regions, and genes within these regions were prioritized for sequencing. Results and Conclusion: Because the Ontario Anabaptist population is relatively small, genetically isolated, and historically young, we were able to robustly map candidate regions using relatively low marker density and only a few affected individuals. Our preliminary data is consistent with the clinical observation that MLS and CAS segregate independently, as recessive conditions, within the pedigree. Thus far, we have sequenced 12 genes within the MLS locus, all of which were normal. For CAS, autozygosity mapping yielded two loci with comparable linkage scores, one of which contained no observable mutations. Once the causative mutations have been identified for MLS and CAS, we intend to study their population frequencies and also to pursue in vitro studies of gene and protein functions.

The cost-effectiveness of expanding newborn screening for up to 21 inherited metabolic disorders using tandem mass spectrometry: results from a decision-analytic model

OBJECTIVES

In 2005, in Ontario, Canada, newborns were only screened for phenylketonuria (PKU) and hypothyroidism. Tandem mass spectrometry (MS/MS) has since been implemented as a new screening technology because it can screen for PKU and many other diseases simultaneously. We estimated the cost-effectiveness of using this technology to expand the Ontario newborn screening program to screen for each disease independently and for hypothetical bundles of up to 21 metabolic diseases.

METHODS

We constructed a decision-analytic model to estimate the incremental costs and life-years of survival that can be gained by screening or changing screening technologies. Costs and health benefits were estimated for a cohort of babies born in Ontario in 1 year. Secondary sources and expert opinion were used to estimate the test characteristics, disease prevalence, treatment effectiveness, disease progression rates, and mortality. The London Health Sciences Centre Case Costing Initiative, the Ontario Health Insurance Plan Schedule, and the Ontario Drug Benefits plan formulary were used to estimate costs.

RESULTS

Changing screening technologies, from the Guthrie test to MS/MS, for PKU detection had an incremental cost of $5,500,000 per life-year (LY) gained. We identified no diseases for which the incremental cost of screening for just that disease was less than $100,000 per LY gained. The incremental costs of screening ranged from $222,000 (HMG-CoA lyase deficiency) to $142,500,000 (glutaric acidemia type II) per LY gained. Screening for a bundle of diseases including PKU and the 14 most cost-effective diseases to screen for cost less than $70,000 per LY gained, and the incremental cost-effectiveness of adding each of the 14 diseases to the bundle was less than $100,000 per LY gained. The incremental cost of adding the 15th most cost-effective disease was $309,400 per LY gained.

CONCLUSIONS

Early diagnosis and treatment of metabolic disease is important to reduce disease severity and delay or prevent the onset of the disease. Screening at birth reduces the morbidity, mortality, and social burden associated with the irreversible effects of disease on the population. Our analysis suggests that the cost-efficiencies gained by using MS/MS to screen for bundles of diseases rather than just one disease are sufficient to warrant consideration of an expanded screening program. It is, however, not cost-effective to screen for all diseases that can be screened for using this technology.

Fatal cerebral edema from late-onset ornithine transcarbamylase deficiency in a juvenile male patient receiving valproic acid

OBJECTIVES

The aims of this report are to 1) present a rare case of fatal cerebral edema associated with late-onset ornithine transcarbamylase (OTC) deficiency in a juvenile male patient receiving valproic acid and 2) review the neuropathologic changes associated with the hyperammonemia.

DESIGN

Case report.

SETTING

A community hospital and a tertiary pediatric critical care unit.

INTERVENTIONS

Carbohydrate administration, intravenous nitrogen excretion cocktail, and high-flux hemodialysis.

MEASUREMENTS AND MAIN RESULTS

Despite aggressive therapy for presumed late-onset OTC deficiency, the patient rapidly developed fatal cerebral edema with tonsillar herniation. A liver biopsy confirmed OTC deficiency with approximately 3% of residual hepatic enzyme activity. Chromosomal analysis showed a normal male karyotype. A thorough molecular analysis of the coding region in the OTC gene Xp21.1 was completed, but mutations were not identified, suggesting an upstream or downstream abnormality. Severe brain swelling was evident on neuropathology, and histopathology showed Alzheimer type II astrocytes, neuronal cytoplasmic changes, and hypertrophy and eosinophilia of the small arterial walls.

CONCLUSIONS

OTC deficiency is the most common urea cycle defect causing hyperammonemia. Late-onset presentations of OTC are infrequent, primarily affecting female patients. We present a rare case of a late-onset OTC deficiency in a juvenile male patient receiving valproic acid therapy who developed fatal cerebral edema. Valproic acid exacerbates acute elevations in ammonia and may contribute synergistically with ammonia to cerebral mitochondrial dysfunction.

Five novel mutations in the lysosomal sialidase gene (NEU1) in type II sialidosis patients and assessment of their impact on enzyme activity and intracellular targeting using adenovirus-mediated expression

Sialidosis is an autosomal recessive disease resulting from a deficiency of lysosomal sialidase. Type II sialidosis is a rare disease characterized clinically by hydrops fetalis, hepatosplenomegaly, and severe psychomotor retardation. Genomic DNA from four unrelated sialidosis patients was screened for mutations within the sialidase gene NEU1. Five novel mutations were identified. Four are missense and one is nonsense: c.674G>C (p.R225P), c.893C>T (p.A298V), c.3G>A (p.M1?), c.941C>G (p.R341G), and c.69G>A (p.W23X). We have used our findings and diagnostic tools to confirm the presence of a homozygous null allele in a neonate sibling. Recombinant adenoviruses expressing the mutant sialidase alleles in primary cell cultures were utilized to assess the impact of each mutation on enzyme activity and intracellular localization. None of the mutant alleles expressed significant enzymatic activity. The p.R341G mutation exerts its pathological effect by perturbing substrate binding, while the p.A298V and p.R225P mutations appear to impair the folding of the sialidase enzyme. Our findings point to mutation-sensitive amino acids involved in catalytic function or structural stability and indicate the potential utility of these mutations for molecular diagnosis of this rare disease.

Consequences of aging on mitochondrial respiratory chain enzymes in cultured human fibroblasts treated with ascorbate

The activities of mitochondrial respiratory chain enzymes with and without ascorbate pretreatment were assayed in 10- to 20-week-old cultures of human fibroblasts. Aging was associated with a significant loss of respiratory chain enzyme activities. The presence of ascorbate in the medium reduced the rate of loss of these enzymes. Free radical-mediated injuries may also contribute to aging since the changes seen in respiratory chain enzyme activities are similar to those seen in oxidatively stressed cells. This study demonstrates an age-related decline in mitochondrial respiratory chain activity as well as a protective role for ascorbate in aging.

Aspartylglucosaminuria in a Canadian family

Aspartylglucosaminuria (McKusick 208400) is a lysosomopathy associated with aspartylglucosaminidase (L-aspartamido-beta-N-acetylglucosamine amidohydrolase, EC 3.5.1.26) deficiency. It has been most frequently encountered in Finland, where the regional incidence may be as high as 1 in 3600 births. In North America it is very rare, having been reported in only 8 patients. We encountered 4 patients with aspartylglucosaminuria in a Canadian family of 12 siblings. The 4 siblings affected--2 brothers and 2 sisters--were apparently normal at birth; however, their developmental milestones, particularly speech, were slow, and they acquired only a simple vocabulary. Throughout life, there was a progressive coarsening of facial features; 3 had inguinal hernia and recurrent diarrhea; all became severely retarded and by the 4th decade showed evident deterioration of both cognitive and motor skills; 2 exhibited cyclical behavioural changes. Three of the siblings have died, at 33, 39 and 44 years of age. Two died of bronchopneumonia and 1 of asphyxiation following aspiration. In the urine of all 4 siblings, and in the 1 liver examined, we found 2-acetamido-1-N-(4-L-aspartyl)-2-deoxy-beta-D-glucosamine (GlcNAc-Asn) and alpha-D-mannose-(1,6)-beta-D-mannose-(1,4)-2-acetamido- 2-deoxy-beta-D-glucose-(1,4)-2-acetamido-1-N-(4-L-aspartyl)-2-deoxy-beta - D-glucosamine (Man2-GlcNAc2-Asn). Compared with the level of activity in controls, aspartylglucosaminidase activity was less than 2% in fibroblasts from 3 of the siblings, less than 0.5% in leukocytes from 1 sibling, and less than 1% in the liver of 1 sibling, whereas other acid hydrolase activities in these tissues were normal. Ultrastructural studies of skin showed that fibroblasts, endothelial cells and pericytes contained vacuoles with fine reticulo-floccular material. Glial and neuronal cells of the central nervous system showed similar inclusions as well as others composed of concentric or parallel membranous arrays intermingled with lipid droplets.

Isolated sulfite oxidase deficiency

Isolated sulfite oxidase (SO) deficiency is an autosomal recessively inherited inborn error of sulfur metabolism. In this report of a ninth patient the clinical history, laboratory results, neuropathological findings and a mutation in the sulfite oxidase gene are described. The data from this patient and previously published patients with isolated sulfite oxidase deficiency and molybdenum cofactor deficiency are summarized to characterize this rare disorder. The patient presented neonatally with intractable seizures and did not progress developmentally beyond the neonatal stage. Dislocated lenses were apparent at 2 months. There was increased urine excretion of sulfite and S-sulfocysteine and a decreased concentration of plasma cystine. A lactic acidemia was present for 6 months. Liver sulfite oxidase activity was not detectable but xanthine dehydrogenase activity was normal. The boy died of respiratory failure at 32 months. Neuropathological findings of cortical necrosis and extensive cavitating leukoencephalopathy were reminiscent of those seen in severe perinatal asphyxia suggesting an etiology of energy deficiency. A point mutation that resulted in a truncated protein missing the molybdenum-binding site has been identified.

Heteroallelic missense mutations of the galactosamine-6-sulfate sulfatase (GALNS) gene in a mild form of Morquio disease (MPS IVA)

Morquio disease (MPS IVA) is an autosomal recessive disorder caused by a deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS) activity. Patients commonly present in early infancy with growth failure, spondyloepiphyseal dysplasia, corneal opacification, and keratan sulfaturia, but milder forms have been described. We report on a patient who grew normally until age 5 years. Her keratan sulfaturia was not detected until adolescence, and she now has changes restricted largely to the axial skeleton. She has experienced only mildly impaired vision. At age 22, thin-layer chromatography of purified glycosaminoglycans showed some keratan sulfaturia. GALNS activity in fibroblast homogenate supernatants was 20 +/- 5% of controls (as compared to 5 +/- 3% of controls in severe MPS IVA, P < .003). Kinetic analysis of residual fibroblast GALNS activity in patient and parents revealed decreased K(m) and increased Vmax in the mother and daughter, but not in the father, compatible with compound heterozygosity. GALNS exons were amplified from patient genomic DNA and screened by SSCP. Two missense mutations, a C to T transition at position 335 (predicting R94C) and a T to G transversion at position 344 (predicting F97V), were found on sequencing an abnormally migrating exon 3 amplicon. Digestion of the amplicon with FokI and AccI restriction enzymes (specific for the R94C and F97V mutations, respectively) confirmed heterozygosity. In fibroblast transfection experiments, heterozygous R94C and F97V mutants independently expressed as severe and mild GALNS deficiency, respectively. We interpret these findings to indicate that our patient bears heteroallelic GALNS missense mutations, leading to GALNS deficiency and mild MPS IVA. Our findings expand the clinical and biochemical phenotype of MPS IVA, but full delineation of the genotype-phenotype relationship requires further study of native and transfected mutant cell lines.