Article Detection of a monoclonal component after pediatric liver transplantation: a case report was published on August 15, 2022 in the journal Clinical Chemistry and Laboratory Medicine (CCLM) (volume 0, issue 0).

Acetoacetyl-CoA thiolase deficiency, also known as Beta-ketothiolase deficiency (BKTD), is an autosomal recessive organic aciduria included in the Italian newborn screening (NBS) panel. It is caused by mutations in the ACAT1 gene, which encodes the mitochondrial acetyl-CoA acetyltransferase. Its deficiency impairs the degradation of isoleucine and acetoacetyl-CoA, leading to the accumulation of toxic metabolites. We describe three cases of BKTD. The first newborn showed increase in C5:1, C4DC/C5OH, C3DC/C4OH in the NBS. Urinary organic acids (uOAs) revealed marked excretion of 2-methyl-3-hydroxybutyrate. Tiglylglycine was absent. Genetic testing identified the compound heterozygosity for two pathogenic ACAT1 variants. The second patient showed increased levels of C5:1, C4DC/C5OH, C3DC/C4OH in the NBS. uOAs revealed 2-methyl-3-hydroxybutyrate and tiglylglycine. A homozygous VUS in ACAT1 was identified. The third case showed elevation of C4DC/C5OH, C3DC/C4OH in the NBS, with a slight increase in C5:1. uOAs showed 2-methyl-3-hydroxybutyrate and tiglylglycine. A homozygous missense VUS was identified in the ACAT1 gene. BKTD exhibited variable NBS biochemical phenotypes across the three cases. While C5OH and C5:1, the primary markers, were not consistently elevated in all our cases, C4OH strongly increased in all three. Our findings support the use of C4OH in a combined marker strategy to improve BKTD NBS.

Metachromatic leukodystrophy (MLD) is a rare, autosomal recessive lysosomal storage disorder caused by a deficiency of the enzyme arylsulfatase A (ARSA, MIM #250100), which leads to progressive demyelination in the central and peripheral nervous systems, resulting in severe neurodegeneration and premature death. With the recent approval of the first ex vivo gene therapy for MLD, newborn screening (NBS) programs have begun to implement pilot studies for early detection, as identifying affected individuals during the pre-symptomatic therapeutic window is crucial. We present the analytical workflow and the NBS algorithm developed during the first year of MLD screening in Lombardy. The screening strategy comprised a first-tier test (1TT) using mass spectrometry to quantify sulfatide concentrations, a second-tier test (2TT) measuring ARSA enzymatic activity, and a third-tier test (3TT) based on whole-exome sequencing. A total of 16,130 newborns were screened for MLD. Of these, 6.41% required retesting (1TT), 1.53% underwent duplicate 2TT, and 0.36% proceeded to 3TT. No neonates were recalled, and no cases of MLD were identified through the screening program. The first-year implementation of MLD NBS in Lombardy demonstrates that a mass spectrometry-based sulfatide assay combined with a multi-tiered screening algorithm is feasible and reliable. Incorporating genetic analysis alongside expanded validation of additional sulfatide species may enhance specificity, reduce false positives, and facilitate timely identification of infants affected by MLD.