[Show abstract][Hide abstract] ABSTRACT: Leigh syndrome (LS) is a rare heterogeneous progressive neurodegenerative disorder usually presenting in infancy or early childhood. Clinical presentation is variable and includes psychomotor delay or regression, acute neurological or acidotic episodes, hypotonia, ataxia, spasticity, movement disorders, and corresponding anomalies of the basal ganglia and brain stem on magnetic resonance imaging. To date, 35 genes have been associated with LS, mostly involved in mitochondrial respiratory chain function and encoded in either nuclear or mitochondrial DNA. We used whole-exome sequencing to identify disease-causing variants in four patients with basal ganglia abnormalities and clinical presentations consistent with LS. Compound heterozygote variants in ECHS1, encoding the enzyme enoyl-CoA hydratase were identified. One missense variant (p.Thr180Ala) was common to all four patients and the haplotype surrounding this variant was also shared, suggesting a common ancestor of French-Canadian origin. Rare mutations in ECHS1 as well as in HIBCH, the enzyme downstream in the valine degradation pathway, have been associated with LS or LS-like disorders. A clear clinical overlap is observed between our patients and the reported cases with ECHS1 or HIBCH deficiency. The main clinical features observed in our cohort are T2-hyperintense signal in the globus pallidus and putamen, failure to thrive, developmental delay or regression, and nystagmus. Respiratory chain studies are not strikingly abnormal in our patients: one patient had a mild reduction of complex I and III and another of complex IV. The identification of four additional patients with mutations in ECHS1 highlights the emerging importance of this pathway in LS.
Human Genetics 06/2015; 134(9). DOI:10.1007/s00439-015-1577-y · 4.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Deficiency of pyridox(am)ine 5'-phosphate oxidase (PNPO, OMIM 610090) is a treatable autosomal recessive inborn error of metabolism. Neonatal epileptic encephalopathy and a low cerebrospinal fluid (CSF) pyridoxal 5'-phosphate level are the reported hallmarks of PNPO deficiency, but its clinical and biochemical spectra are not fully known.
A girl born at 33 3/7 weeks of gestation developed seizures in the first hours of life. Her seizures initially responded to GABAergic agonists, but she subsequently developed a severe epileptic encephalopathy. Brain MRI and infectious and metabolic evaluations at birth, including urinary alpha-aminoadipic semialdehyde (AASA), were normal. Lumbar puncture at age 3 months showed: pyridoxal 5'-phosphate, 52 nmol/L (normal, 23-64); homovanillic acid, 392 nmol/L (normal, 450-1,132); 5-hydroxyindoleacetic acid, 341 nmol/L (normal, 179-711); and 3-ortho-methyldopa, 30 nmol/L (normal, below 300). The patient was not being treated with pyridoxine nor with pyridoxal 5'-phosphate at the time of the lumbar puncture. She died at age 14 months. A sequencing panel targeting 53 epilepsy-related genes revealed a homozygous missense mutation in PNPO (c.674G>A, p.R225H). Homozygosity was confirmed by parental testing. Expression studies of mutant p.R225H PNPO revealed greatly reduced activity. In conclusion, a normal CSF level of pyridoxal 5'-phosphate does not rule out PNPO deficiency.
[Show abstract][Hide abstract] ABSTRACT: KIF1A is a neuron specific motor protein that plays important roles in cargo transport along neurites. Recessive mutations in KIF1A were previously described in families with spastic paraparesis or sensory and autonomic neuropathy type-2. Here, we report 11 heterozygous de novo missense mutations (p.S58L, p.T99M, p.G102D, p.V144F, p.R167C, p.A202P, p.S215R, p.R216P, p.L249Q, p.E253K, p.R316W) in KIF1A in 14 individuals, including two monozygotic twins. Two mutations (p.T99M and p.E253K) were recurrent, each being found in unrelated cases. All these de novo mutations are located in the motor domain of KIF1A. Structural modeling revealed that they alter conserved residues that are critical for the structure and function of the motor domain. Transfection studies suggested that at least five of these mutations affect the transport of the motor domain along axons. Individuals with de novo mutations in KIF1A display a phenotype characterized by cognitive impairment and variable presence of cerebellar atrophy, spastic paraparesis, optic nerve atrophy, and peripheral neuropathy, and epilepsy. Our findings thus indicate that de novo missense mutations in the motor domain of KIF1A cause a phenotype that overlaps with, while being more severe, than that associated with recessive mutations in the same gene. This article is protected by copyright. All rights reserved.
Human Mutation 01/2015; 36(1). DOI:10.1002/humu.22709 · 5.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS) is characterized by marked dilatation of the bladder and microcolon and decreased intestinal peristalsis. Recent studies indicate that heterozygous variants in ACTG2, which codes for a smooth muscle actin, cause MMIHS. However, such variants do not explain MMIHS cases that show an autosomal recessive mode of inheritance. We performed exome sequencing in a newborn with MMIHS and prune belly phenotype whose parents are consanguineous and identified a homozygous variant (c.3598A>T: p.Lys1200Ter) in MYH11, which codes for the smooth muscle myosin heavy chain. Previous studies showed that loss of Myh11 function in mice causes a bladder and intestinal phenotype that is highly reminiscent of MMIHS. All together, these observations strongly suggest that loss-of-function variants in MYH11 cause MMIHS. The documentation of variants in ACTG2 and MYH11 thus points to the involvement of the contractile apparatus of the smooth muscle in MMIHS. Interestingly, dominant-negative variants in MYH11 have previously been shown to cause thoracic aortic aneurism and dilatation. Different mechanisms of MYH11 disruption may thus lead to distinct patterns of smooth muscle dysfunction.European Journal of Human Genetics advance online publication, 19 November 2014; doi:10.1038/ejhg.2014.256.
European journal of human genetics: EJHG 11/2014; 23(9). DOI:10.1038/ejhg.2014.256 · 4.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Triglyceride (TG) synthesis, storage, and degradation together constitute cytoplasmic TG metabolism (CTGM). CTGM is mostly studied in adipocytes, where starting from glycerol-3-phosphate and fatty acyl (FA)-coenzyme A (CoA), TGs are synthesized then stored in cytoplasmic lipid droplets. TG hydrolysis proceeds sequentially, producing FAs and glycerol. Several reactions of CTGM can be catalyzed by more than one enzyme, creating great potential for complex tissue-specific physiology. In adipose tissue, CTGM provides FA as a systemic energy source during fasting and is related to obesity. Inborn errors and mouse models have demonstrated the importance of CTGM for non-adipose tissues, including skeletal muscle, myocardium and liver, because steatosis and dysfunction can occur. We discuss known inborn errors of CTGM, including deficiencies of: AGPAT2 (a form of generalized lipodystrophy), LPIN1 (childhood rhabdomyolysis), LPIN2 (an inflammatory condition, Majeed syndrome, described elsewhere in this issue), DGAT1 (protein loosing enteropathy), perilipin 1 (partial lipodystrophy), CGI-58 (gene ABHD5, neutral lipid storage disease (NLSD) with ichthyosis and "Jordan's anomaly" of vacuolated polymorphonuclear leukocytes), adipose triglyceride lipase (ATGL, gene PNPLA2, NLSD with myopathy, cardiomyopathy and Jordan's anomaly), hormone-sensitive lipase (HSL, gene LIPE, hypertriglyceridemia, and insulin resistance). Two inborn errors of glycerol metabolism are known: glycerol kinase (GK, causing pseudohypertriglyceridemia) and glycerol-3-phosphate dehydrogenase (GPD1, childhood hepatic steatosis). Mouse models often resemble human phenotypes but may diverge markedly. Inborn errors have been described for less than one-third of CTGM enzymes, and new phenotypes may yet be identified.
[Show abstract][Hide abstract] ABSTRACT: In male mice, deficiency of hormone sensitive lipase (HSL, Lipe gene, E.C.126.96.36.199) causes deficient spermatogenesis, azoospermia and infertility. Postmeiotic germ cells express a specific HSL isoform that includes a 313 amino acid N-terminus encoded by a testis-specific exon (exon T1). The remainder of testicular HSL is identical to adipocyte HSL. The amino acid sequence of the testis-specific exon is poorly conserved, showing only a 46 amino acid identity with orthologous human and rat sequences, compared with 87% over the remainder of the HSL coding sequence, providing no evidence in favor of a vital functional role for the testis-specific N-terminus of HSL. However, exon T1 is important for Lipe transcription: in mouse testicular mRNA, we identified 3 major Lipe transcription start sites, finding numerous testicular transcription factor binding motifs upstream of the transcription start site. We directly explored two possible mechanisms for the infertility of HSL-deficient mice, using mice that expressed mutant HSL transgenes only in postmeiotic germ cells, on a HSL-deficient background. One transgene expressed human HSL lacking enzyme activity but containing the testis-specific N-terminus (HSL-/-muttg mice). The other transgene expressed catalytically-inactive HSL with the testis-specific N-terminal peptide (HSL-/-atg mice). HSL-/-muttg mice were infertile, with abnormal histology of the seminiferous epithelium and absence of spermatozoa in the epididymal lumen. In contrast, HSL-/-atg mice had normal fertility and normal testicular morphology. In conclusion, while the catalytic function of HSL is necessary for spermatogenesis in mice, the presence of the N-terminal testis-specific fragment is not essential.
[Show abstract][Hide abstract] ABSTRACT: We analyzed four families that presented with a similar condition characterized by congenital microcephaly, intellectual disability, progressive cerebral atrophy, and intractable seizures. We show that recessive mutations in the ASNS gene are responsible for this syndrome. Two of the identified missense mutations dramatically reduce ASNS protein abundance, suggesting that the mutations cause loss of function. Hypomorphic Asns mutant mice have structural brain abnormalities, including enlarged ventricles and reduced cortical thickness, and show deficits in learning and memory mimicking aspects of the patient phenotype. ASNS encodes asparagine synthetase, which catalyzes the synthesis of asparagine from glutamine and aspartate. The neurological impairment resulting from ASNS deficiency may be explained by asparagine depletion in the brain or by accumulation of aspartate/glutamate leading to enhanced excitability and neuronal damage. Our study thus indicates that asparagine synthesis is essential for the development and function of the brain but not for that of other organs.
[Show abstract][Hide abstract] ABSTRACT: To describe the long-term ophthalmologic outcomes of patients with methylmalonic aciduria and homocystinuria, cobalamin C type (cblC).
Retrospective case series.
All patients with cblC referred to the Department of Ophthalmology of the Centre Hospitalier Universitaire Sainte-Justine from 1984 through 2012 were studied. Twelve such patients were identified.
Clinical ophthalmic examinations, neuroimaging, electroretinography, and the results of MMACHC mutation analysis were reviewed retrospectively.
We examined visual acuity, ocular alignment, presence of maculopathy and peripheral retinopathy, optic atrophy, and nystagmus. Photopic and scotopic electroretinograms were reviewed. We examined and compared mutations in the MMACHC gene. Neuroimaging abnormalities were compiled when available.
Twelve cblC patients were followed up from 2 to 23 years (average, 10 years). Eleven of 12 patients were diagnosed before the age of 1 year (range, birth-2 years). An initial ophthalmic examination was performed within the first year of age in 9 of 12 patients. Visual acuity at the time of presentation was variable, ranging from light perception to 20/20. Visual acuity was worse than 20/100 in 75% (9/12) of patients at last follow-up. Eight patients (67%) had obvious maculopathy on fundus examination. Other findings included peripheral retinopathy (8/12 [67%]), nystagmus (8/12 [67%]), strabismus (5/12 [42%]), and optic atrophy (6/12 [50%]). Funduscopic deterioration was documented in 1 patient, whereas electrophysiologic changes occurred in 4 patients. Neuroimaging results were available in 7 of the patients, revealing corpus callosum atrophy (7/7 [100%]) and periventricular white matter loss (6/7 [85%]).
Most children in our series had early-onset disease with neurologic manifestations and abnormal ophthalmologic examination results. Despite early treatment, many early-onset cblC patients have poor visual function.
The author(s) have no proprietary or commercial interest in any materials discussed in this article.
[Show abstract][Hide abstract] ABSTRACT: The scavenger receptor CD36 plays a central role in lipid metabolism by promoting macrophage cholesterol efflux with the potential to reduce atherosclerotic lesions. However, the effect of CD36 on de novo cholesterol synthesis is not known. Here, we describe the cellular mechanism by which CD36 activation induces cholesterol depletion in HepG2 cells. Using the CD36 ligand hexarelin, we found a rapid phosphorylation of HMG-CoA reductase Ser-872 in treated cells, resulting in inactivation of the rate-limiting enzyme in sterol synthesis. Degradation of HMG-CoA reductase by the ubiquitin-proteasome pathway was also enhanced by hexarelin, through an increased recruitment of the anchor proteins insulin-induced gene (Insig)-1 and Insig-2. Genes encoding key enzymes involved in cholesterol synthesis and under the control of transcription factor sterol regulatory element-binding protein (SREBP)-2 remained unresponsive to sterol depletion, due to retention of the SREBP-2 escort protein Scap by Insig-1/2. Insig1 and Insig2 gene expression was also increased through activation of nuclear receptor peroxisome-proliferator activating receptor γ (PPARγ) by CD36, which lifted the inhibitory effect of PPARγ1 Ser-84 phosphorylation. Recruitment of coactivator peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) to activated AMPKα was also promoted, resulting in PGC-1α transcriptional activation through Sirt1-mediated deacetylation, increased recruitment of PPARγ, and up-regulation of Insig-1/2, revealing a regulatory role of CD36 on PGC-1α signaling. Our data identify CD36 as a novel regulator of HMG-CoA reductase function and Insig-1/2 expression, 2 critical steps regulating cholesterol synthesis in hepatocytes.-Rodrigue-Way, A., Caron, V., Bilodeau, S., Keil, S., Hassan, M., Lévy, E., Mitchell. G. A., Tremblay, A. Scavenger receptor CD36 mediates inhibition of cholesterol synthesis via activation of the PPARγ/PGC-1α pathway and Insig1/2 expression in hepatocytes.
Canadian Journal of Diabetes 10/2013; 37S4(4):S65. DOI:10.1016/j.jcjd.2013.08.196 · 2.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Most conditions detected by expanded newborn screening result from deficiency of one of the enzymes that degrade acyl-coenzyme A (CoA) esters in mitochondria. The role of acyl-CoAs in the pathophysiology of these disorders is poorly understood, in part because CoA esters are intracellular and samples are not generally available from human patients. We created a mouse model of one such condition, deficiency of 3-hydroxy-3-methylglutaryl-CoA lyase (HL), in liver (HLLKO mice). HL catalyses a reaction of ketone body synthesis and of leucine degradation. Chronic HL deficiency and acute crises each produced distinct abnormal liver acyl-CoA patterns, which would not be predictable from levels of urine organic acids and plasma acylcarnitines. In HLLKO hepatocytes, ketogenesis was undetectable. Carboxylation of [2-(14)C] pyruvate diminished following incubation of HLLKO hepatocytes with the leucine metabolite 2-ketoisocaproate (KIC). HLLKO mice also had suppression of the normal hyperglycemic response to a systemic pyruvate load, a measure of gluconeogenesis. Hyperammonemia and hypoglycemia, cardinal features of many inborn errors of acyl-CoA metabolism, occurred spontaneously in some HLLKO mice and were inducible by administering KIC. KIC loading also increased levels of several leucine-related acyl-CoAs and reduced acetyl-CoA levels. Ultrastructurally, hepatocyte mitochondria of KIC-treated HLLKO mice show marked swelling. KIC-induced hyperammonemia improved following administration of carglumate (N-carbamyl-L-glutamic acid), which substitutes for the product of an acetyl-CoA-dependent reaction essential for urea cycle function, demonstrating an acyl-CoA-related mechanism for this complication.
PLoS ONE 07/2013; 8(7):e60581. DOI:10.1371/journal.pone.0060581 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mucopolysaccharidosis IVA (MPS IVA) is caused by deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS), leading to systemic skeletal dysplasia because of excessive storage of keratan sulfate (KS) in chondrocytes. In an effort to determine a precise prognosis and personalized treatment, we aim to characterize clinical, biochemical, and molecular findings in MPS IVA patients, and to seek correlations between genotype, phenotype, and blood and urine KS levels. Mutation screening of GALNS gene was performed in 55 MPS IVA patients (severe: 36, attenuated: 13, undefined: 6) by genomic PCR followed by direct sequence analysis. Plasma and urine KS levels were measured by ELISA method. Genotype/phenotype/KS correlations were assessed when data were available. Fifty-three different mutations including 19 novel ones (41 missense, 2 nonsense, 4 small deletions, 1 insertion, and 5 splice-site) were identified in 55 patients and accounted for 93.6% of the analyzed mutant alleles. Thirty-nine mutations were associated with a severe phenotype and ten mutations with an attenuated one. Blood and urine KS concentrations in MPS IVA patients were age-dependent and markedly higher than those in age-matched normal controls. Plasma and urine KS levels in MPS IVA patients with the severe phenotype were higher than in those with an attenuated form. This study provides evidence for extensive allelic heterogeneity of MPS IVA. Accumulation of mutations as well as clinical descriptions and KS levels allows us to predict clinical severity more precisely and should be used for evaluation of responses to potential treatment options.
[Show abstract][Hide abstract] ABSTRACT: Neuraminidases (sialidases) catalyze the removal of sialic acid residues from sialylated glycoconjugates. We now report that mammalian neuraminidase 1 (Neu1), in addition to its catabolic function in lysosomes, is transported to the cell surface where it is involved in regulation of insulin signaling. Insulin binding to its receptor rapidly induces interaction of the receptor with Neu1, which hydrolyzes sialic acid residues in the glycan chains of the receptor and, consequently, induces its activation. Cells from sialidosis patients with a genetic deficiency of Neu1 show impairment of insulin-induced phosphorylation of downstream protein kinase AKT, while treatment of these cells with purified Neu1 restores signaling. Genetically-modified mice with ∼10% of the normal Neu1 activity exposed to a high-fat diet develop hyperglycemia and insulin resistance twice as fast as their wild type counterparts. Together, these studies identify Neu1 as a novel component of the signaling pathways of energy metabolism and glucose uptake.
[Show abstract][Hide abstract] ABSTRACT: Unlabelled:
Carboxylesterase 3/triacylglycerol hydrolase (Ces3/TGH) participates in hepatic very low-density lipoprotein (VLDL) assembly and in adipose tissue basal lipolysis. Global ablation of Ces3/Tgh expression decreases serum triacylglycerol (TG) and nonesterified fatty acid levels and improves insulin sensitivity. To understand the tissue-specific role of Ces3/TGH in lipid and glucose homeostasis, we generated mice with a liver-specific deletion of Ces3/Tgh expression (L-TGH knockout [KO]). Elimination of hepatic Ces3/Tgh expression dramatically decreased plasma VLDL TG and VLDL cholesterol concentrations but only moderately increased liver TG levels in mice fed a standard chow diet. Significantly reduced plasma TG and cholesterol without hepatic steatosis were also observed in L-TGH KO mice challenged with a high-fat, high-cholesterol diet. L-TGH KO mice presented with increased plasma ketone bodies and hepatic fatty acid oxidation. Intrahepatic TG in L-TGH KO mice was stored in significantly smaller lipid droplets. Augmented hepatic TG levels in chow-fed L-TGH KO mice did not affect glucose tolerance or glucose production from hepatocytes, but impaired insulin tolerance was observed in female mice.
Our data suggest that ablation of hepatic Ces3/Tgh expression decreases plasma lipid levels without causing severe hepatic steatosis.