Newborn Screening Alone Cannot Prevent Most Cases of Severe Vitamin B12 Deficiency in the First Year of Life.

Background/objectives Vitamin B12 (B12) is essential for the provision of methyl groups for numerous essential pathways. Infant B12 deficiency (B12D) can lead to severe, even irreversible neurological abnormalities. Maternal B12 status in pregnancy and during the breastfeeding period correlates significantly with the child's B12 status. B12D is a target disease in some newborn screening (NBS) programs. This study investigates whether infants that were clinically symptomatic and diagnosed with B12D in their first year of life could be retrospectively detected by the Austrian NBS algorithm.Methods Data from infants with clinically diagnosed B12D in their first year of life between 2012 and 2022 were retrospectively collected in Austria (B12-related NBS implemented in 2018) and Switzerland (B12-related NBS not implemented). NBS data were retrospectively analysed, and clinical information was collected by a survey. Correlations between clinical symptoms, NBS data, biochemical parameters at diagnosis, maternal medical history and B12 status were analysed.Results Four/forty-eight cases were retrospectively detected by the first-tier NBS parameters. From two children material for second-tier testing was available and B12D was confirmed by elevated total homocysteine (tHcy), resulting in a detection rate between 4.3 and 9.3%. The numbers of neurological and haematological symptoms correlated with low B12 and elevated levels of tHcy and methylmalonic acid. Although the detection rate of symptomatic B12D by NBS was low, fewer infants with symptomatic B12D were observed in the period after implementation of B12-related NBS (Austria). A history of B12D-relevant maternal disease such as pernicious anaemia was reported in 12 cases.Conclusions B12D causes severe clinical symptoms in infants. NBS has a very limited retrospective detection rate of infants with severe B12D but seems to correlate with a reduction in cases due to not yet precisely quantified mechanisms. The workup triggered by NBS recalls is costly and often challenging for families. Maternal B12D increases the risk of infant B12D but also of other pregnancy-related health risks. To increase the efficacy of the prevention of infant B12D, to promote a healthy pregnancy and breastfeeding period, and to reduce the frequency of NBS recalls, pregnant women should be screened for B12D to be counselled and treated.