High Incidence of Partial Biotinidase Deficiency in the First 3 Years of a Regional Newborn Screening Program in Italy

Abstract

Biotinidase deficiency (BD) is an autosomal recessive inherited disorder in which the enzyme biotinidase is totally or partially defective and the vitamin biotin is not recycled. BD meets the major criteria for a population screening program. Newborn bloodspot screening (NBS) allows early diagnosis of BD, thus preventing the high morbidity and mortality associated with untreated disease. Both profound and partial BD variant can be detected by NBS test, and serum enzyme activity and/or mutational analysis are required for definitive diagnosis. In Italy, BD is included in the screening panel for inborn errors of metabolism (IEMs) that has been declared mandatory in 2016. We analyzed the data of the first 3 years of the NBS for BD in our region (Abruzzo, Italy), with the aim to describe the outcomes of this recently introduced screening program. In over 26,393 newborns screened, we found 2 carriers and 16 cases with genotype associated with partial BD. Since the serum biotinidase assay has been recently introduced in our algorithm, only three of our newborns met the criteria of genetic and biochemical confirmation, with an incidence of 1:8797, which is in the high range of what has been reported in the literature. All affected infants carried the 1330G>C (D444H) variant in compound heterozygosis, with variants known to be associated with profound BD. A variant previously not described and likely pathogenic was found in one newborn. None of the infants had signs or symptoms. The study of the distribution of the enzyme activity in our population allowed us to validate the adopted cutoff with which the program has a positive predictive value of 18% and to analyze some preanalytical factors influencing biotinidase activity: A correlation of the enzyme activity with gestational age and time at specimen collection was found. Lower mean values of enzyme activity were found in infants born in the summer.

Keywords: biotinidase activity; biotinidase deficiency; biotinidase gene variants; expanded newborn screening; inborn errors of metabolism; newborn blood spot screening.

Figure 1

DBS biotinidase activity distribution in all the newborns screened. The dotted line represents the 85 U/dL cutoff.

Figure 2

DBS biotinidase activity in false positives (gray boxes) and true positives (white boxes) at the initial and repeat DBS screening test.

Figure 3

Biotinidase activity at the DBS screening test and variants in carriers and in affected infants.

Figure 4

DBS biotinidase activity in relation to the birth weight (A) and to the pregnancy term (B).

Figure 5

Mean DBS biotinidase activity in relation to the birth season.

Figure 6

Mean biotinidase activity in DBS vs. the age at specimen collection.