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Isolated 3-methylcrotonyl-CoA carboxylase (MCC) deficiency is an autosomal recessive disorder that appears to be the most frequent organic aciduria detected in tandem mass spectrometry (TMS)-based neonatal screening programs. The phenotype is variable, ranging from neonatal onset with severe neurological involvement to asymptomatic adults. MCC is a heteromeric mitochondrial enzyme composed of biotin containing alpha subunits and smaller beta subunits, encoded by MCCA and MCCB, respectively. We report mutation analysis in 28 MCC-deficient probands, 19 of whom were asymptomatic newborns detected by TMS newborn screening, and nine presented with clinical symptoms. Ten have mutations in MCCA, and 18 in MCCB. We identified 10 novel MCCA and 14 novel MCCB mutant alleles including missense, nonsense, frameshift and splice site mutations, and show that three of the missense mutations result in severely decreased MCC activity when expressed in MCC-deficient cell lines. Our data demonstrate no clear correlation between genotype and phenotype suggesting that factors other than the genotype at the MCC loci have a major influence on the phenotype of MCC deficiency.

A patient with a severe neonatal variant of 3-methylcrotonyl-CoA carboxylase (MCC) deficiency is reported. The first child of healthy consanguineous Turkish parents presented on the second day of life with dehydration, cyanosis, no sucking, generalized muscular hypotonia, encephalopathy, respiratory depression requiring mechanic ventilation, macrocephaly, severe acidosis and hypoglycaemia. Elevated C5-OH-carnitine in dried blood spot by tandem MS and elevated urinary excretion of 3-hydroxyisovaleric acid and 3-methylcrotonylglycine suggested MCC deficiency, confirmed by enzyme analysis in cultured fibroblasts. Cerebral ultrasonography and cranial CT findings revealed progressive changes such as disseminated encephalomalacia, cystic changes, ventricular dilatation and cerebral atrophy. Treatment with high-dose biotin and protein-restricted diet was ineffective and the patient died at the age of 33 days with progressive neurological deterioration. Mutation analysis revealed a homozygous mutation in the splice acceptor site of intron 15 in the MCC beta-subunit. Early-onset severe necrotizing encephalopathy should be included in the differential diagnosis of isolated MCC deficiency.

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.

Abstract-We have tested the hypothesis that increased gap junctional communication contributes to the augmented endothelium-dependent vasodilation in pregnancy. Contractile force and connexin43 expression were measured in aortic rings from nonpregnant and pregnant rats. Norepinephrine-constricted aortas from pregnant rats were more sensitive to acetylcholine, but not to sodium nitroprusside, compared with those from nonpregnant rats. Vessels from pregnant rats, constricted either with 45 mmol/L KCl or with norepinephrineϩ10 Ϫ4 mol/L N G -monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide synthase, also exhibited greater relaxation to acetylcholine. Heptanol, an uncoupler of gap junctional communication, inhibited acetylcholine responses in norepinephrine-constricted aortas from nonpregnant rats but greatly impaired acetylcholine relaxation in aortas from pregnant rats. Heptanol also inhibited in both groups acetylcholine responses in vessels constricted with KCl, only minimally affected acetylcholine relaxation in arteries constricted with norepinephrineϩL-NMMA, and did not change sodium nitroprusside-induced relaxation. Tetraethylammonium chloride induced greater contractions in control aortas compared with aortas from pregnant rats. Increased connexin43 mRNA levels were found in the uterus and in the mesenteric, uterine, and thoracic aortic arteries, but not in the heart and brain, from pregnant rats. These results suggest that increased gap junctional communication, possibly due to increased gap junction protein expression, may facilitate the effects of endothelium-derived relaxing factors, contributing to the augmented endothelium-dependent relaxation in arteries from pregnant rats. Key Words: preeclampsia Ⅲ rats Ⅲ gap junctions Ⅲ nitric oxide Ⅲ endothelium-derived factor P regnancy is associated with a decrease in systemic vascular resistance, which maintains or reduces maternal blood pressure despite the increase in plasma volume and cardiac output. 1 Pregnancy in women and in other mammals, such as the rat, is also characterized by a blunted pressor response 2,3 and decreased vascular reactivity 4,5 to a series of vasoconstrictors. The mechanism(s) responsible for these cardiovascular changes in pregnancy is not fully understood but has been under intense investigation, particularly because its malfunction may have a role in preeclampsia. 6 Because blunted constrictor responses in arteries from pregnant animals are observed in vitro 4,5 and no changes in receptor number or affinity seem to occur, 2,7 it has been suggested that a general mechanism, occurring within the blood vessel wall, is involved. Enhanced endothelium-dependent vasodilation, which may contribute to the attenuated vasoconstriction during pregnancy, has been systematically shown in vessels from pregnant animals, including the uterine, mesenteric, thoracic, and abdominal aortic arteries. 8 -11 Nitric oxide (NO), but not prostaglandins, is considered to contribute substantially to the increased endothelium-dependent relaxation in...

We report a 3-year-old boy with isolated 3-methylcrotonyl-coenzyme A deficiency with unexpectedly severe presentation, seizures and history of cerebral ischae-mic episode.

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