HMG CoA lyase deficiency: identification of five causal point mutations in codons 41 and 42, including a frequent Saudi Arabian mutation, R41Q

HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMG-CoA lyase) is a rare inborn error of leucine degradation and ketone body synthesis, caused by homozygous or compound heterozygous disease-causing variants in HMGCL. To understand the natural history of this disease, we reviewed the biochemical, clinical, and molecular data of 62 patients from 54 different families with confirmed HMG-CoA lyase deficiency (HMGCLD) diagnosis from Saudi Arabia. The majority of the affected individuals were symptomatic. At initial diagnosis, 38 patients (61.29%) presented with hypoglycemia and 49 patients (79.03%) developed metabolic acidosis. In 27 patients (43.54%), the disorder manifested in the neonatal period, mostly within the first days of life, while 35 (56.45%) patients were diagnosed within the first year of life or beyond. All the patients were alive and developed long-term neurological complications during data collection, which may significantly influence their quality of life. Common neurological findings include seizures 17/62 (27.41%), hypotonic 3/62 (4.83%), speech delay 7/62 (11.29%), hyperactivity 4/62 (4.83%), developmental delay 6/62 (9.677%), learning disability 15/62 (24.14%), and ataxic gate 1/62 (1.612%). An MRI of the brain exhibited nonspecific periventricular and deep white matter hyperintense signal changes in 16 patients (25.80%) and cerebral atrophy was found in one (1/62; 1.612%) patient. We identified a founder variant [c.122G>A; p.(Arg41Gln)] in 48 affected individuals (77.41%) in the HMGCL gene. This is the largest cohort of HMGCLD patients reported from Saudi Arabia, signifying this disorder as a likely life-threatening disease, with a high prevalence in the region. Our findings suggest that diagnosis at an early stage with careful dietary management may avoid metabolic crises.

Hepatic Manifestations of 3-Hydroxy-3-Methylglutaryl-Coenzyme-A Lyase Deficiency in Saudi Patients: Experience of a Tertiary Care Center

3-Hydroxy-3-methylglutaryl-coenzyme-A lyase (HMGCL) deficiency, a rare autosomal recessive disorder, is caused by a homozygous or compound heterozygous mutation in the HMGCL gene (chromosome 1p36.11). HMGCL catalyzes the final step of leucine degradation and plays a key role in ketone body formation. Several studies have reported general hepatic findings (e.g., hepatomegaly) in patients with HMGCL deficiency, but currently, there are no available data regarding the incidence and epidemiology of liver involvement. The main objective of our study was to investigate the overall clinical manifestations, laboratory findings, genotype, and presence of hepatic involvement in Saudi patients with HMGCL deficiency. A retrospective chart review of patients with HMGCL deficiency including those with a documented hepatic manifestation was performed at the King Faisal Specialist Hospital & Research Centre in Riyadh, Saudi Arabia. We evaluated 50 cases of HMGCL deficiency. Hepatic findings were found in 17 patients at the time of diagnosis. The mean age of hepatic presentation was 135 days, and the median age was 56 days (range: 2-315 days). Hepatomegaly was found in 65%, abnormal biochemical profile in 47%, and an abnormal imaging in 53% of patients. The most frequent mutation in this cohort was the p.Arg41Gln founder mutation (59%). In comparison to data from the current literature, HMGCL deficiency can be considered as a diagnostic metabolite for hepatic manifestations and requires appropriate evaluation, including molecular genetic analysis.

Genomewide association analysis of sow lactation performance traits in lines of Yorkshire pigs divergently selected for residual feed intake during grow-finish phase

Lactation is an economically and biologically important phase in the life cycle of sows. Short generation intervals in nucleus herds and low heritability of traits associated with lactation along with challenges associated with collecting accurate lactation performance phenotypes emphasize the importance of using genomic tools to examine the underlying genetics of these traits. We report the first genomewide association study (GWAS) on traits associated with lactation and efficiency in 2 lines of Yorkshire pigs that were divergently selected for residual feed intake during grow-finish phase. A total of 862 farrowing records from 2 parities were analyzed using a Bayesian whole genome variable selection model (Bayes B) to locate 1-Mb regions that were most strongly associated with each trait. The GWAS was conducted separately for parity 1 and 2 records. Marker-based heritabilities ranged from 0.03 to 0.39 for parity 1 traits and from 0.06 to 0.40 for parity 2 traits. For all traits studied, around 90% of genetic variance came from a large number of genomic regions with small effects, whereas genomic regions with large effects were found to be different for the same trait measured in parity 1 and 2. The highest percentage of genetic variance explained by a 1-Mb window for each trait ranged from 0.4% for feed intake during lactation to 4.2% for back fat measured at farrowing in parity 1 sows and from 0.2% for lactation feed intake to 5.4% for protein mass loss during lactation in parity 2 sows. A total of thirteen 1-Mb nonoverlapping windows were found to explain more than 1.5% of genetic variance for either a single trait or across multiple traits. These 1-Mb windows were on chromosomes 2, 3, 6, 7, 8, 11, 14, 15, 17, and 18. The major positional candidate genes within 1 Mb upstream and downstream of these windows were , (SSC2), (SSC6) (SSC7), (SSC8), (SSC11), (SSC14), (SSC17). Further validation studies on larger populations are required to validate these findings and to improve our understanding of the biology and complex genetic architecture of traits associated with sow lactation performance.

Characterization of a novel HMG-CoA lyase enzyme with a dual location in endoplasmic reticulum and cytosol

A novel lyase activity enzyme is characterized for the first time: HMG-CoA lyase-like1 (er-cHL), which is a close homolog of mitochondrial HMG-CoA lyase (mHL). Initial data show that there are nine mature transcripts for the novel gene HMGCLL1, although none of them has all its exons. The most abundant transcript is called “variant b,” and it lacks exons 2 and 3. Moreover, a three-dimensional model of the novel enzyme is proposed. Colocalization studies show a dual location of the er-cHL in the endoplasmic reticulum (ER) and cytosol, but not in mitochondria or peroxisomes. Furthermore, the dissociation experiment suggests that it is a nonendoplasmic reticulum integral membrane protein. The kinetic parameters of er-cHL indicate that it has a lower V_max and a higher substrate affinity than mHL. Protein expression and lyase activity were found in several tissues, and were particularly strong in lung and kidney. The occurrence of er-cHL in brain is surprising, as mHL has not been found there. Although mHL activity is clearly associated with energy metabolism, the results suggest that er-cHL is more closely related to another metabolic function, mostly at the pulmonary and brain level.

Influence of multiple cysteines on human 3-hydroxy-3-methylglutaryl-CoA lyase activity and formation of inter-subunit adducts

Human 3-hydroxy-3-methylglutaryl-CoA lyase catalyzes formation of acetyl-CoA and acetoacetate in a reaction that requires divalent cation and is stimulated by sulfhydryl protective reagents. The enzyme is a homodimer and inter-subunit adducts form in the absence of reducing agents or upon treatment with cysteine selective crosslinking agents. To address the influence of cysteines on enzyme activity and formation of inter-subunit and intra-subunit adducts, single serine substitutions have been engineered for each enzyme cysteine. Enzyme activity varies for each cysteine→serine mutant protein and different mutations have widely different effects on recovery of activity upon DTT treatment of non-reduced enzyme. These levels of enzyme activity do not strongly correlate with formation of inter-subunit adducts by these HMGCL mutants. C170S, C266S, and C323S proteins do not form inter-subunit disulfide adducts but such an adduct is restored in the C170S/C174S double mutant. Coexpression of HMGCL proteins encoded by C266S and C323S expression plasmids supports formation of a C266S/C323S heterodimer which does form a covalent inter-subunit adduct. These observations are interpreted in the context of competition between cysteines in formation of intra-subunit and inter-subunit heterodisulfide adducts.

Incidence of 3-hydroxy-3-methylglutaryl-coenzyme A lyase (HL) deficiency in Brazil, South America

3-Hydroxy-3-methylglutaryl-CoA lyase (HL) deficiency (3-hydroxy-3-methylglutaric aciduria, 3-HMG) is a rare autosomal recessive inborn error of metabolism involving the final step of leucine degradation. HL is the key enzyme for the production of glucose-sparing ketone bodies for brain. Positive biochemical findings are metabolic acidosis, hyperammonaemia, and hypoketotic hypoglycaemia in the neonatal period or infancy. In the present study we report 15 Brazilian patients with HL deficiency and present their clinical and biochemical findings. Urine from all patients contained large amounts of 3-hydroxy-3-methylglutaric, 3-methylglutaconic, 3-hydroxyisovaleric and 3-methylglutaric acids, and 3-methylcrotonylglycine was also observed in 13 patients. The main features at clinical presentation were hypoglycaemia (12 patients), seizures (10 patients), metabolic acidosis (9 patients), vomiting (6 patients), and hepatomegaly (5 patients). All but two patients were of Portuguese ancestry. HL deficiency comprised 7.3% of total organic acidurias detected in our laboratory during a 13-year time span, indicating a high incidence of this disorder in Brazil. Limited molecular characterization (4/15 patients only) revealed two mutations common for individuals of Portuguese/Spanish (Iberian Peninsula) ancestry (E37X and V168fs(-2)). Our findings increase the number of HL-deficient patients and reinforce the characteristic phenotypic picture of the disease. Effective dietary interventions based on mild protein restriction and avoidance of fasting and possibly alternative C5 ketone body generating therapy for this disorder may provide further impetus and rationale for expanded newborn screening of HL deficiency.

Evaluation of diagnostic fasting in the investigation of hypoglycemia in children omani experienc

OBJECTIVES

To assess the safety and importance of diagnostic fast in the evaluation of hypoglycemia in children in a non-specialist set up.

METHOD

The medical records of 116 patients with hypoglycemia, admitted to Pediatric Unit, Royal Hospital, Muscat, Sultanate of Oman, over a 15 year period, were reviewed. Of these, 96 (82.8%) patients, 52 boys and 44 girls, aged 8 days to 10 years were subjected to diagnostic fast.

RESULTS

Of these 96 patients fasted, 77 (80.2%) became hypoglycemic (HG group) and 19 (19.8 %) did not develop hypoglycemia on fast (NHG group). In the HG group, 69 (89.6%) patients developed symptomatic hypoglycemia of variable severity and none developed coma or convulsions during fasting.

CONCLUSION

The study has proved that diagnostic fast is relatively a safe procedure with considerable amount of diagnostic yield.

3-Hydroxy-3-methylglutaryl coenzyme a lyase deficiency with reversible white matter changes after treatment

We report the case of an 8-month-old infant with 3-hydroxy-3-methylglutaryl coenzyme A deficiency (OMIM 246450), an inborn error of leucine catabolism and ketogenesis, who presented with nonketotic hypoglycemia and seizures. He demonstrated reversible white matter changes on serial brain magnetic resonance imaging, together with clinical normalization, after initiation of a leucine-restricted diet.

C-terminal end and aminoacid Lys48 in HMG-CoA lyase are involved in substrate binding and enzyme activity

3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) lyase adopts a (betaalpha)(8) TIM barrel structure with an additional beta9, alpha11 and alpha12 helices. Location of HMG part of the substrate has been suggested but the binding mode for the CoA moiety remains to be resolved. As mutation F305 fs(-2), which involves the last 21 residues of the protein, and mutation K48N caused 3-hydroxy-3-methylglutaric aciduria in two patients, we examined the role of the C-terminal end and Lys(48) in enzyme activity. Expression studies of various C-terminal-end-deleted and K48N-mutated proteins revealed that residues 311-313 (localized in the loop between alpha11 and alpha12 helices) and Lys(48) are essential for enzyme activity. An in silico docking model locating HMG-CoA on the surface of the enzyme implicates Asn(311) and Lys(313) in substrate binding by establishing multiple polar contacts with phosphate and ribose groups of adenosine, and Lys(48) by contacting the carboxyl group of the panthotenic acid moiety.

Mutations underlying 3-hydroxy-3-methylglutaryl CoA lyase deficiency in the Saudi population

BACKGROUND

3-hydroxy-3-methylglutaric aciduria (3HMG, McKusick: 246450) is an autosomal recessive branched chain organic aciduria caused by deficiency of the enzyme 3-Hydroxy-3-Methylglutaryl CoA lyase (HL, HMGCL, EC 4.1.3.4). HL is encoded by HMGCL gene and many mutations have been reported. 3HMG is commonly observed in Saudi Arabia.

METHODS

We utilized Whole Genome Amplification (WGA), PCR and direct sequencing to identify mutations underlying 3HMG in the Saudi population. Two patients from two unrelated families and thirty-four 3HMG positive dried blood spots (DBS) were included.

RESULTS

We detected the common missense mutation R41Q in 89% of the tested alleles (64 alleles). 2 alleles carried the frame shift mutation F305fs (-2) and the last two alleles had a novel splice site donor IVS6+1G>A mutation which was confirmed by its absence in more than 100 chromosomes from the normal population. All mutations were present in a homozygous state, reflecting extensive consanguinity. The high frequency of R41Q is consistent with a founder effect. Together the three mutations described account for >94% of the pathogenic mutations underlying 3HMG in Saudi Arabia.

CONCLUSION

Our study provides the most extensive genotype analysis on 3HMG patients from Saudi Arabia. Our findings have direct implications on rapid molecular diagnosis, prenatal and pre-implantation diagnosis and population based prevention programs directed towards 3HMG.

Corticospinal tract involvement in a patient with 3-HMG coenzyme A lyase deficiency

3-Hydroxy-3-methylglutaryl coenzyme A lyase deficiency, an inborn error of ketone body synthesis and leucine degradation, is a rare disorder. There are few reports demonstrating clinical and neuroradiologic findings of this condition. This report describes a 3.5-year-old previously healthy male who was admitted with complex partial seizures and was diagnosed as having 3-hydroxy-3-methylglutaryl coenzyme A lyase deficiency. The patient's previous medical history was unremarkable. His development and neurologic examination were normal. Cranial magnetic resonance imaging indicated prominent corticospinal tract and pontine involvement with focal cerebral white matter changes which have not been described in the literature before.

A single-residue mutation, G203E, causes 3-hydroxy-3-methylglutaric aciduria by occluding the substrate channel in the 3D structural model of HMG-CoA lyase

3-Hydroxy-3-methylglutaric aciduria is a rare autosomal recessive genetic disorder that affects ketogenesis and leucine metabolism. The disease is caused by mutations in the gene coding for 3-hydroxy-3-methylglutaryl-coenzyme A lyase (HL). To date 26 different mutations have been described. A (betaalpha)(8) TIM barrel structure has been proposed for the protein, and almost all missense mutations identified so far localize in the beta sheets that define the inside cavity. We report an Italian patient who bears homozygously a novel HL mutation, c.608G > A (p. G203E) in beta sheet six. A structural model of the mutated protein suggests that glutamic acid 203 impedes catalysis by blocking the entrance to the inner cavity of the enzyme. Loss of functionality has been confirmed in expression studies in E. coli, which demonstrate that the G203E mutation completely abolishes enzyme activity. Beta sheet six and beta sheet two are the two protein regions that accumulate most missense mutations, indicating their importance in enzyme functionality. A model for the mechanism of enzyme function is proposed.

Crystal structure of human 3-hydroxy-3-methylglutaryl-CoA Lyase: insights into catalysis and the molecular basis for hydroxymethylglutaric aciduria

3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) lyase is a key enzyme in the ketogenic pathway that supplies metabolic fuel to extrahepatic tissues. Enzyme deficiency may be due to a variety of human mutations and can be fatal. Diminished activity has been explained based on analyses of recombinant human mutant proteins or, more recently, in the context of structural models for the enzyme. We report the experimental determination of a crystal structure at 2.1 A resolution of the recombinant human mitochondrial HMG-CoA lyase containing a bound activator cation and the dicarboxylic acid 3-hydroxyglutarate. The enzyme adopts a (betaalpha)(8) barrel fold, and the N-terminal barrel end is occluded. The structure of a physiologically relevant dimer suggests that substrate access to the active site involves binding across the cavity located at the C-terminal end of the barrel. An alternative hypothesis that involves substrate insertion through a pore proposed to extend through the barrel is not compatible with the observed structure. The activator cation ligands included Asn(275), Asp(42),His(233), and His(235); the latter three residues had been implicated previously as contributing to metal binding or enzyme activity. Arg(41), previously shown to have a major effect on catalytic efficiency, is also located at the active site. In the observed structure, this residue interacts with a carboxyl group of 3-hydroxyglutarate, the hydrolysis product of the competitive inhibitor 3-hydroxyglutaryl-CoA required for crystallization of human enzyme. The structure provides a rationale for the decrease in enzyme activity due to clinical mutations, including H233R, R41Q, D42H, and D204N, that compromise active site function or enzyme stability.

Skipping of exon 2 and exons 2 plus 3 of HMG-CoA lyase (HL) gene produces the loss of beta sheets 1 and 2 in the recently proposed (beta-alpha)8 TIM barrel model of HL

HMG-CoA lyase (HL) deficiency is a rare autosomal recessive genetic disorder that affects ketogenesis and leucine catabolism. We report a new Spanish patient who bears the frequent nonsense mutation G109T (Mediterranean mutation). This mutation can produce aberrant splicing with three mRNA variants: one of the expected size, the second with deletion of exon 2, and the third with deletion of exons 2 and 3. Recently our group proposed a 3D model for human HL containing a (beta-alpha)(8) (TIM) barrel structure. We have studied the effect of the deletions of exon 2 and exons 2 plus 3 on the proposed HL model. Exon 2 skipping led to the loss of beta-sheet 1, and the skipping of exons 2 and 3 caused the disappearance of alpha helix 1 and beta-sheets 1 and 2.-

Identification of a common novel mutation in Saudi patients with argininosuccinic aciduria

We have identified a common novel mutation (Q354X) in the argininosuccinate lyase (ASL) gene in Saudi patients with argininosuccinic aciduria (ASAuria; McKusick 207900). The two index patients were siblings, had a neonatal onset of the disease and were diagnosed based on the clinical presentation and confirmed by analysis of their dried blood spots (DBS) by tandem mass spectrometry (MS/MS). The ASL gene was then analysed by direct sequencing. A further 28 patients with a confirmed diagnosis of ASAuria based on MS/MS of their DBS were tested by sequencing for the presence of the Q354X mutation. This mutation was found in 14 out of the 28 patients (50%) tested. Our work indicates that the Q354X allele is common, may account for 50% of the abnormal ASL genes in the Saudi population, and is likely to be associated with the neonatal form of the disease. We recommend that all patients diagnosed with ASAuria in Saudi Arabia or of Arab origin be tested for this mutation and for Q116X, which has been described previously. In addition, further analysis is needed to identify other underlying disease mutations for ASAuria in the Saudi population.

The E37X is a common HMGCL mutation in Portuguese patients with 3-hydroxy-3-methylglutaric CoA lyase deficiency

3-Hydroxy-3-methylglutaric aciduria (OMIM 246450) is an autosomal recessive inborn error of the final step of leucine catabolic and ketogenic pathways, caused by deficiency of the enzyme 3-hydroxy-3-methylglutaryl CoA lyase (HL, HMGCL, EC 4.1.3.4). Clinically, deficiency of the enzyme results in metabolic acidosis, hyperammonemia, and infantile hypoketotic hypoglycaemia usually presenting during the first year of life with vomiting, lethargy, hypotonia, and sometimes with respiratory distress and coma. HL deficiency is relatively common in Arabic populations but seems to be rare in Europe. Our recent experience suggests that HL deficiency is the most frequent organic aciduria in the Portuguese population. We herein report on the molecular study of the HMGCL gene in 11 cases originated from the Northern area of Portugal. We detected the E37X (c.109G > T) mutation, in 84.1% of the alleles, one allele carried the V168fs(-2) (504_505delCT) and other allele the novel D204N (c.610G > A) mutation. The mutation of the last allele remained unidentified. The relatively high frequency of the "common" HMGCL Portuguese mutation makes useful the development of a rapid and specific molecular confirmation of new cases with HL deficiency in our country.

Molecular basis of 3-hydroxy-3-methylglutaric aciduria

3-Hydroxy-3-methylglutaric aciduria is a human autosomal recessive metabolic disorder that usually appears within the first year of life. The causes of this aciduria are lethal mutations in the gene encoding for 3-hydroxy-3-methylglutaryl coenzyme A lyase (HL). HL is a mitochondrial matrix enzyme that catalyzes the last step of ketogenesis and leucine catabolism. This gene has been mapped to chromosome 1 at locus 1pter-p33 and its genomic organisation comprises 9 exons whose sizes vary between 64-678 bp. The human cDNA sequence was reported in 1993 with the first genetic study of two Acadian-French Canadian siblings. To date, 24 mutations in 36 patients have been described; most of them are single-base substitutions causing amino acid replacements and a variety of splicing defects. In the population studied two mutations appear predominant: g.122GA (8 patients and 15 alleles) frequent in Saudi Arabia, and g.109GT (6 patients and 12 alleles), prevalent in Spain. At least seven mutations are clustered in the second half of exon 2 affecting aminoacids E37, R41 and D42 and conforming a possible hot spot. The genotype-phenotype correlation is difficult to establish since the probands received different treatments, and the onset of an acute episode frequently depends on external factors such as fasting or acute illness.

Investigation of conserved acidic residues in 3-hydroxy-3-methylglutaryl-CoA lyase: implications for human disease and for functional roles in a family of related proteins

3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) lyase catalyzes the divalent cation-dependent cleavage of HMG-CoA to form acetyl-CoA and acetoacetate. In metal-dependent aldol and Claisen reactions, acidic residues often function either as cation ligands or as participants in general acid/base catalysis. Site-directed mutagenesis was used to produce conservative substitutions for the conserved acidic residues Glu-37, Asp-42, Glu-72, Asp-204, Glu-279, and Asp-280. HMG-CoA lyase deficiency results from a human mutation that substitutes lysine for glutamate 279. The E279K mutation has also been engineered; expression in Escherichia coli produces an unstable protein. Substitution of alanine for glutamate 279 produces a protein that is sufficiently stable for isolation and retains substantial catalytic activity. However, thermal inactivation experiments demonstrate that E279A is much less stable than wild-type enzyme. HMG-CoA lyase deficiency also results from mutations at aspartate 42. Substitutions that eliminate a carboxyl group at residue 42 perturb cation binding and substantially lower catalytic efficiency (104-105-fold decreases in specific activity for D42A, D42G, or D42H versus wild-type). Substitutions of alanine for the other conserved acidic residues indicate the importance of glutamate 72. E72A exhibits a 200-fold decrease in kcat and >103-fold decrease in kcat/Km. E72A is also characterized by inflation in the Km for activator cation (26-fold for Mg2+; >200-fold for Mn2+). Similar, but less pronounced, effects are measured for the D204A mutant. E72A and D204A mutant proteins both bind stoichiometric amounts of Mn2+, but D204A exhibits only a 2-fold inflation in KD for Mn2+, whereas E72A exhibits a 12-fold inflation in KD (23 microm) in comparison with wild-type enzyme (KD = 1.9 microm). Acidic residues corresponding to HMG-CoA lyase Asp-42 and Glu-72 are conserved in the HMG-CoA lyase protein family, which includes proteins that utilize acetyl-CoA in aldol condensations. These related reactions may require an activator cation that binds to the corresponding acidic residues in this protein family.

Structural (betaalpha)8 TIM barrel model of 3-hydroxy-3-methylglutaryl-coenzyme A lyase

This study describes three novel homozygous missense mutations (S75R, S201Y, and D204N) in the 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) lyase gene, which caused 3-hydroxy-3-methylglutaric aciduria in patients from Germany, England, and Argentina. Expression studies in Escherichia coli show that S75R and S201Y substitutions completely abolished the HMG-CoA lyase activity, whereas D204N reduced catalytic efficiency to 6.6% of the wild type. We also propose a three-dimensional model for human HMG-CoA lyase containing a (betaalpha)8 (TIM) barrel structure. The model is supported by the similarity with analogous TIM barrel structures of functionally related proteins, by the localization of catalytic amino acids at the active site, and by the coincidence between the shape of the substrate (HMG-CoA) and the predicted inner cavity. The three novel mutations explain the lack of HMG-CoA lyase activity on the basis of the proposed structure: in S75R and S201Y because the new amino acid residues occlude the substrate cavity, and in D204N because the mutation alters the electrochemical environment of the active site. We also report the localization of all missense mutations reported to date and show that these mutations are located in the beta-sheets around the substrate cavity.

Biochemical and molecular analyses in three patients with 3-hydroxy-3-methylglutaric aciduria

Two methods, spectrophotometry and HPLC, were compared in the analyses of 3-hydroxy-3-methylglutaryl-CoA lyase (HL) activity in three unrelated Czech patients with 3-hydroxy-3-methylglutaric (HMG) aciduria and their family members. The HL activities in cultured fibroblasts and/or isolated lymphocytes of probands were below the detection limits of the methods used. Both methods were also suitable for recognition of all heterozygotes in affected families. We searched for pathogenic mutations in the HL gene. Molecular analyses revealed that two patients are homozygous for known mutation H233R and R41Q, respectively, whereas the third patient is a compound heterozygote for the mutation H233R and a novel mutation Pro9fs(-1). This study expands the knowledge of the genotypic variability of the HMG aciduria.

3-Hydroxy-3-methylglutaric aciduria in an Italian patient is caused by a new nonsense mutation in the HMGCL gene

3-Hydroxy-3-methylglutaric aciduria is a rare autosomal recessive inborn error of metabolism caused by deficiency of the mitochondrial enzyme 3-hydroxy-3-methylglutaryl-CoA lyase (HMGCL). Up to now only a few mutations have been reported in the HMGCL gene. We report the first Italian patient, a female who presented metabolic acidosis at 3 days of age and then 3 months later. Analysis of urinary organic acids showed the excretion of 3-hydroxy-3-methylglutaric acid, 3-methylglutaconic acid, 3-methylglutaric acid, and 3-hydroxyisovaleric acid. A defect of HMGCL activity was suspected and then confirmed on cultured skin fibroblasts. Brain RM showed a diffuse mild abnormality of cerebral white matter in the periventricular regions, and the single voxel proton MRI spectroscopy showed abnormal peaks. In the patient's full-length HMGCL-cDNA a new c286C > T transition that leads to the stop codon Q96X was detected at the homozygous level. This mutation, that gives rise to a truncated protein, was confirmed in the patient's and also her parents' genomic DNA. The severe genetic lesion identified in the patient, which is in contrast with the mild clinical phenotype, stresses the importance of early diagnosis and therapy in HMGCL deficiency.

Mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase deficiency: clinical course and description of causal mutations in two patients

Hereditary deficiency of mitochondrial HMG-CoA synthase (mHS, OMIM 600234) is a poorly defined, treatable, probably underdiagnosed condition that can cause episodes of severe hypoketotic hypoglycemia. We present clinical follow-up and molecular analysis of the two known mHS-deficient patients. The diagnosis of mHS deficiency is challenging because the symptoms and metabolite pattern are not specific. Moreover, enzyme analysis is technically difficult and requires sampling of an expressing organ such as liver. The patients, now aged 16 and 6 y, have normal development and have had no further decompensations since diagnosis. Patient 1 is homozygous for a phenylalanine-to-leucine substitution at codon 174 (F174L). Interestingly, although the F174 residue is conserved in vertebrate mHS and cytoplasmic HS isozymes, a Leu residue is predicted in the corresponding position of HS-like sequences from Caenorhabditis elegans, Arabidopsis thaliana, and Brassica juncea. Bacterial expression of human F174L-mHS produces a low level of mHS polypeptide with no detectable activity. Similarly, in purified cytoplasmic HS, which in contrast to purified human mHS is stable and can be studied in detail, the corresponding F-->L substitution causes a 10,000-fold decrease in V(max) and a 5-fold reduction in thermal stability. Patient 2 is a genetic compound of a premature termination mutation, R424X, and an as-yet uncharacterized mutant allele that is distinguishable by intragenic single nucleotide polymorphisms that we describe. Molecular studies of mHS are useful in patients with a suggestive clinical presentation.

Hypoglycemia in association with various organic and amino acid disorders

A number of organic and amino acidemias, particularly those that involve the oxidation of fatty acids, cause hypoglycemia intermittently. This may be associated with distrubances of acid base equilibrium and accumulation of lactic acid and/or ketone bodies. When such diseases are not diagnosed rapidly, they might lead to neurological crippling and, at times, death. As a group, these disorders involve more than 1 organ and their phenotypic expression may include all or a single system. The symptoms may appear soon after birth or as late as 1 year of age. Their early recognition and rapid intervention provide rewarding clinical outcome. With the recent advances in diagnostic techniques, such as the introduction of tandem mass spectrometry (MS), screening for these diseases now can be performed because rapid identification on a large scale is possible. The phenotypes, mutations involved, pathognomonic laboratory findings, prognosis, and treatment procedures available have been reviewed for major diseases.

Hypoglycemia in infants and children

Hypoglycemia is more common in the pediatric patient than in adults. This article discusses the many diagnoses that can be associated with hypoglycemia in infancy and childhood. A guide to help practitioners evaluate such patients and suggested treatments for many of these disorders are provided. As genetic diagnosis continues to develop, it is anticipated that the list of specific disorders associated with hypoglycemia in infancy and childhood will increase.

Mitochondrial disease in superoxide dismutase 2 mutant mice

Oxidative stress has been implicated in many diseases. The chief source of reactive oxygen species within the cell is the mitochondrion. We have characterized a variety of the biochemical and metabolic effects of inactivation of the mouse gene for the mitochondrial superoxide dismutase (CD1-Sod2(tm1Cje)). The Sod2 mutant mice exhibit a tissue-specific inhibition of the respiratory chain enzymes NADH-dehydrogenase (complex I) and succinate dehydrogenase (complex II), inactivation of the tricarboxylic acid cycle enzyme aconitase, development of a urine organic aciduria in conjunction with a partial defect in 3-hydroxy-3-methylglutaryl-CoA lyase, and accumulation of oxidative DNA damage. These results indicate that the increase in mitochondrial reactive oxygen species can result in biochemical aberrations with features reminiscent of mitochondrial myopathy, Friedreich ataxia, and 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.

Linkage disequilibrium mapping of complex disease: fantasy or reality?

In the past year, data about the level and nature of linkage disequilibrium between alleles of tightly linked SNPs have started to become available. Furthermore, increasing evidence of allelic heterogeneity at the loci predisposing to complex disease has been observed, which has lead to initial attempts to develop methods of linkage disequilibrium detection allowing for this difficulty. It has also become more obvious that we will need to think carefully about the types of populations we need to analyze in an attempt to identify these elusive genes, and it is becoming clear that we need to carefully re-evaluate the prognosis of the current paradigm with regard to its robustness to the types of problems that are likely to exist.

Two missense point mutations in different alleles in the 3-hydroxy-3-methylglutaryl coenzyme A lyase gene produce 3-hydroxy-3-methylglutaric aciduria in a French patient

Two novel point mutations in the 3-hydroxy-3-methylglutaryl coenzyme A lyase gene were found in a French patient with double heterozygous 3-hydroxy-3-methylglutaric aciduria. Amplification by reverse transcriptase-polymerase chain reaction of the mRNA using five different pairs of oligonucleotides produced no differences in the fragments amplified with respect to the control. Single-strand conformation polymorphism analysis showed that only one amplified fragment was different in the patient vs. control. Sequencing of the amplified fragments showed two missense point mutations, A698G and T788C, each of them mixed with the wild-type sequence. These mutations produced the changes H233R and L263P, leading to changes in the enzyme activity, which was largely abolished. The father and one brother of the proband were heterozygous for the L263P mutation and the mother and one daughter were heterozygous for the H233R mutation, which confirms the double-heterozygous character of the patient. Another sibling was free of the mutations. An enzymatic restriction analysis has been proposed to screen the occurrence of these two mutations in future patients.