title: Isolated 3-methylcrotonyl-CoA carboxylase deficiency: evidence for an allele-specific dominant negative effect and responsiveness to biotin therapy.
abstract: Deficiency of 3-methylcrotonyl-CoA carboxylase (MCC) results in elevated excretion of 3-methylcrotonylglycine (3-MCG) and 3-hydroxyisovaleric acid (3-HIVA). MCC is a heteromeric mitochondrial enzyme comprising biotin-containing alpha subunits and smaller beta subunits, encoded by MCCA and MCCB, respectively. Mutations in these genes cause isolated MCC deficiency, an autosomal recessive disorder with a variable phenotype that ranges from severe neonatal to asymptomatic adult forms. No reported patients have responded to biotin therapy. Here, we describe two patients with a biochemical and, in one case, clinical phenotype of MCC deficiency, both of whom were responsive to biotin. The first patient presented at 3 months with seizures and progressive psychomotor retardation. Metabolic investigation at 2 years revealed elevated excretion of 3-MCG and 3-HIVA, suggesting MCC deficiency. High-dose biotin therapy was associated with a dramatic reduction in seizures, normalization of the electroencephalogram, and correction of the organic aciduria, within 4 weeks. MCC activity in fibroblasts was 25% of normal levels. The second patient, a newborn detected by tandem-mass-spectrometry newborn screening, displayed the same biochemical phenotype and remained asymptomatic with biotin up to the age of 18 months. In both patients, sequence analysis of the complete open reading frames of MCCA and MCCB revealed heterozygosity for MCCA-R385S and for the known polymorphic variant MCCA-P464H but revealed no other coding alterations. MCCA-R385S is unusual, in that it has a normal amount of MCC alpha protein but confers no MCC activity. We show that MCCA-R385S, but not other MCCA missense alleles, reduces the MCC activity of cotransfected MCCA-wild-type allele. Our results suggest that MCCA-R385S is a dominant negative allele and is biotin responsive in vivo.
authors.affiliation: Division of Metabolism and Molecular Pediatrics, University Children's Hospital, Zurich, Switzerland. Matthias.Baumgartner@kispi.unizh.ch
authors.forename: Matthias R
authors.initials: MR
authors.lastname: Baumgartner
authors.forename: M Fernanda
authors.initials: MF
authors.lastname: Dantas
authors.forename: Terttu
authors.initials: T
authors.lastname: Suormala
authors.forename: Shlomo
authors.initials: S
authors.lastname: Almashanu
authors.forename: Cecilia
authors.initials: C
authors.lastname: Giunta
authors.forename: Dolores
authors.initials: D
authors.lastname: Friebel
authors.forename: Boris
authors.initials: B
authors.lastname: Gebhardt
authors.forename: Brian
authors.initials: B
authors.lastname: Fowler
authors.forename: Georg F
authors.initials: GF
authors.lastname: Hoffmann
authors.forename: E Regula
authors.initials: ER
authors.lastname: Baumgartner
authors.forename: David
authors.initials: D
authors.lastname: Valle
mesh_terms: D000483:Alleles; D001483:Base Sequence; D001710:Biotin / Q000378:metabolism / Q000627:therapeutic use*; D019735:Carbon-Carbon Ligases / Q000172:deficiency* / Q000235:genetics*; D004252:DNA Mutational Analysis; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000378:metabolism; D015870:Gene Expression; D005822:Genetic Vectors / Q000235:genetics; D005858:Germany; D005998:Glycine / Q000031:analogs & derivatives* / Q000652:urine; D006115:Greece; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D028361:Mitochondrial Diseases / Q000188:drug therapy*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D014162:Transfection; D014631:Valerates / Q000652:urine
chemical_list: D014631:Valerates; C002163:beta-methylcrotonylglycine; C004961:beta-hydroxyisovaleric acid; D001710:Biotin; D019735:Carbon-Carbon Ligases; C021573:methylcrotonoyl-CoA carboxylase; D005998:Glycine