Tandem Mass Spectrometry for the Analysis of Plasma/Serum Acylcarnitines for the Diagnosis of Certain Organic Acidurias and Fatty Acid Oxidation Disorders

Acylcarnitines are formed in the mitochondria by esterification between carnitine and acyl-CoAs. This occurs enzymatically via carnitine acyltransferases. Specific acylcarnitines accumulate as a result of various organic acidurias and fatty acid oxidation disorders, and, thus, acylcarnitines profiles are used for the diagnosis of these disorders. Acylcarnitines monitoring can also be used for the follow-up of patients with these disorders. Tandem mass spectrometry (MS/MS) is the most commonly used method for the analysis of acylcarnitines. An MS/MS method for the quantification of a number of acylcarnitines is described. The method involves butylation of acylcarnitines using acidified butanol. Butylated acylcarnitines are analyzed using flow injection and precursor ion scan. Multiple-reaction monitoring (MRM) is used for the analysis of low-molecular-weight acylcarnitines.

Delayed diagnosis of holocarboxylase synthetase deficiency in three patients with prominent skin findings

Holocarboxylase deficiency (HLCSD) is caused by biallelic pathogenic variants in HLCS and is associated with poor feeding, emesis, lethargy, seizures, life-threatening metabolic acidosis, and hyperammonemia. Skin involvement in HLCSD is typically described as scaly, erythrodermic, seborrhea-like, or ichthyosiform, but there is a paucity of reports. We report three patients, including two siblings, with HLCSD and significant cutaneous manifestations including ichthyosiform dermatitis and a presentation with features of annular pustular psoriasis. In this report, we show that persistent, unexplained rash, even in the absence of other clinical findings, should warrant consideration and potential workup for HLCSD.

Biochemical signatures mimicking multiple carboxylase deficiency in children with mutations in MT-ATP6

Elevations of specific acylcarnitines in blood reflect carboxylase deficiencies, and have utility in newborn screening for life-threatening organic acidemias and other inherited metabolic diseases. In this report, we describe a newly-identified association of biochemical features of multiple carboxylase deficiency in individuals harboring mitochondrial DNA (mtDNA) mutations in MT-ATP6 and in whom organic acidemias and multiple carboxylase deficiencies were excluded. Using retrospective chart review, we identified eleven individuals with abnormally elevated propionylcarnitine (C3) or hydroxyisovalerylcarnitine (C5OH) with mutations in MT-ATP6, most commonly m.8993T>G in high heteroplasmy or homoplasmy. Most patients were ascertained on newborn screening; most had normal enzymatic or molecular genetic testing to exclude biotinidase and holocarboxylase synthetase deficiencies. MT-ATP6 is associated with some cases of Leigh disease; clinical outcomes in our cohort ranged from death from neurodegenerative disease in early childhood to clinically and developmentally normal after several years of follow-up. These cases expand the biochemical phenotype associated with MT-ATP6 mutations, especially m.8993T>G, to include acylcarnitine abnormalities mimicking carboxylase deficiency states. Clinicians should be aware of this association and its implications for newborn screening, and consider mtDNA sequencing in patients exhibiting similar acylcarnitine abnormalities that are biotin-unresponsive and in whom other enzymatic deficiencies have been excluded.