Evaluation of 3-methylcrotonyl-CoA carboxylase deficiency detected by tandem mass spectrometry newborn screening

Newborn screening and genetic diagnosis of 3-methylcrotonyl-CoA carboxylase deficiency in Quanzhou,China

Background and aims

3-Methylcrotonyl-CoA carboxylase deficiency (3-MCCD) is an autosomal recessive leucine catabolism condition caused by 3-methylcrotonyl-CoA carboxylase (3-MCC) deficiency due to MCCC1/MCCC2 variants. We investigated its incidence and features in Quanzhou, China.

Materials and methods

We screened 643,606 newborns (January 2014 to December 2022) for elevated 3-hydroxyisovalerylcarnitine (C5OH) levels using tandem mass spectrometry (MS/MS). Molecular analyses identified MCCC1/MCCC2 variants in suspected 3-MCCD cases.

Results

Seventeen neonates, two maternal patients, and one paternal patient had 3-MCCD. Its incidence in the Quanzhou study population was 1/37,859 newborns. All patients and neonates with 3-MCCD exhibited increased C5OH concentrations. Most patients [76.5%(13/17)] had increased urinary 3-methylcrotonylglycine (3-MCG) and 3-hydroxyisovaleric acid (3-HIVA) levels. Eight neonates and all adults with 3-MCCD had secondary carnitine deficiency. We identified seventeen variants, including 6 novel ones.MCCC1and MCCC2 variants were found in 47.1% and 52.9% of patients,with c.1331G > A (31.3%) and c.351_353delTGG (50.0%) being the most prevalent, respectively. Clinical symptoms were observed in 11.8% of patients.

Conclusion

We identified six new MCCC1/MCCC2 variants, enhancing our understanding of the 3-MCCD molecular profile. Secondary carnitine deficiency occurred in eight neonates and all adult patients. Although clinical symptoms were observed in 11.8% of patients, whether they were related to 3-MCCD remain unclear. Therefore, further studies are required to decide whether 3-MCCD and C5OH indicators should continue to be used.

Newborn screening for 3-methylcrotonyl-CoA carboxylase deficiency in Zhejiang province, China

BACKGROUND

3-Methylcrotonyl-CoA carboxylase deficiency (3-MCCD) is an autosomal recessive inborn defect of leucine catabolism caused by MCCC1 or MCCC2 variants. 3-MCCD is considered to be a relatively benign disorder with favorable outcome. We report the biochemical, clinical, and molecular features of patients with 3-MCCD.

METHODS

From January 2009 to August 2022, 4,402,587 newborns were screened by tandem mass spectrometry. Newborns with increased C5OH concentrations were recalled for repeated testing, urine organic acid analysis and molecular genetic analysis were performed if the second test was still positive.

RESULTS

A total of 53 patients were diagnosed with 3-MCCD. The estimated incidence of 3-MCCD in Zhejiang Province was 1 in 83,068 newborns. All these 53 patients exhibited increased C5OH concentrations in blood. 94 % (50/53) of the patients had markedly increased urinary 3-hydroxyisovaleric acid and 3-methylcrotonylglycine. All these 53 patients did not present any clinical symptom. Twenty-three of 53 patients had secondary carnitine deficiency. Twenty-eight patients had variants in MCCC1 and 25 had variants in MCCC2. Eleven novel variants were found in MCCC1 and MCCC2. The c.639 + 2 T > A and c.1144-1147delinsTTTT were the most common variant in MCCC1 and MCCC2 gene, respectively.

CONCLUSION

We elucidated the incidence of 3-MCCD in Zhejiang province, China. All patients showed asymptomatic and present normal growth and development during follow-up. Eleven novel MCCC1 and MCCC2 variants were identified, which expanded the variant spectrum.

Partial Biotinidase Deficiency Revealed Imbalances in Acylcarnitines Profile at Tandem Mass Spectrometry Newborn Screening

Biotinidase (BTD) deficiency is an autosomal recessive inherited neurocutaneous disorder. BTD recycles the vitamin biotin, a coenzyme essential for the function of four biotin-dependent carboxylases, including propionyl-CoA carboxylase, 3-methylcrotonyl-CoA carboxylase, pyruvate carboxylase, and acetyl-CoA carboxylase. Due to deficient activities of the carboxylases, BTD deficiency is also recognized as late-onset multiple carboxylase deficiency and is associated with secondary alterations in the metabolism of amino acids, carbohydrates, and fatty acids. BTD deficiency can be classified as "profound", with less than 10% of mean normal activity, and as "partial" with 10-30% of mean normal activity. Newborn screening (NBS) of BTD deficiency is performed in most countries and is able to detect both variants. Moreover, mild metabolic alterations related to carboxylase deficiency in profound BTD deficiency could result and possibly be revealed in the metabolic profile by tandem mass spectrometry (MS/MS) NBS. Here, we report the case of a newborn female infant with an initial suspected BTD deficiency at the NBS test, finally confirmed as a partial variant by molecular testing. Although BTD deficiency was partial, interestingly her metabolic profile at birth and during the follow-up tests revealed, for the first time, alterations in specific acylcarnitines as a possible result of the deficient activity of biotin-dependent carboxylases.

3-Methylcrotonyl-CoA carboxylase deficiency newborn screening in a population of 536,008: is routine screening necessary?

Objective To evaluate whether 3-methylcrotonyl-CoA carboxylase deficiency (3-MCCD) should be routinely screened in newborns. Methods Dried blood spots (DBS) were collected and analyzed by tandem mass spectrometry (TMS). Blood samples were collected from infants with positive 3-MCCD results. Targeted sequencing was performed using the extended panel for inherited metabolic diseases to detect 306 genes. The sequencing libraries were quantified and used for massively parallel sequencing on the Illumina HiSeq 2500 platform. Results A total of 536,008 infants underwent newborn screening (NBS) and 14 cases of 3-MCCD were diagnosed. The incidence of 3-MCCD in Jiangsu province was 1:38,286. During the last 3 years of follow-up, none of the subjects with 3-MCCD exhibited obvious clinical symptoms. Only two children had mild feeding difficulties and vomiting. Eleven patients had complex variants of the MCCC1 gene, and three patients had mutations in MCCC2. In total, 17 types of MCCC1 or MCCC2 variants were found, and c.639 + 2t > a was the most common mutation. Conclusions As far as the current results are concerned, 3-MCCD may be benign in Jiangsu province. However, additional investigations and a longer follow-up period are necessary to decide whether NBS of 3-MCCD is necessary or not.

Association of prehypertension and hyperhomocysteinemia with subclinical atherosclerosis in asymptomatic Chinese: a cross-sectional study

OBJECTIVES

Comorbid hypertension and hyperhomocysteinemia is an important risk factor for carotid atherosclerotic plaque formation. We put forward the hypothesis that the subjects with comorbid prehypertension and hyperhomocysteinemia also had an increased risk of subclinical atherosclerosis, using carotid intima-media thickness (CIMT) as the marker of the atherosclerotic process.

METHODS

A total of 4102 asymptomatic Chinese subjects aged 18-60 years were divided into four groups according to blood pressure (BP) and homocysteine (HCY) level: the control group without prehypertension or hyperhomocysteinemia, isolated prehypertension group, simple hyperhomocysteinemia group and prehypertension with hyperhomocysteinemia group. Serum lipids, fasting blood glucose (FBG), HCY and CIMT were measured.

RESULTS

There was significant difference in the positive rates of increased CIMT among four groups. Compared with the controls, the subjects in the other three groups had a higher risk of increased CIMT (isolated prehypertension group, OR 2.049, 95% CI 1.525 to 2.754; simple hyperhomocysteinemia group, OR 2.145, 95% CI 1.472 to 3.125; prehypertension and hyperhomocysteinemia group, OR 3.199, 95% CI 2.362 to 4.332). However, by multiple logistic regression analysis, only comorbid prehypertension and hyperhomocysteinemia was independently associated with increased CIMT (OR 1.485, 95% CI 1.047 to 2.108, P<0.05).

CONCLUSIONS

Comorbid prehypertension and hyperhomocysteinemia was an independent risk factor of subclinical atherosclerosis in asymptomatic Chinese, but isolated prehypertension or hyperhomocysteinemia was not. Therefore, combined intervention for prehypertension and hyperhomocysteinemia may contribute to decrease the incident of cardiovascular disease.

Maternal 3-methylcrotonyl-coenzyme A carboxylase deficiency with elevated 3-hydroxyisovalerylcarnitine in breast milk

We report here a case of maternal 3-methylcrotonyl-coenzyme A carboxylase (3-MCC) deficiency in a Korean woman. Her 2 infants had elevated 3-hydroxyisovalerylcarnitine (C5-OH) on a neonatal screening test by liquid chromatography-tandem mass spectrometry (LC-MS/MS), but normal results were found on urine organic acid analysis. The patient was subjected to serial testing and we confirmed a maternal 3-MCC deficiency by blood spot and breast milk spot test by LC-MS/MS, serum amino acid analysis, urine organic acid and molecular genetic analysis that found c.838G>T (p.Asp280Tyr) homozygous mutation within exon 9 of the MCCB gene. Especially, we confirmed marked higher levels of C5-OH on breast milk spot by LC-MS/MS, in the case of maternal 3-MCC deficiency vs. controls.

3-Methylcrotonyl-CoA carboxylase deficiency: Mutational spectrum derived from comprehensive newborn screening

The deficiency of 3-methycrotonyl-CoA carboxylase (3-MCC; EC 6.4.1.4) is an autosomal recessive organic aciduria that is included in the newborn screening programs of several countries. This study reports data mainly obtained from the Portuguese newborn screening program collected over a ten-year period. Analysis of the MCCC1 and MCCC2 genes yielded 26 previously unreported mutations and a variant of clinically unknown significance. These mutations are discussed in the context of their likely impact on the function of the 3-MCC enzyme, with a view to exploring whether a phenotype-genotype correlation might be discerned. Further, these mutations were analysed in the context of what is known of the MCCC1 and MCCC2 mutational spectra, information that will be useful in both clinical and laboratory practice.

Primary and maternal 3-methylcrotonyl-CoA carboxylase deficiency: insights from the Israel newborn screening program

BACKGROUND

3-Methylcrotonyl-CoA carboxylase deficiency (3MCCD) is an inborn error of leucine catabolism. Tandem mass spectrometry newborn screening (NBS) programs worldwide confirmed 3MCCD to be the most common organic aciduria and a relatively benign disorder with favorable outcome. In addition, several asymptomatic 3MCCD mothers were initially identified following abnormal screening of their healthy babies and were appropriately termed maternal 3MCCD.

METHODS

This is a retrospective study that summarizes all the clinical, biochemical, and genetic data collected by questionnaires of all 3MCCD individuals that were identified by the extended Israeli NBS program since its introduction in 2009 including maternal 3MCCD cases.

RESULTS

A total of 36 3MCCD subjects were diagnosed within the 50-month study period; 16 were classified primary and 20 maternal cases. Four additional 3MCCD individuals were identified following sibling screening. All maternal 3MCCD cases were asymptomatic except for one mother who manifested childhood hypotonia. Most of the primary 3MCCD individuals were asymptomatic except for two whose condition was also complicated by severe prematurity. Initial dried blood spot (DBS) free carnitine was significantly lower in neonates born to 3MCCD mothers compared with newborns with primary 3MCCD (p = 0.0009). Most of the mutations identified in the MCCC1 and MCCC2 genes were missense, five of them were novel.

CONCLUSIONS

Maternal 3MCCD is more common than previously thought and its presence may be initially indicated by low DBS free carnitine levels. Our findings provide additional confirmation of the benign nature of 3MCCD and we suggest to exclude this disorder from NBS programs.

Newborn screening

Newborn screening is a major aspect of public health success. Babies in every state are tested for a recommended uniform screening panel of conditions not otherwise immediately evident in the first days of life. With the goal of reducing morbidity and mortality, conditions should be added to newborn screening panels using a scientific, evidence-based process. Newborn screening is a system involving partners at many levels; neonatologists have a special role in ensuring that their vulnerable patients also receive this life-saving test. Careful attention to the social, legal, and ethical aspects will help increase the scope of newborn screening.

An asymptomatic mother diagnosed with 3-methylcrotonyl-CoA carboxylase deficiency after newborn screening

BACKGROUND

3-Methylcrotonyl-CoA carboxylase (3-MCC) deficiency is an autosomal recessively inherited disease of leucine catabolism. It is the most commonly observed organic acidemia where tandem mass spectrometry can be performed in newborn screening. The clinical phenotypes may differ from neurological involvement in newborns to asymptomatic adults. Diagnosis is made by increased 3-hydroxyisovaleric acid in blood and 3-methylcrotonylglycine in urine.

CASE REPORT

We would like to present an interesting case of a 32-year-old asymptomatic mother, who was investigated metabolically and diagnosed with 3-MCC deficiency, after a 7-day-old healthy baby referred to our unit with the preliminary diagnosis of organic academia during her extended newborn screening.

RESULTS

All of the metabolic findings of the baby were normal except for very low carnitine levels. Her mother's total and free carnitine levels were also extremely low. Urine organic acid analysis revealed excessively increased 3-methylcrotonylglycine and 3-hydroxyisovaleric acid. Acylcarnitine profile showed markedly elevated C5 hydroxy 3 hydroxyisovalerylcarnitine and decreased C2 acetylcarnitine. In order to confirm the diagnosis of 3-methylcrotonylglycinuria, molecular analysis was done, and IVS3-1G>C/p.T556I compound heterozygote mutation was detected. p.T556I is a novel mutation.

CONCLUSION

We would like to emphasize performing extended metabolic investigations in case of suspicion of metabolic disease in order to diagnose metabolic diseases both in babies and in asymptomatic mothers.

Abnormal Newborn Screening in a Healthy Infant of a Mother with Undiagnosed Medium-Chain Acyl-CoA Dehydrogenase Deficiency

A neonate with low blood free carnitine level on newborn tandem mass spectrometry screening was evaluated for possible carnitine transporter defect (CTD). The plasma concentration of free carnitine was marginally reduced, and the concentrations of acylcarnitines (including C6, C8, and C10:1) were normal on confirmatory tests. Organic acids in urine were normal. In addition, none of the frequent Faroese SLC22A5 mutations (p.N32S, c.825-52G>A) which are common in the Danish population were identified. Evaluation of the mother showed low-normal free carnitine, but highly elevated medium-chain acylcarnitines (C6, C8, and C10:1) consistent with medium-chain acyl-CoA dehydrogenase deficiency (MCADD). The diagnosis was confirmed by the finding of homozygous presence of the c.985A>G mutation in ACADM.

Is L-Carnitine Supplementation Beneficial in 3-Methylcrotonyl-CoA Carboxylase Deficiency?

BACKGROUND

3-Methylcrotonyl-CoA carboxylase deficiency (3-MCCd) is an autosomal recessive disorder in the catabolism of leucine. In the present study, we investigated the current and prior medical condition of patients with 3-MCCd in the Faroe Islands and their carnitine levels in blood, urine and muscle tissue with and without L-carnitine supplementation to evaluate the current treatment strategy of not recommending L-carnitine supplementation to Faroese 3-MCCd patients.

METHODS

Blood and urine samples and muscle biopsies were collected from patients at inclusion and at 3 months. Eight patients received L-carnitine supplementation when recruited; five did not. Included patients who received supplementation were asked to stop L-carnitine, the others were asked to initiate L-carnitine supplementation during the study. Symptoms were determined by review of hospital medical records and questionnaires answered at baseline and after the intervention.

RESULTS

The prevalence of 3-MCCd in the Faroe Islands was 1:2,400, the highest reported worldwide. All patients were homozygous for the MCCC1 mutation c.1526delG. When not administered L-carnitine, the 3-MCCd patients (n = 13) had low plasma and muscle free carnitine levels, 6.9 (SD 1.4) μmol/L and 785 (SD 301) nmol/g wet weight, respectively. L-Carnitine supplementation increased muscle and plasma carnitine levels to a low-normal range, 25.5 (SD 10.9) μmol/L and 1,827 (SD 523) nmol/g wet weight, p < 0.01, respectively. Seven of the thirteen 3-MCCd subjects suffered from self-reported fatigue with some alleviation after L-carnitine supplementation.

CONCLUSION

3-MCCd is common in the Faroe Islands. Some symptomatic 3-MCCd patients may benefit biochemically and clinically from L-carnitine supplementation, a more general recommendation cannot be given.

Consanguinity and rare mutations outside of MCCC genes underlie nonspecific phenotypes of MCCD

Purpose

3-Methylcrotonyl-CoA carboxylase deficiency (MCCD) is an autosomal recessive disorder of leucine catabolism that has a highly variable clinical phenotype, ranging from acute metabolic acidosis to nonspecific symptoms such as developmental delay, failure to thrive, hemiparesis, muscular hypotonia, and multiple sclerosis. Implementation of newborn screening for MCCD has resulted in broadening the range of phenotypic expression to include asymptomatic adults. The purpose of this study was to identify factors underlying the varying phenotypes of MCCD.

Methods

We performed exome sequencing on DNA from 33 cases and 108 healthy controls. We examined these data for associations between either MCC mutational status, genetic ancestry, or consanguinity and the absence or presence/specificity of clinical symptoms in MCCD cases.

Results

We determined that individuals with nonspecific clinical phenotypes are highly inbred compared with cases that are asymptomatic and healthy controls. For 5 of these 10 individuals, we discovered a homozygous damaging mutation in a disease gene that is likely to underlie their nonspecific clinical phenotypes previously attributed to MCCD.

Conclusion

Our study shows that nonspecific phenotypes attributed to MCCD are associated with consanguinity and are likely not due to mutations in the MCC enzyme but result from rare homozygous mutations in other disease genes.

Asymptomatic maternal 3-methylcrotonylglycinuria detected by her unaffected baby's neonatal screening test

3-methylcrotonyl-coenzyme A carboxylase (3MCC) deficiency is an autosomal recessive disorder in which leucine catabolism is hampered, leading to increased urinary excretion of 3-methylcrotonylglycine. In addition, 3-hydroxyisovalerylcarnitine levels increase in the blood, and the elevated levels form the basis of neonatal screening. 3MCC deficiency symptoms are variable, ranging from neonatal onset with severe neurological abnormality to a normal, asymptomatic phenotype. Although 3MCC deficiency was previously considered to be rare, it has been found to be one of the most common metabolic disorders in newborns after the neonatal screening test using tandem mass spectrometry was introduced. Additionally, asymptomatic 3MCC deficient mothers have been identified due to abnormal results of unaffected baby's neonatal screening test. Some of the 3MCC-deficient mothers show symptoms such as fatigue, myopathy, or metabolic crisis with febrile illnesses. In the current study, we identified an asymptomatic 3MCC deficient mother when she showed abnormal results during a neonatal screening test of a healthy infant.

Biotin and carnitine profiles in preterm infants in Japan

BACKGROUND

Biotin plays an important role as a covalently bound coenzyme for carboxylases. Carnitine is essential in β-oxidation to transport long-chain fatty acids across the inner mitochondrial membrane. The present study was conducted to assess the risk of biotin and carnitine deficiencies in preterm infants who received enteral feeding with maternal milk and/or standard infant formula made in Japan.

METHODS

Forty-six infants were enrolled in the study. Urine and serum samples and dried blood spots were collected at 1 week and 1 month of age. Additionally, samples were collected at 40 and 44 weeks post-menstrual age (PMA) in preterm infants. Free carnitine and C5-OH acylcarnitine, which consist of 3-hydroxyisovalerylcarnitine as a major isomer, were measured in serum samples and dried blood spots using tandem mass spectrometry. Urine 3-hydroxyisovaleric acid (3-HIVA) was measured using gas chromatography/mass spectrometry.

RESULTS

The free carnitine levels in preterm infants were significantly lower than those in term infants, but increased with PMA in serum samples and dried blood spots. C5-OH acylcarnitine and urinary 3-HIVA levels, which were very low in term infants, were increased with PMA in preterm infants.

CONCLUSION

The present results may indicate chronic biotin deficiency in preterm infants fed maternal milk and/or standard infant formula. Analyses of carnitine profiles of dried blood spots and urine 3-HIVA are relatively non-invasive and useful for the early detection of biotin deficiency in preterm infants.

Outcome of infants diagnosed with 3-methyl-crotonyl-CoA-carboxylase deficiency by newborn screening

INTRODUCTION

3-Methyl CoA carboxylase (3-MCC) deficiency is an inborn error of metabolism in the catabolism of the amino acid leucine. Original reports suggested this disorder was associated with significant neurological and biochemical effects. However newborn screening has identified a higher than expected incidence of this disorder with apparent normal outcome in most cases.

METHOD

A retrospective analysis of thirty-five cases of 3-MCC deficiency identified by newborn screening and diagnosed by enzyme or molecular analysis.

RESULTS

There was a strong inverse correlation between initial C5OH level and residual enzyme activity. A few reports of hypoglycemia, ketosis, poor feeding/failure to thrive or fasting intolerance were reported, but there was no clear relationship between symptoms and residual enzyme activity. Developmental outcome included several children with mental retardation (including one with Down syndrome and one with schizencephaly) and two with Autism Spectrum disorders but there was no apparent relationship to residual enzyme activity. Free carnitine deficiency was relatively common.

DISCUSSION

Although residual enzyme activity was clearly related to metabolite elevation, there was no apparent relationship with other measures of outcome. The number of reports of neurologic abnormalities or metabolic symptoms (poor feeding, hypoglycemia, fasting intolerance, etc.) is concerning, but the significance is unclear in this retrospective sample.

3-methylcrotonyl-CoA carboxylase deficiency: clinical, biochemical, enzymatic and molecular studies in 88 individuals

Background

Isolated 3-methylcrotonyl-CoA carboxylase (MCC) deficiency is an autosomal recessive disorder of leucine metabolism caused by mutations in MCCC1 or MCCC2 encoding the α and β subunit of MCC, respectively. The phenotype is highly variable ranging from acute neonatal onset with fatal outcome to asymptomatic adults.

Methods

We report clinical, biochemical, enzymatic and mutation data of 88 MCC deficient individuals, 53 identified by newborn screening, 26 diagnosed due to clinical symptoms or positive family history and 9 mothers, identified following the positive newborn screening result of their baby.

Results

Fifty-seven percent of patients were asymptomatic while 43% showed clinical symptoms, many of which were probably not related to MCC deficiency but due to ascertainment bias. However, 12 patients (5 of 53 identified by newborn screening) presented with acute metabolic decompensations. We identified 15 novel MCCC1 and 16 novel MCCC2 mutant alleles. Additionally, we report expression studies on 3 MCCC1 and 8 MCCC2 mutations and show an overview of all 132 MCCC1 and MCCC2 variants known to date.

Conclusions

Our data confirm that MCC deficiency, despite low penetrance, may lead to a severe clinical phenotype resembling classical organic acidurias. However, neither the genotype nor the biochemical phenotype is helpful in predicting the clinical course.

Extended newborn screening: an update for the general paediatrician

Extended newborn screening (ENBS) with the use of tandem mass spectrometry technology is well established in all Australian states and in New Zealand. ENBS has afforded a marked reduction in morbidity and mortality in select conditions such as medium-chain acyl-CoA dehydrogenase deficiency. While this technology has been of great benefit to newborn screening, it comes with many inherent and unforeseen challenges. In this review, we discuss the successes and challenges associated with ENBS.

Uneventful clinical courses of Korean patients with methylcrotonylglycinuria and their common mutations

Methylcrotonylglycinuria (MCG) is an inborn error of leucine catabolism and results from the deficiency of 3-methylcrotonyl-CoA carboxylase. Patients with MCG show a highly variable clinical phenotype, ranging from asymptomatic to severe. With the introduction of newborn screening using tandem mass spectrometry, most patients with MCG are identified in their asymptomatic neonatal periods. Owing to their fair clinical outcomes, there exists a controversy over the need for aggressive medical intervention or even for newborn screening for MCG. Our study, reporting 11 Korean MCG patients from nine unrelated families, who were identified by newborn screening or family member testing and normally developed without experiencing an metabolic crisis during the follow-up period of 2.6±1.96 years (range, 1-10 years), indicates that the aggressive medical intervention might not be needed at least for the MCG patients identified by screening program in asymptomatic period. A total of six MCCC2 mutations, but no MCCC1 mutation, were identified in 17 of 18 alleles (94.4%). p.D280Y was identified in the 12/18 alleles (66.7%), indicating a founder effect. Moreover, the rest five variants, p.S342K, p.Q496H, p.P552S, p.T556A and p.P459S, were all previously unreported. The results of our study indicate that the distinct molecular genetic characteristics exist in Korean MCG patients.

Positive newborn screen in a normal infant of a mother with asymptomatic very long-chain Acyl-CoA dehydrogenase deficiency

A neonate with elevated tetradecenoylcarnitine (C14:1) on the newborn screen was evaluated for possible very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) and found to be a carrier. However, his symptom-free mother was subsequently diagnosed with VLCADD. This documents maternal VLCADD causing a positive newborn screening result in an offspring.

Update on investigating hypoglycaemia in childhood

Identification and investigation of hypoglycaemia in childhood remains an important clinical emergency. Rapid recognition and appropriate management of this clinical state continues to be important in order to prevent neurological damage or even death. The purpose of this review is to provide an update on the advances made in this area since the review by Bonham in this journal in 1993. Advances in molecular science and diagnostic techniques have assisted in understanding the mechanisms involved in the homeostasis of glucose metabolism at rest and when stressed. New disorders causing hypoglycaemia are described using the classification based upon aetiologies, which was used in Bonham's original paper. The development and use of guidelines and pre-assembled packs for investigating hypoglycaemia is also discussed.

Elevated neonatal 3-OH isovalerylcarnitine due to breast milk sources in maternal 3-MCC deficiency

We report a positive newborn screen for 3-hydroxyisovalerylcarnitine (C(5)OH) with an absence of 3-methylcrotonyl-coenzyme A carboxylase deficiency in the neonate. Subsequent blood tests demonstrated persistently elevated C(5)OH. Serial testing of the mother identified markedly elevated C(5)OH in both maternal blood and breast milk. High C(5)OH milk concentrations provide a significant source of C(5)OH to the nursing neonate and possibly explains its persistent elevation in the neonate, a commonly observed finding in maternal 3-MCC deficiency.

Serum total homocysteine, folate, 5,10-methylenetetrahydrofolate reductase (MTHFR) 677C-->T genotype and subclinical atherosclerosis

OBJECTIVE

To determine the relationship of serum total homocysteine (tHcy), serum folate and 5,10-methylenetetrahydrofolate reductase (MTHFR) 677C-->T genotype with ultrasonic arterial wall measurements associated with subclinical atherosclerosis.

STUDY DESIGN

Cross-sectional analysis of 767 participants in an ongoing prospective study. Intima-media thickness (IMT) of the common carotid (IMTcc), IMT of the internal carotid including plaque when present (IMT(max)) and the sum of the thickest plaques present in both carotid and both common femoral bifurcations (total plaque thickness (TPT)) were measured using ultrasound.

RESULTS

People in the upper homocysteine quartile were more likely to have clinical cardiovascular disease (CVD) than those in the lowest three quartiles. They were also more likely to have plaques. The MTHFR 677C-->T genotype was not associated with any of the measures of subclinical atherosclerosis in either men or women but was the most important determinant of total homocysteine levels in men under 60 years of age.

CONCLUSIONS

Increased homocysteine levels but not MTHFR 677C-->T genotype, are associated with subclinical atherosclerosis and the presence of plaques. Our results indicate that measurements of blood levels of homocysteine and folate in people at intermediate risk for atherosclerotic CVD before symptoms occur, might improve risk stratification and facilitate the decision to provide folate/B vitamin intervention in primary prevention.

Maternal glutaric acidemia, type I identified by newborn screening

We report two women with glutaric acidemia type I in whom the diagnosis was unsuspected until a low carnitine level was found in their newborn children. Both mothers had low carnitine in plasma. In the first, organic acid analysis was only done after fibroblast studies revealed normal carnitine uptake. Having learned from the first family, organic acid analysis was done immediately in the mother of family 2. In both, the plasma acylcarnitine profile was normal but both excreted the metabolites typical of their disorder. One of the women was a compound heterozygote for distinct mutations in the glutaric acid dehydrogenase gene, whereas the second was either homozygous or hemizygous for a mutation in Exon 6 of the gene.

Potential misdiagnosis of 3-methylcrotonyl-coenzyme A carboxylase deficiency associated with absent or trace urinary 3-methylcrotonylglycine

We report 2 patients with isolated 3-methylcrotonyl-coenzyme A carboxylase deficiency whose urine was devoid of, or contained only trace, 3-methylcrotonylglycine, the pathognomonic marker for this disorder. The first patient, a girl with trisomy 21, was detected through newborn screening with an elevated 5 carbon hydroxycarnitine species level, and the second patient came to clinical attention at the age of 5 months because of failure to thrive and developmental delay. Investigation of urinary organic acids revealed an elevated 3-hydroxyisovaleric acid level but no demonstrable 3-methylcrotonylglycine in both patients. Enzyme studies in cultured fibroblasts confirmed isolated 3-methylcrotonyl-coenzyme A carboxylase deficiency with residual activities of 5% to 7% and 12% of the median control value, respectively. Incorporation of 14C-isovaleric acid into intact fibroblasts was essentially normal, showing that the overall pathway was at least partially functional and potentially explaining the absence of 3-methylcrotonylglycine in urine. Mutation analysis of the MCCA and MCCB genes revealed that both patients were compound heterozygous for a missense mutation, MCCB-c.1015G-->A (p.V339M), and a second mutation that leads to undetectable MCCB messenger (poly A+) RNA. Absent or trace 3-methylcrotonylglycine levels in urine raises the potential for misdiagnosis in the clinical biochemical genetics laboratory based solely on urine organic acid analysis using combined gas chromatography-mass spectrometry.

Circulating homocysteine and large arterial stiffness and thickness in a population-based sample of middle-aged and elderly men

Elevated plasma homocysteine (tHcy) is considered as a risk factor for cardiovascular events, and has been associated with arterial stiffness and subclinical atherosclerosis in subjects with classical cardiovascular risk factors. The aim of this study is to investigate the association of plasma tHcy with functional and structural changes in the large arteries by measuring aortic pulse-wave velocity (PWV) and carotid artery intima-media thickness (CIMT). In a population-based sample of 376 middle-aged and elderly men, tHcy levels were measured by using fluorescence polarization immunoassay. Aortic stiffness was assessed non-invasively by measuring carotid-femoral PWV with the use of applanation tonometry. CIMT was measured by ultrasonography. We used multivariate linear regression analysis with the log-transformed value of tHcy as the determinant, and aortic PWV and CIMT as outcomes. In the univariate model, PWV increased with increasing tHcy concentration; PWV increased by 2.64 m/s (95% confidence interval (CI) 1.74; 3.54) per unit change in log tHcy. After adjustment for confounders, no statistically significant association remained; PWV increased by 0.42 m/s (95% CI -0.27; 1.11) per unit change in log tHcy. Furthermore, in the univariate model, CIMT increased significantly with increasing tHcy concentration; CIMT increased by 0.19 mm (95% CI 0.11; 0.26) per unit increase log tHcy. This association was attenuated and did not remain significant after additional adjustment for age and cardiovascular confounders (beta=0.06 (95% CI -0.01; 0.13)). The results of this study do not support the presence of an independent relationship between circulating tHcy levels and large artery stiffness and thickness.

Recent advances in newborn screening

The introduction of tandem mass spectrometry has unquestionably been the most striking recent advance in newborn screening. A single test is applied for the simultaneous diagnosis of a number of disorders, making it possible to screen for some disorders that might otherwise have seemed too rare. Current screening is for disorders of metabolism of amino acids, organic acids and fatty acids. Assay performance for detection of disorders appears very good, but rarity of disorders, varied definitions and systems for follow-up and lack of databases for inborn errors of metabolism diagnosed clinically means that there is as yet insufficient information about most disorders. The technology can be applied to a much wider range of compounds, and the field looks set to expand. A key feature of newborn screening programmes must be the assessment of outcomes, and a major reason for the lack of uniformity in the approach adopted in different countries is the paucity of information on this. The available evidence points to overall advantages flowing from early diagnosis by screening, with reduction in mortality and morbidity. More studies are clearly needed and some are under way. The next new group of disorders already proposed for newborn screening is the lysosomal storage disorders. Attitudes may be changing about what it is desirable to include in a newborn screening programme, and this will indeed pose new ethical dilemmas.

Expanded newborn screening identifies maternal primary carnitine deficiency

Primary carnitine deficiency impairs fatty acid oxidation and can result in hypoglycemia, hepatic encephalopathy, cardiomyopathy and sudden death. We diagnosed primary carnitine deficiency in six unrelated women whose unaffected infants were identified with low free carnitine levels (C0) by newborn screening using tandem mass spectrometry. Given the lifetime risk of morbidity or sudden death, identification of adult patients with primary carnitine deficiency is an added benefit of expanded newborn screening programs.

Carnitine-esters from the mushroom Suillus laricinus

Carnitine-esters (1-8) including, a compound (R)-3-hydroxybutanoyl-(R)-carnitine (5), were isolated from the mushroom Suillus laricinus. Their structures were determined by spectroscopic analyses and by total synthesis. One of these, (R)-3-hydroxy-2-methylpropanoyl-(R)-carnitine (4), promoted hyaluronan-degradation by human skin fibroblasts.

3-Methylcrotonyl-CoA carboxylase deficiency: metabolic decompensation in a noncompliant child detected through newborn screening

We report a 19-month-old girl with a 3-methylcrotonyl-coenzyme A carboxylase deficiency that was detected through newborn screening. She was treated for the first 12 months but was lost to follow-up after the initial year. Her parents did not comply with the recommendations for management during periods of illness or for regular medical evaluations. During an acute illness, she presented with severe acidosis, hypoglycemia, and a low plasma carnitine level at 19 months of age. This report highlights the importance of more extensive follow-up plans to improve parental compliance.

Principal component analysis of urine metabolites detected by NMR and DESI–MS in patients with inborn errors of metabolism

Urine metabolic profiles of patients with inborn errors of metabolism were examined with nuclear magnetic resonance (NMR) and desorption electrospray ionization mass spectrometry (DESI-MS) methods. Spectra obtained from the study of urine samples from individual patients with argininosuccinic aciduria (ASA), classic homocystinuria (HCY), classic methylmalonic acidemia (MMA), maple syrup urine disease (MSUD), phenylketonuria (PKU) and type II tyrosinemia (TYRO) were compared with six control patient urine samples using principal component analysis (PCA). Target molecule spectra were identified from the loading plots of PCA output and compared with known metabolic profiles from the literature and metabolite databases. Results obtained from the two techniques were then correlated to obtain a common list of molecules associated with the different diseases and metabolic pathways. The combined approach discussed here may prove useful in the rapid screening of biological fluids from sick patients and may help to improve the understanding of these rare diseases.

Mitochondrial targeting signals and mature peptides of 3-methylcrotonyl-CoA carboxylase

Inherited deficiency of 3-methylcrotonyl-CoA carboxylase (MCC), an enzyme of leucine degradation, is an organic acidemia detectable by expanded newborn screening with a variable phenotype that ranges from asymptomatic to death in infancy. Here, we show that the two subunits of the enzyme (MCCalpha; MCCbeta) are imported into the mitochondrial matrix by the classical pathway involving cleavable amino-terminal targeting presequences. We identified the cleavage sites (Tyr41/Thr42 and Ala22/Tyr23 for MCCalpha and MCCbeta, respectively) of the targeting signals and the amino-termini of the mature polypeptides of MCC and propionyl-CoA carboxylase, a mitochondrial paralog. The amino-termini containing 39 (MCCalpha) or 20 amino acids (MCCbeta) were both necessary and sufficient for targeting. Structural requirements for mitochondrial import were defined by site-directed mutagenesis. Our studies provide the prerequisite to understand the impact of specific mutations on the clinical phenotype of MCC deficiency.

Biochemical findings in common inborn errors of metabolism

The application of tandem mass spectrometry (MS/MS) to newborn screening has led to the detection of patients with a wider spectrum of inborn errors of metabolism. A definitive diagnosis can often be established early enough to start treatment before symptoms appear. Here, we review common biochemical findings in disorders caused by deficiency of 3-methylcrotonyl-CoA carboxylase, isobutyryl-CoA dehydrogenase, 2-methyl-3-hydroxybutyryl-CoA dehydrogenase, 3-ketothiolase, 2-methylbutyryl-CoA dehydrogenase, and medium chain acyl CoA dehydrogenase. The diagnosis of these disorders requires biochemical confirmation by measurement of plasma acylcarnitine profile, urine organic acids, and urine acylglycine profiles followed by measurement of enzyme activity or detection of causative mutations. Early treatment can improve the outcome of these disorders.

The tandem mass spectrometry newborn screening experience in North Carolina: 1997-2005

North Carolina (NC) was the first US state to initiate universal tandem mass spectrometry (MS/MS) newborn screening. This began as a statewide pilot project in 1997 to determine the incidence and feasibility of screening for fatty acid oxidation, organic acid and selected amino acid disorders. The MS/MS analyses were done by a commercial laboratory and all follow-up and confirmatory testing was performed through the NC Newborn Screening (NBS) Program. In April 1999, the NC NBS Laboratory began the MS/MS analyses in-house. Between 28 July 1997 and 28 July 2005, 944,078 infants were screened and 219 diagnoses were confirmed on newborns with elevated screening results, for an overall incidence of 1:4,300. Ninety-nine infants were identified with fatty acid oxidation disorders, 58 with organic acidaemias and 62 with aminoacidopathies. Medium-chain acyl-CoA dehydrogenase deficiency, 3-methylcrotonyl-CoA carboxylase deficiency and disorders of phenylalanine metabolism were the most common disorders detected. Identification of affected infants has allowed retrospective testing of other family members, resulting in an additional 16 diagnoses. Seven neonates died from complications of their metabolic disorders/prematurity despite timely MS/MS screening. In addition, there were six infants who were not identified by elevated NBS results but who presented with symptoms later in infancy. The NC MS/MS NBS Program uses a two-tier system, categorizing results as either 'borderline' or 'diagnostic' elevated, for both the cutoffs and follow-up protocol. Infants with an initial borderline result had only a repeat screen. Infants with a diagnostic or two borderline results were referred for confirmatory testing. The positive predictive value of the NC MS/MS NBS for those infants requiring confirmatory testing was 53% for 2003 and 2004. The success of the NC MS/MS NBS Program in identifying infants with metabolic disorders was dependent on a comprehensive follow-up protocol integrating the public health laboratory and the academic metabolic centres.

Newborn screening for 3-methylcrotonyl-CoA carboxylase deficiency: population heterogeneity ofMCCA andMCCB mutations and impact on risk assessment

New technology enables expansion of newborn screening (NBS) of inborn errors aimed to prevent adverse outcome. In conditions with a large share of asymptomatic phenotypes, the potential harm created by NBS must carefully be weighed against benefit. Policies vary throughout the United States, Australia, and Europe due to limited data on outcome and treatability of candidate screening conditions. We elaborated the rationale for decision making in 3-methylcrotonyl-coenzyme A (CoA) carboxylase deficiency (MCCD), which afflicts leucine catabolism, with reported outcomes ranging from asymptomatic to death. In Bavaria, we screened 677,852 neonates for 25 conditions, including MCCD, based on elevated concentrations of 3-hydroxyisovalerylcarnitine (3-HIVA-C). Genotypes of MCCA (MCCC1) and MCCB (MCCC2) were assessed in identified newborns, their relatives, and in individuals (n = 17) from other regions, and correlated to biochemical and clinical phenotypes. NBS revealed eight newborns and six relatives with MCCD, suggesting a higher frequency than previously assumed (1:84,700). We found a strikingly heterogeneous spectrum of 22 novel and eight reported mutations. Allelic variants were neither related to biochemical nor anamnestic data of our probands showing all asymptomatic or benign phenotypes. Comparative analysis of case reports with NBS data implied that only few individuals (< 10%) develop symptoms. In addition, none of the symptoms reported so far can clearly be attributed to MCCD. MCCD is a genetic condition with low clinical expressivity and penetrance. It largely represents as nondisease. So far, there are no genetic or biochemical markers that would identify the few individuals potentially at risk for harmful clinical expression. The low ratio of benefit to harm was pivotal to the decision to exclude MCCD from NBS in Germany. MCCD may be regarded as exemplary of the ongoing controversy arising from the inclusion of potentially asymptomatic conditions, which generates a psychological burden for afflicted families and a financial burden for health care systems.

Homocysteine is not associated with arterial thickness and stiffness in healthy middle-aged French volunteers

BACKGROUND

To study the association between the total plasma homocysteine (tHcy) concentration and the carotid artery intima-medial wall thickness (IMT), pulse wave velocity (PWV) and the presence of arterial plaques in a French population.

METHODS

Cross-sectional analysis of data from 556 male and 559 female middle-aged participants (mean (+/-SD) age 59.6+/-4.7 years) provided by an ongoing intervention trial.

RESULTS

Mean geometric tHcy concentration was higher for men than for women (10.6 vs. 8.5 micromol/L, p<0.001) and was associated in the expected direction with known determinants. The mean IMT was 0.71+/-0.1 mm for men and 0.69+/-0.1 mm for women (p<0.001), the mean PWV was, respectively, 12.0+/-2.8 and 10.9+/-2.2 m/sec (p<0.001), and the percentages of subjects with plaques were, respectively, 40.8% and 22.7% (p<0.001). In men only, the age-adjusted mean IMT and PWV increased with an increasing tHcy concentration: the IMT was 0.71 mm in the first tHcy-quartile and 0.73 mm in the fourth tHcy-quartile (p for linear trend=0.03), the PWV values were, respectively, 11.6 and 12.4 m/sec (p for linear trend=0.01). These associations disappeared after adjustment for conventional cardiovascular disease risk factors.

CONCLUSION

In this population, the tHcy concentration was not associated with measures of arterial thickness and stiffness.

Severe hypoglycaemia in isolated 3-methylcrotonyl-CoA carboxylase deficiency; a rare, severe clinical presentation

Since the introduction of neonatal screening for branched-chain organic acidurias, it has been noted that isolated 3-methylcrotonyl-CoA carboxylase deficiency is probably one of the most frequent organic acidurias. Only a few cases with severe clinical presentation have been described. Profound hypoglycaemia is an uncommon but life-threatening complication.

A common mutation is associated with a mild, potentially asymptomatic phenotype in patients with isovaleric acidemia diagnosed by newborn screening

Isovaleric acidemia (IVA) is an inborn error of leucine metabolism that can cause significant morbidity and mortality. Since the implementation, in many states and countries, of newborn screening (NBS) by tandem mass spectrometry, IVA can now be diagnosed presymptomatically. Molecular genetic analysis of the IVD gene for 19 subjects whose condition was detected through NBS led to the identification of one recurring mutation, 932C-->T (A282V), in 47% of mutant alleles. Surprisingly, family studies identified six healthy older siblings with identical genotype and biochemical evidence of IVA. Our findings indicate the frequent occurrence of a novel mild and potentially asymptomatic phenotype of IVA. This has significant consequences for patient management and counseling.

Isolated 3-methylcrotonyl-CoA carboxylase deficiency: evidence for an allele-specific dominant negative effect and responsiveness to biotin therapy

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.

A primer on expanded newborn screening by tandem mass spectrometry

Newborn screening (NBS) for a wide variety of inborn errors of metabolism using the powerful tool of tandem mass spectrometry (MS/MS) is becoming widespread. This article provides the basic information that primary care clinicians need to help make rational decisions about urgent evaluation and appropriate follow-up of patients with abnormal expanded NBS tests. Also outlined are ways that the screening tests can be inaccurate. A normal MS/MS NBS result does not rule out the possibility of an inborn error of metabolism in an infant with acute illness, developmental abnormalities,or other clinically suggestive conditions. Primary care practitioners should identify the metabolic specialists in their area and develop a relationship with them to ensure clear communication when abnormal results arrive. Included in this article is a catalog of "thumbnail sketches" for reference by physicians when they receive an abnormal MS/MS NBS result.