Inspired by a patient identified on newborn screening
Abstract
3-methylcrotonyl-CoA carboxylase deficiency (3MCCD) is a hereditary disorder of leucine catabolism caused by pathogenetic variants in the MCCC1 or MCCC2 genes. Typically diagnosed through newborn screening (NBS), 3MCCD is characterized by elevation of 3-hydroxyisovalerylcarnitine (C5OH) in blood as well as increased excretion of 3-methylcrotonylglycine (3-MCG) in urine. While most diagnosed children remain asymptomatic, data on adults are scarce. To date, only 39 molecularly confirmed adult individuals have been reported, all being mothers diagnosed subsequent to their child NBS results. Herein, we present a 36-year-old asymptomatic man who was incidentally diagnosed with 3MCCD following his son NBS recall. Molecular analysis revealed compound heterozygosity for two pathogenic variants in the MCCC1 gene. This is the first molecularly confirmed adult man with 3MCCD reported. This case highlights the need for additional longitudinal follow-up data on individuals with 3MCCD to clarify the clinical significance of this condition and guide clinical practice, including NBS strategy.
Lin W, Wang K, Chen Y, Zheng Z, Lin Y. Newborn screening and genetic diagnosis of 3-methylcrotonyl-CoA carboxylase deficiency in Quanzhou,China. Mol Genet Metab Rep. 2024 Aug 2;40:101127. doi: 10.1016/j.ymgmr.2024.101127. PMID: 39188588; PMCID: PMC11345313.
Abstract
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.
Jagadish A, Sclater K, Lapinski T, Adkins K, Selzer L. A Unique Presentation of 3-Methylcrotonyl-CoA Carboxylase Deficiency. Cureus. 2023 May 23;15(5):e39401. doi: 10.7759/cureus.39401. PMID: 37362523; PMCID: PMC10287026.
Abstract
3-methylcrotonyl-CoA carboxylase deficiency is an autosomal recessive disorder resulting in impaired leucine metabolism. The condition is typically diagnosed with newborn screening; patients diagnosed at a later stage generally present with symptoms including metabolic disturbances, seizures, failure to thrive, or delayed development. We present the case of a child diagnosed at 12 months of age who was noted to have recurrent viral infections and nonspecific gastrointestinal symptoms of vomiting, hematochezia, and gaseous distention of the abdomen. Newborn screening did not reveal any abnormalities. Evaluation for underlying immunodeficiency was unremarkable; genetic testing revealed bi-allelic mutations in MCCC2, a known association of 3-methylcrotonyl-CoA carboxylase deficiency. It is important to consider genetic disorders when evaluating patients even if the newborn screening is unremarkable.
Wang H, Liu S, Wang B, Yang Y, Yu B, Wang L, Wang T. 3-Methylcrotonyl-CoA carboxylase deficiency newborn screening in a population of 536,008: is routine screening necessary? J Pediatr Endocrinol Metab. 2019 Dec 18;32(12):1321-1326. doi: 10.1515/jpem-2018-0536. PMID: 31730530.
Abstract
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.
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