[Late onset 3-HMG-CoA lyase deficiency: a rare but treatable disorder]. / Déficit en 3-HMG-CoA lyase à révélation tardive : savoir reconnaître une maladie rare mais traitable.

3-Hydroxy-3-methylglutaric aciduria is a rare autosomal recessive genetic disorder due to a deficiency of the 3-hydroxy-3-methylglutarylCoA lyase (HMG-CoA lyase), a mitochondrial enzyme involved in ketogenesis and in the final step of l-leucine catabolism. HMG-CoA lyase deficiency can lead, in particular circumstances, such as fever, prolonged fasting or digestive disorders, to brutal and severe hypoglycemia with metabolic acidosis and sometimes fatal coma. We report on a new case of 3-hydroxy-3-methylglutaric aciduria particular by its late onset in a 3-year-old patient. Molecular investigation identified two new sequence modifications in the HMGCL gene: c.494G>A (p.Arg165Gln) and c.820G>A (p.Gly274Arg). We remind about this case report that the therapeutical is mainly preventive and allows a very good prognosis for this disease. Long-term treatment consists in limited fasting time, continuous low protein diet and l-carnitine supplementation. Preventive measures are essential: prevention of fasting and emergency treatment during intercurrent infections.

NTBC treatment in tyrosinaemia type I: long-term outcome in French patients.

We describe a retrospective study of long-term outcome of 46 patients treated and regularly followed in France with 2-(2-nitro-4-trifluoromethylbenzoyl)-1, 3-cyclohexanedione (NTBC) for tyrosinaemia type I. Most had initial good response with normalization of liver function and metabolic parameters. Only one infant had no response to treatment and required liver transplantation. Among the 45 long-term treated patients, three underwent secondary liver transplantation: one for cirrhosis and two because of hepatocellular carcinoma. One of the latter died of transplantation complications, so that the overall survival rate was 97.5%. However, 17 of 45 showed persistent abnormal liver imaging (heterogeneous liver) and 6 had cirrhosis. Furthermore, 15 had persistently elevated levels of alpha-fetoprotein, highlighting the question of the persistent risk of carcinoma. Quality of life was usually good but compliance problems were frequent, mainly regarding the low phenylalanine-tyrosine diet. Few adverse effects were observed. A main concern was the high frequency of cognitive impairment causing schooling problems, which may be related to persistent chronic hypertyrosinaemia. In conclusion, this series confirms that NTBC treatment has clearly improved the vital prognosis and quality of life of tyrosinaemia type I patients but that many late complications persist. Long-term studies are necessary to determine whether this drug may prevent or only delay liver complications, andto survey the possible risks of the drug. A more restricted diet could be necessary to prevent the neurological impact of the disease.

[Late diagnosis of a McArdle disease's case (type V glycogenosis)]. / Diagnostic tardif d'une maladie de McArdle (glycogénose de type V).

McArdle's disease is a metabolic myopathy characterized by a myophosphorylase deficiency resulting in an inability to degrade glycogen stores. We report the case of a 48 years old patient who complained since adolescence of rest and exercise myalgias and presented a chronic increased plasma creatine kinase activity. First, a maximal exercise test was performed. This test demonstrated a quasi lack of rise of respiratory exchange ratio and of blood lactate, possibly due to a glycogenolytic/glycolytic pathway deficiency. Second, a biopsy of vastus lateralis muscle was performed using Bergström needle. As expected, the analysis of mitochondrial function was normal. The in vitro screening test of the glycogenolysis/glycolysis pathway showed a lack of lactate production in presence of glycogen substrate. The study of muscular metabolism of glycogen revealed a glycogen accumulation and a decrease of active and total phosphorylase activities. These data allowed us to diagnose a type V glycogenosis, or McArdle's disease. The patient appeared heterozygous for the most frequent mutation (p.R50X).

Diagnostic value of serum immunoglobulinaemia D level in patients with a clinical suspicion of hyper IgD syndrome.

OBJECTIVE: The hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS) was originally defined by the presence of a high serum level of immunoglobulin D associated with recurrent fever. Since the discovery of the mevalonate kinase gene (MVK) gene encoding the mevalonate kinase enzyme, most patients with a clinical diagnostic of HIDS are now found to have a mevalonate kinase deficiency based on metabolic and genetic data. We aimed to asses the value of a high IgD serum level for the diagnosis of HIDS in a cohort of patients with a phenotype of recurrent fever, and to characterize patients with a high IgD serum level without mevalonate kinase mutation. METHODS: Main clinical and biological data of 50 patients who presented with clinical signs compatible with HIDS have been prospectively registered on a standard form. Clinical data have been analysed according the IgD serum level and the presence of MVK mutation. RESULTS: The metabolic and genetic data establishing the diagnosis of HIDS correlated in all cases. In this series of 50 patients, the sensitivity of a high IgD value for the diagnosis of HIDS is 0.79. In five patients with MVK mutation, IgD levels were found to be in the normal range. Likelihood ratios indicate that IgD measurement is not relevant for the diagnostic of HIDS. Most patients with a high serum IgD level and no MVK mutation have no definite diagnosis. CONCLUSION: The clinical relevance of the IgD measurement for the diagnosis of MKD in our population appears as poor, as reflected by likelihood ratios which are both close to 1.

Genetic heterogeneity of the GLDC gene in 28 unrelated patients with glycine encephalopathy.

Glycine encephalopathy, or nonketotic hyperglycinaemia (NKH; Mckusick 238300) is a severe autosomal recessive disease due to a defect in the glycine cleavage system (GCS), which is a complex of four subunits: P-, T-, H- and L-proteins. A P-protein (glycine decarboxylase or GLDC) deficiency was reported in about 80% of NKH patients. We performed mutation analysis of the complete coding sequence of the GLDC gene in 28 unrelated patients with neonatal NKH using denaturing high-performance liquid chromatography (DHPLC) and sequencing. Forty different gene alterations were identified, confirming the large molecular heterogeneity of the GLDC gene. Eighteen alterations were clearly disease-causing: two large deletions, four one-base deletions (c.28delC, c.1175delC, c.2186delC, c.2422delA), one 1-base insertion (c.1002_1003insT), one 4-base insertion (c.1285_1286insCAAA), one insertion/deletion (c.2153_2155delinsTCCTGGTTTA), five nonsense mutations (p.E153X, p.R236X, p.E270X, p.R337X, p.R424X) and four splice site mutations (c.861+1G > T, c.1402-1C > G, c.2316-1G > A, c.2919+1G > A). Additionally, we identified one intronic mutation outside the consensus splice sites (c.2838+5G > A) and 21 nucleotide substitutions leading to amino acid change (including three previously described mutations: p.T269M, p.R461Q, p.G771R), the pathogenicity of which should be confirmed by expression studies (p.S132W, p.Y138F, p.G171A, p.T187K, p.R212K, p.T269M, p.R373W, p.I440N, p.R461Q, p.N533Y, p.C644F, p.H651R, p.V705M, p.N732K, p.G771R, p.H775R, p.T830M, p.A841P, p.D880V, p.S957P and p.R966G). Mutation analysis allowed us to identify sequence alterations in both alleles for 19 patients and in one allele for 7 patients One patient was carrying three mutations (p.Y138F, p.T269M and p.E153X) and one patient was carrying two amino acid substitutions on the same allele (p.V705M and p.R212K) and an unidentified mutation on the other allele. No mutation could be found in two patients, suggesting possible defects in the H-protein or gene alterations that could not be identified by our technique. The potential use of genotype determination for prenatal diagnosis is emphasized.

[Severe hyperhomocysteinemia revealing homocystinuria in two young adults with mild phenotype]. / Hyperhomocystéinémie sévère révélant une homocystinurie chez deux jeunes adultes présentant un phénotype peu marqué

INTRODUCTION: To the request of total plasma homocysteine determination in the investigation of vascular disease, diagnosis of homocystinuria in young adult patients with mild phenotype is not so rare. EXEGESIS: A 26-year-old man developed embolic cerebral infarction and a 22-year-old woman presented a right renal venous thrombosis one week after delivery. In each case, high concentration of total plasma homocysteine was first found and plasma and urinary amino acids analysis later on directed the diagnosis towards homocystinuria. Finally, reduced skin fibroblast cystathionine beta-synthase activity confirmed the diagnosis of homocystinuria. CONCLUSION: Total plasma homocysteine determination must be determined for screening for hyperhomocysteinemia in young adults with venous thromboembolism without characteristic phenotypic features of homocystinuria.

Fetal type IV glycogen storage disease: clinical, enzymatic, and genetic data of a pure muscular form with variable and early antenatal manifestations in the same family.

We report on a family of three consecutive fetuses affected by type IV glycogen storage disease (GSD IV). In all cases, cervical cystic hygroma was observed on the 12-week-ultrasound examination. During the second trimester, fetal hydrops developed in the first pregnancy whereas fetal akinesia appeared in the second pregnancy. The diagnosis was suggested by microscopic examination of fetal tissues showing characteristic inclusions exclusively in striated fibers, then confirmed by enzymatic studies on frozen muscle. Antenatal diagnosis was performed on the third and fourth pregnancies: cervical cystic hygroma and low glycogen branching enzyme (GBE) activity on chorionic villi sample (CVS) were detected in the third pregnancy whereas ultrasound findings were normal and GBE activity within normal range on CVS in the fourth pregnancy. Molecular analysis showed that the mother was heterozygous for a c.1471G > C mutation in exon 12, leading to the replacement of an alanine by a tyrosine at codon 491 (p.A491T); the father was heterozygous for a c.895G > T mutation in exon 7, leading to the creation of a stop codon at position 299 (p.G299X). GSD IV has to be considered in a context of cervical cystic hygroma with normal karyotype, particularly when second trimester hydrops or akinesia develop. Enzymatic analysis of GBE must be performed on CVS or amniotic cells to confirm the diagnosis. Characteristic intracellular inclusions are specific to the disease and should be recognized, even in macerated tissues after fetal death. Genetic analysis of the GBE gene may help to shed some light on the puzzling diversity of GSD IV phenotypes.

Atypical MRI findings in Canavan disease: a patient with a mild course.

Canavan disease is a severe, progressive leukodystrophy with an autosomal recessive inheritance, caused by aspartoacylase (ASPA) deficiency. The characteristic MRI features include diffuse, symmetrical white matter degeneration in the subcortical areas, with bilateral involvement of the globus pallidus. Proton magnetic resonance spectroscopy of the brain shows an increase in the concentration of N-acetylaspartic acid (NAA). The altered NAA metabolism has been traced to mutations in the gene encoding ASPA, located on chromosome 17 (17p13-ter). We present here a patient with a mild form of Canavan disease confirmed with the absent ASPA activity, atypical MRI findings, related to compound heterozygosity for a missense mutation, p.Tyr288Cys, and the known pan-European mutation, the p.Ala305Glu.

Possible genotype-phenotype correlations in children with mild clinical course of Canavan disease.

Canavan disease is characterised as a rare, neurodegenerative disease that usually causes death in early childhood. It is an autosomal recessive disorder due to an aspartoacylase (ASPA) deficiency. The causative gene has been mapped to chromosome 17 pter-p13. Here we describe three affected children from two Greek families with an unusually mild course of Canavan disease. All children presented with muscular hypotonia and macrocephaly. Diagnosis was based on elevated N-acetylaspartate in urine, reduced aspartoacylase activity in fibroblasts, and marked white matter changes on cerebral imaging. All three affected individuals exhibited continuous psychomotor development without any regression. Genetic analyses revealed compound heterozygous mutations (Y288 C; F295 S) in two individuals. The Y288 C variant was previously described in a child with macrocephaly, mild developmental delay, increased signal intensity in the basal ganglia, partial cortical blindness and retinitis pigmentosa, and slightly elevated N-acetylaspartate in the urine. Demonstration of the same variant in two unusually mildly affected Canavan disease patients and absence of this variant in 154 control chromosomes suggest a possible pathogenic role in mild Canavan disease. In the third individual, two homozygous sequence variants were identified, which comprise the known G274R mutation and a novel K213E variant.

False-positive results in neonatal screening for cystic fibrosis based on a three-stage protocol (IRT/DNA/IRT): Should we adjust IRT cut-off to ethnic origin?

Since 1979, newborn screening for cystic fibrosis (CF) has been possible by measuring immunoreactive tryspinogen (IRT) in blood spots. In France, a programme based on a three-stage strategy (IRT/DNA/IRT) started in 2002. In the Rhône-Alpes area, the positive screening rate (i.e. the proportion of samples sent for genotyping) observed after the first IRT measurement was higher than the expected rate (0.65% versus 0.50%), without a greater CF incidence. We hypothesized that the IRT reference range could differ according to the ethnic origin of the newborns. 35 141 newborns were studied and divided into two groups: European ethnic group 26 324 (75%) and North African ethnic group 8817 (25%). 243 positive newborns were identified: 146 (60%) in the European ethnic group and 97 (40%) in the North African ethnic group. Three CF patients and 11 unaffected heterozygotes were found in the European group, but no mutations were found in the North African group. Mean IRT values and the percentage of IRT values over the cut-off were significantly higher in the North African group than in the European group (mean IRT = 21.17 microg/L and 19.74 microg/L, p < 0.0001; %IRT > cut-off = 1.1% and 0.5%, respectively). For the positive screened newborns, term and IRT mean were comparable, whereas birth weight was higher in the North African ethnic group. These results lead us to conclude that (i) newborns from families of North African origin have higher IRT values and (ii) most of the positive screened newborns in this population could be considered as 'false positives'. These conclusions could explain, in part, the large variations seen in the positive screening rate in the French CF neonatal screening and raise the question whether it is relevant to adapt cut-off to ethnic origin of the newborns.

First-trimester enzymatic and molecular prenatal diagnosis of mevalonic aciduria.

Prenatal diagnosis was offered to a family at risk of mevalonic aciduria. A chorionic villus sample was obtained and both mevalonate kinase activity and mutation analysis were done. An affected fetus was diagnosed.

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.

[Delayed diagnosis of homocystinuria by major deficiency in cystathionine beta synthase]. / Diagnostic tardif d'homocystinurie par déficit majeur en cystathionine beta synthase.

INTRODUCTION: Homocystinuria due to cystathionine beta synthase (CBS) deficiency is a special type of hyperhomocysteinemia because of its clinical expression (thrombotic events, ectopic lens and mental retardation). It's a rare, hereditary recessive autosomic disease generally diagnosed during childhood. EXEGESIS: Thrombophilia examination in a 50-year-old man found a dramatically increase homocysteinemia. Homocystinuria, profile of plasmatic amino acids and reduced CBS activity, (0.05 microkat/kg protein; N = 1.5 +/- 0.8) confirmed homocystinuria's diagnosis. Family study demonstrates that three siblings suffer from homocystinuria. Vitamin enriched diet with pyridoxin, vitamin B12 and folates induced reducing hyperhomocysteinemia and homocystinuria. CONCLUSION: This case report, original because of the diagnosis age, suggests a hyperhomocysteinemia's screening in patients with recurrent thrombotic events.

Seventeen novel mutations that cause profound biotinidase deficiency.

We report 17 novel mutations that cause profound biotinidase deficiency. Six of the mutations are due to deletions, whereas the remaining 11 mutations are missense mutations located throughout the gene and encode amino acids that are conserved in mammals. Our results increase the total number of different mutations that cause biotinidase deficiency to 79. These additional mutations will undoubtedly be helpful in identifying structure/function relationships once the three-dimensional structure of biotinidase is determined.

An intestinal obstruction in an eight-month-old child suffering from mevalonic aciduria.

UNLABELLED: This report describes a case of mevalonate kinase deficiency diagnosed at 1 mo of age. Soon after delivery, symptoms were suggestive of congenital infection. An intestinal occlusion occurred towards the age of 8 mo. CONCLUSION: Mevalonate kinase deficiency has variable clinical and biological signs which can lead to a delay in diagnosis. This is the first reported occurrence of bowel obstruction in this disease and the resemblance to a congenital infection in the neonatal period must be emphasized.

Identification of 5 novel mutations in the AGXT gene.

In order to identify additional genotypes in primary hyperoxaluria type 1, we sequenced the AGXT genes of 9 patients. We report 5 new mutations. Three are splice-site mutations situated at the end of intron 4 and 8 (647-1G>A, 969-1G>C, 969-3C>G), one is a missense mutation in exon 5 (D183N), and one is a short duplication in exon 2 (349ins7). Their consequence is always a lack of enzymatic activity of the Alanine-Glyoxylate Aminotransferase (AGT); for 4 of them, we were able to deduce that they were associated to the absence of AGT protein. These mutations are rare, as they have been found on one allele in our study (except 969-3C>G present in 2 unrelated families), and have not been previously reported.

Non-concordance of CVS and liver glycine cleavage enzyme in three families with non-ketotic hyperglycinaemia (NKH) leading to false negative prenatal diagnoses.

We report three false negative prenatal diagnostic results, using direct measurement of glycine cleavage enzyme activity in uncultured chorionic villus tissue from 290 pregnancies at risk for non-ketotic hyperglycinaemia (NKH). Testing was done by two centres: Vancouver, Canada and Lyon, France. One false negative result had activity near the lower limit of the normal range but two samples gave completely normal results well within the control range. All three pregnancies continued and the three children were born affected with NKH. Because of the first result, we now counsel that there is a grey zone of uninterpretable activity where affected and normal enzyme values overlap. Because of the other two results we now counsel that there is an approximately 1% chance of a pregnancy with a normal CVS activity resulting in an affected child. The clinical and biochemical findings in the three families are discussed.

Partial deletion of the AGXT gene (EX1_EX7del): A new genotype in hyperoxaluria type 1.

Primary hyperoxaluria type 1 (PH1) is a rare autosomal (2q37.3) recessive metabolic disease caused by a deficiency of the hepatic peroxisomal enzyme alanine:glyoxylate amino transferase. Molecular heterogeneity is important in PH1 as most of the patients (if the parents are unrelated) are compound heterozygotes for rare mutations. We describe the first large deletion in the AGXT gene, removing exons 1 to 7 (EX1_EX7del) that was responsible for one case of severe PH1. This 10 kb deletion was identified by Southern blotting of genomic DNA digested by Xba I and hybridized with different exonic probes. Both parents (from Turkey) are first cousin and carry the deletion. It is of note that the presently reported patient did not exhibit any AGT catalytic activity and even so, he progressed towards end-stage renal disease only at 19 years old.

Effect of sodium benzoate in the treatment of atypical nonketotic hyperglycinaemia.

A 6-month-old girl presented with hypotonia and mild psychomotor retardation. Subsequently, an atypical manifestation of a nonketotic hyperglycinaemia was diagnosed, confirmed by significantly reduced activity of the glycine cleavage system in the liver tissue. After the patient developed hypsarrhythmia and had a single cerebral seizure, treatment with both sodium benzoate and dextromethorphan was started. During the following year, the girl was free of seizures with improvement of the EEG activity and showed retarded but continuously progressing psychomotor development. At the age of 20 months she began to walk freely but had generalized muscular hypotonia and moderate mental retardation. Discontinuation of dextromethorphan medication after one year of treatment did not change the clinical and electroencephalographic status. However, after cessation of sodium benzoate therapy, epileptic activity in the EEG and behavioural changes occurred. These changes disappeared promptly after sodium benzoate therapy was reinstituted. Thus, this case of mild atypical nonketotic hyperglycinaemia with only moderate psychomotor retardation and without epilepsy benefited from treatment with sodium benzoate in terms of electroencephalographic and behavioural changes.