Biochemical Comparation Between Infants with Deficiency of Vitamin B12 Secondary to Maternal Deficiency and due to Genetic Disorder

Background: Vitamin B12 or Cobalamin (Cbl) plays an important role in many metabolic pathways. Its deficiency can lead to a wide spectrum of hematologic and neurological disorders that can be reversed or minimized by early diagnosis and prompt treatment. Cbl deficiency in newborns/infants may be secondary to nutritional deficits or due to defects in the absorption, transport or intracellular metabolism of Cbl, and can be identified in Portuguese newborn screening by analysis of acylcarnitine profile.

Objective: Compare biochemical parameters of infants with deficiency of Cbl secondary to maternal deficiency to infants with genetic deficit.

Methods: Included infants referred due to suspicion of Cbl deficit, between 2009 and 2018. Data from neonatal metabolic screening and infants and mothers clinical files.

Results: Were identified 8 breastfed infants, 4 with deficiency secondary to maternal cause and 4 with CblC disorder (an inborn error of the intracellular metabolism of Cbl, secondary to mutations in MMACHC gene). Seven were referred in the first month of life, due to alterations in neonatal screening, and one was diagnosed at 5 months of age when evaluated by growth and development impairment.

In newborn screening, the mean levels of propyonilcarnitine and propyonilcarnitine/acetylcarnitine ratio was two times higher in infants with genetic disorder. In these patients the serum Cbl was higher (10 times), as well as, the levels of methylmalonic acid (3.5 times) and homocysteine (4 times). Contrariwise, the mean levels of methionine were 1.6 times higher in nutritional deficit.

Conclusion: The mean values ​​of the acylcarnitines, methylmalonic acid, and homocysteine are higher in the genetic CblC deficiency, when compared to nutritional deficits. However, the size of this sample does not allow conclusions regarding of cutoffs for each parameter.