Clinical, biochemical, and genetic analysis of a Chinese Han pedigree with holocarboxylase synthetase deficiency: a case report.

BACKGROUND: Holocarboxylase synthetase (HLCS) deficiency is a rare inborn disorder of biotin metabolism, which results in defects in several biotin-dependent carboxylases and presents with metabolic ketoacidosis and skin lesions. CASE PRESENTATION: In this paper, we report a Chinese Han pedigree with HLCS deficiency diagnosed by using next-generation sequencing and validated with Sanger sequencing of the HLCS and BTD genes. The Chinese proband carries the common missense mutation c.1522C > T (p.Arg508Trp) in exon 9 of the HLCS gene, which generates an increased Km value for biotin. A novel frameshift mutation c.1006_1007delGA (p.Glu336Thrfs*15) in exon 6 of the HLCS gene is predicted to be deleterious through PROVEAN and MutationTaster. A novel heterozygous mutation, c.638_642delAACAC (p.His213Profs*4), in the BTD gene is also identified. CONCLUSIONS: The Chinese proband carries the reported Arg508Trp variant, the novel 2-bp frameshift mutation c.1006_1007delGA (p.Glu336Thrfs*15), which expands the mutational spectrum of the HLCS gene, and the novel heterozygous mutation c.638_642delAACAC (p.His213Profs*4), which expands the mutational spectrum of the BTD gene. Furthermore, reversible hearing damage is rarely reported in patients with HLCS deficiency, which deserves further discussion.

[Delayed onset holocarboxylase synthetase deficiency with normal pyruvate carboxylase activity]. / Deficiencia de holocarboxilasa sintetasa de presentación tardía con actividad piruvato carboxilasa normal.

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.

Positive newborn screen in the biochemically normal infant of a mother with treated holocarboxylase synthetase deficiency.

Expanded programmes of newborn screening permit early diagnosis in time to prevent serious complications. These programmes have begun to detect patients who might otherwise remain asymptomatic. An additional confounding variable is the positive screen that results from maternal rather than neonatal disease. This was the case in an infant in whom elevated hydroxyisovalerylcarnitine (C(5)OH) in his newborn screen was the result of placental transfer from his mother, whose holocarboxylase synthetase deficiency was being successfully treated with biotin. The mother had been diagnosed and treated with biotin prenatally. She had no phenotypic feature of holocarboxylase synthetase deficiency, most importantly no episodes ever of acute metabolic acidosis. In the infant a repeat screen was also positive. On day 28 the infant's plasma C(5)OH carnitine was 0.05 mumol/L (normal) and urinary organic acids on day 39 were normal. The mother's excretion of 3-hydroxyisovaleric acid was 109 mmol/mol creatinine. These observations indicate that holocarboxylase synthetase deficiency is one more maternal metabolic disease which may lead to a positive screen in her unaffected newborn infant. They also make the point that holocarboxylase synthetase deficiency in an infant should be detectable in programmes of neonatal screening, which was not clear previously.

Impaired biotinidase activity disrupts holocarboxylase synthetase expression in late onset multiple carboxylase deficiency.

Biotinidase catalyzes the hydrolysis of the vitamin biotin from proteolytically degraded biotin-dependent carboxylases. This key reaction makes the biotin available for reutilization in the biotinylation of newly synthesized apocarboxylases. This latter reaction is catalyzed by holocarboxylase synthetase (HCS) via synthesis of 5'-biotinyl-AMP (B-AMP) from biotin and ATP, followed by transfer of the biotin to a specific lysine residue of the apocarboxylase substrate. In addition to carboxylase activation, B-AMP is also a key regulatory molecule in the transcription of genes encoding apocarboxylases and HCS itself. In humans, genetic deficiency of HCS or biotinidase results in the life-threatening disorder biotin-responsive multiple carboxylase deficiency, characterized by a reduction in the activities of all biotin-dependent carboxylases. Although the clinical manifestations of both disorders are similar, they differ in some unique neurological characteristics whose origin is not fully understood. In this study, we show that biotinidase deficiency not only reduces net carboxylase biotinylation, but it also impairs the expression of carboxylases and HCS by interfering with the B-AMP-dependent mechanism of transcription control. We propose that biotinidase-deficient patients may develop a secondary HCS deficiency disrupting the altruistic tissue-specific biotin allocation mechanism that protects brain metabolism during biotin starvation.

Microbial biotin protein ligases aid in understanding holocarboxylase synthetase deficiency.

The attachment of biotin onto the biotin-dependent enzymes is catalysed by biotin protein ligase (BPL), also known as holocarboxylase synthase HCS in mammals. Mammals contain five biotin-enzymes that participate in a number of important metabolic pathways such as fatty acid biogenesis, gluconeogenesis and amino acid catabolism. All mammalian biotin-enzymes are post-translationally biotinylated, and therefore activated, through the action of a single HCS. Substrate recognition by BPLs occurs through conserved structural cues that govern the specificity of biotinylation. Defects in biotin metabolism, including HCS, give rise to multiple carboxylase deficiency (MCD). Here we review the literature on this important enzyme. In particular, we focus on the new information that has been learned about BPL's from a number of recently published protein structures. Through molecular modelling studies insights into the structural basis of HCS deficiency in MCD are discussed.

[Gene mutation analysis in four Chinese patients with multiple carboxylase deficiency].

OBJECTIVE: Multiple carboxylase deficiency (MCD) is an autosomal recessive disorder. MCD is characterized by skin rash, metabolic acidosis, vomiting and psychomotor retardation. Depending on deficiency of the enzyme, MCD includes two different forms, biotinidase deficiency (BTD, OMIM 253260) and holocarboxylase synthetase deficiency (HLCSD, OMIM 253270). In this study, we analyzed gene mutations of four Chinese MCD patients and to explore the mutation spectrum and possibility of a molecular diagnosis. METHODS: All exons and their flanking introns of biotinidase gene and HLCS gene were screened by polymerase chain reaction combined with DNA direct sequencing in four Chinese MCD patients. Genomic DNA was extracted using a kit from the peripheral blood leukocytes of each patient. PCR amplification products were checked by 2% agarose gel electrophoresis and were subsequently sequenced with both the forward and reverse primers. RESULTS: All patients showed mutations in HLCS gene, whereas no mutation was found in biotinidase gene, proving that all the four patients had HLCS deficiency. Four previously reported mutations in HLCS gene were detected (Y456C, R508W, D634N and 780delG). A missense mutation of 1522C > T in exon 11 of HLCS gene, which was a homozygotic mutation, was identified in patient 1; a mutation of 1522C > T in exon 11 combined with a mutation of 1367A > G in exon 9, which was a compound heterozygotic mutation, was identified in patient 2; a mutation of 1522C > T in exon 11 combined with a mutation of 1900G > A in exon 13, which was a compound heterozygotic mutation, was identified in patient 3; a mutation of 1522C > T in exon 11 combined with a mutation of 780delG in exon 7, which was a compound heterozygotic mutation, was identified in patient 4. All the parents were carriers of mutations. No additional carrier of this four mutations was identified from 50 samples of Chinese controls. CONCLUSION: The 1522C > T (R508W) mutation probably represents a mutational hot-spot in Chinese HLCS deficiency patients while the 780delG mutation which was reported only in Japanese patients was found firstly in Chinese patients.