Profound biotinidase deficiency: a rare disease among native Swedes.
Biotinidase deficiency is an autosomal recessive metabolic disorder included in many newborn screening programmes. Prior to the introduction of screening for biotinidase deficiency in Sweden in 2002, the disorder was almost unknown, with only one case diagnosed clinically. Biotinidase activity was measured in dried blood spots with a semiquantitative method using biotin-6-amidoquinoline as substrate. The cutoff value was set at 25% (later lowered to 20%) of the mean activity of all samples measured on that day. The disorder was confirmed by quantitative determination of biotinidase activity in plasma and DNA analyses. Over a period of 6 years, 13 patients were identified among 637,452 screened newborns and 5,068 adoptive/immigrant children. None of the patients had clinical symptoms at the time of diagnosis. Six patients had profound biotinidase deficiency, with an activity of 0-5% of normal in plasma. Four of these patients were born to parents who were first cousins of Middle Eastern or African origin. Eighteen gene alterations were identified, nine of which have not previously been described: seven mutations p.L83S (c.248T > C), p.R148H (c.443G > A), p.N202I (c.605A > T), p.I255T (c.764T > C), p.N402S (c.1205A > G), p.L405P (c.1214T > C), p.G445R (c.1333G > A) and two silent mutations p.L71L (c.211C > T) and p.L215L (c.645C > T). The predicted severity of the novel mutations was analyzed by sorting intolerant from tolerant (SIFT) and polymorphism phenotyping (PolyPhen), predicting p.L83S, p.L405P and p.G445R as severe mutations. Due to the high rate of immigrants since 1990 from non-Nordic countries, the incidence of biotinidase deficiency is similar to that found in many other Western countries.
Division of Metabolic Diseases, Department of Laboratory Medicine, Karolinska Institute, Karolinska University Hospital, Stockholm SE-141 86, Sweden. annika.ohlsson@ki.se
Annika
A
Ohlsson
Claes
C
Guthenberg
Elisabeth
E
Holme
Ulrika
U
von Döbeln
D000328:Adult; D000634:Aminoquinolines / Q000378:metabolism; D015415:Biomarkers / Q000097:blood; D001710:Biotin / Q000031:analogs & derivatives / Q000378:metabolism / Q000627:therapeutic use; D043523:Biotinidase / Q000097:blood / Q000235:genetics*; D028921:Biotinidase Deficiency / Q000175:diagnosis / Q000188:drug therapy / Q000201:enzymology / Q000453:epidemiology* / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D004252:DNA Mutational Analysis; D019587:Dietary Supplements; D059788:Dried Blood Spot Testing; D054242:Emigrants and Immigrants; D020022:Genetic Predisposition to Disease; D005820:Genetic Testing; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D009154:Mutation; D015997:Neonatal Screening / Q000379:methods; D010375:Pedigree; D010641:Phenotype; D011110:Polymorphism, Genetic; D012720:Severity of Illness Index; D013379:Substrate Specificity; D013548:Sweden / Q000453:epidemiology; D013997:Time Factors; D016896:Treatment Outcome
D000634:Aminoquinolines; D015415:Biomarkers; D001710:Biotin; D043523:Biotinidase