Clinical findings and biochemical and molecular analysis of four patients with holocarboxylase synthetase deficiency

1H-Nuclear Magnetic Resonance Analysis of Urine as Diagnostic Tool for Organic Acidemias and Aminoacidopathies

The utility of low-resolution 1H-NMR analysis for the identification of biomarkers provided evidence for rapid biochemical diagnoses of organic acidemia and aminoacidopathy. 1H-NMR, with a sensitivity expected for a field strength of 400 MHz at 64 scans was used to establish the metabolomic urine sample profiles of an infant population diagnosed with small molecule Inborn Errors of Metabolism (smIEM) compared to unaffected individuals. A qualitative differentiation of the 1H-NMR spectral profiles of urine samples obtained from individuals affected by different organic acidemias and aminoacidopathies was achieved in combination with GC-MS. The smIEM disorders investigated in this study included phenylalanine metabolism; isovaleric, propionic, 3-methylglutaconicm and glutaric type I acidemia; and deficiencies in medium chain acyl-coenzyme and holocarboxylase synthase. The observed metabolites were comparable and similar to those reported in the literature, as well as to those detected with higher-resolution NMR. In this study, diagnostic marker metabolites were identified for the smIEM disorders. In some cases, changes in metabolite profiles differentiated post-treatments and follow-ups while allowing for the establishment of different clinical states of a biochemical disorder. In addition, for the first time, a 1H-NMR-based biomarker profile was established for holocarboxylase synthase deficiency spectrum.

Holocarboxylase synthetase deficiency pre and post newborn screening

Holocarboxylase synthetase deficiency is an autosomal recessive disorder of biotin metabolism resulting in multiple carboxylase deficiency. The typical presentation described in the medical literature is of neonatal onset within hours to weeks of birth with emesis, hypotonia, lethargy, seizures, metabolic ketolactic acidosis, hyperammonemia, developmental delay, skin rash and alopecia. The condition is screened for by newborn screening (NBS) tandem mass spectroscopy by elevated hydroxypentanoylcarnitine on dried blood spots. Urine organic acid profile may demonstrate elevated lactic, 3-OH isovaleric, 3-OH propionic, 3-MCC, methylcitric acids, and tiglylglycine consistent with loss of function of the above carboxylases. Here we describe a cohort of patients, 2 diagnosed pre-NBS and 3 post-NBS with broad differences in initial presentation and phenotype. In addition, prior to the advent of NBS, there are isolated reports of late-onset holocarboxylase synthetase deficiency in the medical literature, which describe patients diagnosed between 1 and 8 years of life, however to our knowledge there are no reports of late-onset HCLS being missed by NBS. Also we report two cases, each with novel pathogenic variants HCLS, diagnosed at age 3 years and 21 months respectively. The first patient had a normal newborn screen whilst the second had an abnormal newborn screen but was misdiagnosed as 3-methylcrotonylcarboxylase (3-MCC) deficiency and subsequently lost to follow-up until they presented again with severe metabolic acidosis.

Antenatal and postnatal radiologic diagnosis of holocarboxylase synthetase deficiency: a systematic review

BACKGROUND

Holocarboxylase synthetase deficiency results in impaired activation of enzymes implicated in glucose, fatty acid and amino acid metabolism. Antenatal imaging and postnatal imaging are useful in making the diagnosis. Untreated holocarboxylase synthetase deficiency is fatal, while antenatal and postnatal biotin supplementation is associated with good clinical outcomes. Although biochemical assays are required for definitive diagnosis, certain radiologic features assist in the diagnosis of holocarboxylase synthetase deficiency.

OBJECTIVE

To review evidence regarding radiologic diagnostic features of holocarboxylase synthetase deficiency in the antenatal and postnatal period.

MATERIALS AND METHODS

A systematic review of all published cases of holocarboxylase synthetase deficiency identified by a search of Pubmed, Scopus and Web of Science.

RESULTS

A total of 75 patients with holocarboxylase synthetase deficiency were identified from the systematic review, which screened 687 manuscripts. Most patients with imaging (19/22, 86%) had abnormal findings, the most common being subependymal cysts, ventriculomegaly and intraventricular hemorrhage.

CONCLUSION

Although the radiologic features of subependymal cysts, ventriculomegaly, intraventricular hemorrhage and intrauterine growth restriction may be found in the setting of other pathologies, these findings should prompt consideration of holocarboxylase synthetase deficiency in at-risk children.

[Delayed onset holocarboxylase synthetase deficiency with normal pyruvate carboxylase activity]

We report a case of holocarboxylase synthetase deficiency with normal pyruvate carboxylase activity in the lymphocytes of an 8 year-old girl with clinical toxicity without the classic dermatological involvement. The identification of three nucleotide changes in the holocarboxylase synthetase (HLCS) gene, only one of them described as a pathogenic mutation could be related to a slight variant of the disease that would explain the unusual presentation beyond the age of infant. Treatment with biotin at 40 mg/day with protein controlled diet allows normal physical growth and psychomotor development for their age.

Clinical Presentation and Positive Outcome of Two Siblings with Holocarboxylase Synthetase Deficiency Caused by a Homozygous L216R Mutation

Purpose The L216R mutation, seen in individuals of Polynesian descent, is considered one of the most severe mutations associated with holocarboxylase synthetase (HLCS) deficiency and is regarded as being unresponsive to biotin. This report describes the presentation and outcome in two surviving siblings, homozygous for this highly lethal mutation. Methods and results Both cases had perinatal head imaging findings of brain hemorrhage and subependymal cysts. Both had metabolic decompensation within 24 h after birth consisting of metabolic acidosis, lactic acidosis, and thrombocytopenia. Biochemical profiles were consistent with HLCS deficiency, and genetic analysis confirmed homozygosity for the L216R mutation. After resolution of neonatal metabolic crisis, dosing of biotin was titrated on an outpatient basis to primarily control dermatitis. The eldest is currently on 1.2 g of oral biotin daily, well above any dose previously reported to treat HLCS deficiency. To date, neither patient has required hospital readmission for acute metabolic decompensation. At the age of 7, the eldest child is, to our knowledge, the oldest patient ever described in the literature who is homozygous for the L216R mutation. She has mild intellectual disability. Conclusion This report contrasts previous reports of poor outcomes and neonatal deaths in homozygous L216R patients. We also provide data on the potential upper tolerable limit of biotin. These cases suggest that the outcome of HCLS deficiency due to a homozygous L216R mutation, when diagnosed and treated early with high-level neonatal care and biotin, may not be as severe as previously reported.

Neonatal Seizures: When to Consider and How to Investigate for an Inborn Error of Metabolism

Seizures occur more frequently in the neonatal period than in the remainder of childhood. Neonatal seizures can have different aetiologies. Inborn errors of metabolism are rare causes of seizures in the newborn. However, they are an important cause of intractable neonatal seizures, accounting for 30% of cases. Diagnosis is necessary for timely institution of appropriate treatment and is important in determining clinical outcome. As these are genetic conditions, it allows for appropriate genetic counselling. We describe the clinical presentation of neonatal seizures and the investigation findings in symptomatic neonatal seizures and epilepsy syndromes that arise in the neonatal period. The approach in diagnosis and investigation of an underlying inborn error of metabolism is described and inborn errors of metabolism that are important causes of neonatal seizures are reviewed.

Diagnosis, treatment, follow-up and gene mutation analysis in four Chinese children with biotinidase deficiency

OBJECTIVE

To report the clinical course and explore the gene mutation spectrum of four Chinese children with biotinidase deficiency.

METHODS

Four Chinese patients aged 4 months to 8 years were referred to this study. Tandem mass spectrometry, gas chromatography-mass spectrometry and the determination of biotinidase activities were performed for selective screening of biotinidase deficiency. Four patients with biotinidase deficiency were diagnosed, treated with biotin and followed.

RESULTS

(1) Four patients with biotinidase deficiency were diagnosed by characteristic metabolites, such as elevated blood levels of 3-hydroxyisovalerylcarnitine (6.22 +/- 3.1 mumol/L), elevated 3-methylcrontonylglycine, methylcitrate and 3-hydroxypropionate in urine and very low biotinidase activities. (2) These patients have been treated with biotin for 1-8 years; two of them still have mental retardation, and two have irreversible hearing or vision disability. (3) In the four patients, six different mutations in the biotinidase gene were identified: c.98G:del7ins3, c.1369G>A (p. V457M), c.1384delA, c.1493_1494insT, c.1284C>A (p.Y428X) and c.1157G>A (p.W386X). The latter four mutations are novel variations. Seven out of eight mutations are located on exon 4 of the biotinidase gene.

CONCLUSIONS

Early recognition of biotinidase deficiency is crucial to avoid permanent damage. Determination of biotinidase activity should be included in neonatal screening in China. Exon 4 may be a hot-spot for biotinidase gene mutations in Chinese patients. Four novel gene variations may be disease-causing mutations and should be confirmed by expression studies.

Structural and functional studies of the biotin protein ligase from Aquifex aeolicus reveal a critical role for a conserved residue in target specificity

Biotin protein ligase (BPL; EC 6.3.4.15) catalyses the formation of biotinyl-5'-AMP from biotin and ATP, and the succeeding biotinylation of the biotin carboxyl carrier protein. We describe the crystal structures, at 2.4 A resolution, of the class I BPL from the hyperthermophilic bacteria Aquifex aeolicus (AaBPL) in its ligand-free form and in complex with biotin and ATP. The solvent-exposed beta- and gamma-phosphates of ATP are located in the inter-subunit cavity formed by the N- and C-terminal domains. The Arg40 residue from the conserved GXGRXG motif is shown to interact with the carboxyl group of biotin and to stabilise the alpha- and beta-phosphates of the nucleotide. The structure of the mutant AaBPL R40G in both the ligand-free and biotin-bound forms reveals that the mutated loop has collapsed, thus hindering ATP binding. Isothermal titration calorimetry indicated that the presence of biotin is not required for ATP binding to wild-type AaBPL in the absence of Mg(2+), and the binding of biotin and ATP has been determined to occur via a random but cooperative process. The affinity for biotin is relatively unaffected by the R40G mutation. In contrast, the thermodynamic data indicate that binding of ATP to AaBPL R40G is very weak in the absence or in the presence of biotin. The AaBPL R40G mutant remains catalytically active but shows poor substrate specificity; mass spectrometry and Western blot studies revealed that the mutant biotinylates both the target A. aeolicus BCCPDelta67 fragment and BSA, and is subject to self-biotinylation.

Biotin metabolism defect - A case report

Defects in biotin metabolism are mainly associated with either the enzyme Biotinidase or Holocarboxylase synthetase. Defects in either enzymes depletes biotin utilization by the cells. Holocarboxylase synthetase deficiency is an inherited disorder in which the body is unable to use the vitamin biotin effectively. This condition is inherited in an autosomal recessive pattern. We present a case of a 9 year old girl with atypical symptomology as a case holocarboxylase synthetase deficiency, who demonstrated an increased excretion of propionic and methyl malonic acids, with her biotinidase activity being normal. She demonstrated remarkable improvement on biotin supplementation.

Management of a patient with holocarboxylase synthetase deficiency

We investigated in a patient with holocarboxylase synthetase deficiency, the relation between the biochemical and genetic factors of the mutant protein with the pharmacokinetic factors of successful biotin treatment. A girl exhibited abnormal skin at birth, and developed in the first days of life neonatal respiratory distress syndrome and metabolic abnormalities diagnostic of multiple carboxylase deficiency. Enzyme assays showed low carboxylase activities. Fibroblast analysis showed poor incorporation of biotin into the carboxylases, and low transfer of biotin by the holocarboxylase synthetase enzyme. Kinetic studies identified an increased Km but a preserved Vmax. Mutation analysis showed the child to be a compound heterozygote for a new nonsense mutation Q379X and for a novel missense mutation Y663H. This mutation affects a conserved amino acid, which is located the most 3' of all recorded missense mutations thus far described, and extends the region of functional biotin interaction. Treatment with biotin 100mg/day gradually improved the biochemical abnormalities in blood and in cerebrospinal fluid (CSF), corrected the carboxylase enzyme activities, and provided clinical stability and a normal neurodevelopmental outcome. Plasma concentrations of biotin were increased to more than 500 nM, thus exceeding the increased Km of the mutant enzyme. At these pharmacological concentrations, the CSF biotin concentration was half the concentration in blood. Measuring these pharmacokinetic variables can aid in optimizing treatment, as individual tailoring of dosing to the needs of the mutation may be required.

Carnitine transporter and holocarboxylase synthetase deficiencies in The Faroe Islands

Carnitine transporter deficiency (CTD) and holocarboxylase synthetase deficiency (HLCSD) are frequent in The Faroe Islands compared to other areas, and treatment is available for both disorders. In order to evaluate the feasibility of neonatal screening in The Faroe Islands we studied detection in the neonatal period by tandem mass spectrometry, carrier frequencies, clinical manifestations, and effect of treatment of CTD and HLCSD. We found 11 patients with CTD from five families and 8 patients with HLCSD from five families. The natural history of both disorders varied extensively among patients, ranging from patients who presumably had died from their disease to asymptomatic individuals. All symptomatic patients responded favourably to supplementation with L: -carnitine (in case of CTD) or biotin (in case of HLCSD), but only if treated early. Estimates of carrier frequency of about 1:20 for both disorders indicate that some enzyme-deficient individuals remain undiagnosed. Prospective and retrospective tandem mass spectrometry (MS/MS) analyses of carnitines from neonatally obtained filter-paper dried blood-spot samples (DBSS) uncovered 8 of 10 individuals with CTD when using both C(0) and C(2) as markers (current algorithm) and 10 of 10 when using only C(0) as marker. MS/MS analysis uncovered 5 of 6 patient with HLCSD. This is the first study to report successful neonatal MS/MS analysis for the diagnosis of HLCSD. We conclude that CTD and HLCSD are relatively frequent in The Faroe Islands and are associated with variable clinical manifestations, and that diagnosis by neonatal screening followed by early therapy will secure a good outcome.

First prenatal molecular diagnosis in a family with holocarboxylase synthetase deficiency

OBJECTIVES

We report on the first prenatal molecular diagnosis of holocarboxylase synthetase (HLCS) deficiency in the fourth pregnancy of an at-risk family. This disorder is a rare autosomal recessive inborn error of metabolism, leading to a multiple carboxylase defect (MCD). HLCSD diagnosis was performed postmortem in the proband on DNA from autoptic biological material. Molecular analysis of the proband's entire HLCS gene by direct sequencing identified the R508W amino acid change, at the homozygous status.

METHODS

Fetal DNA was isolated from chorionic villus sampling at 11 weeks of gestation. Direct sequencing of exon 6 of the fetal HLCS gene was performed.

RESULTS

The R508W mutation was identified in the fetal DNA at the homozygous level. The genetic lesion was confirmed on abortive tissue.

CONCLUSION

Molecular diagnosis has several advantages over enzymatic activity assay of carboxylases in chorionic villi or amniocytes. It can be performed earlier, is faster, and the response time is shorter.

Mutations in the holocarboxylase synthetase gene HLCS

Holocarboxylase synthetase (HLCS) deficiency is an autosomal recessive disorder. HLCS is an enzyme that catalyzes biotin incorporation into carboxylases and histones. Since the first report of the cDNA sequence, 30 mutations in the HLCS gene have been reported. Mutations occur throughout the entire coding region except exons 6 and 10. The types of mutations are one single amino acid deletion, five single nucleotide insertions/deletions, 22 missense mutations, and two nonsense mutations. The only intronic mutation identified thus far is c.1519+5G>A (also designated IVS10+5G>A), which causes a splice error. Several lines of evidence suggest that c.1519+5G>A is a founder mutation in Scandinavian patients. Prevalence of this mutation is about 10 times higher in the Faroe Islands than in the rest of the world. The mutations p.L237P and c.780delG are predominant only in Japanese patients. These are probably founder mutations in this population. Mutations p.R508W and p.V550M are identified in several ethic groups and accompanied with various haplotypes, suggesting that these are recurrent mutations. There is a good relationship between clinical biotin responsiveness and the residual activity of HLCS. A combination of a null mutation and a point mutation that shows less than a few percent of the normal activity results in neonatal onset. Patients who have mutant HLCS with higher residual activity develop symptom after the neonatal period and show a good clinical response to biotin therapy.

Holocarboxylase synthetase deficiency presenting as ichthyosis

Holocarboxylase synthetase deficiency is a rare autosomal recessive disorder of biotin metabolism. Clinical manifestations usually present within the first few days of life and include severe acidosis, feeding difficulties, breathing abnormalities, vomiting, seizures, progressive loss of consciousness, coma, and death. Skin findings, when present, usually develop within the first weeks of life and are described as an erythroderma-like dermatitis involving the eyebrows, eyelashes, and scalp. We were asked to consult on a newborn with a collodion membrane and severe metabolic acidosis who was eventually diagnosed with holocarboxylase synthetase deficiency and ichthyosis. The diagnosis of holocarboxylase synthetase deficiency might be considered in a newborn with collodion membrane, ichthyosis, and acidosis.

Severe holocarboxylase synthetase deficiency with incomplete biotin responsiveness resulting in antenatal insult in samoan neonates

We describe 7 Polynesian babies with a unique severe form of holocarboxylase synthetase deficiency characterized by antenatal growth retardation, subependymal cysts, only partial response to biotin, and a poor outcome.