Outcomes of individuals with profound and partial biotinidase deficiency ascertained by newborn screening in Michigan over 25 years

PurposeBiotinidase deficiency, if untreated, usually results in neurological and cutaneous symptoms. Biotin supplementation markedly improves and likely prevents symptoms in those treated early. All states in the United States and many countries perform newborn screening for biotinidase deficiency. However, there are few studies about the outcomes of the individuals identified by newborn screening.MethodsWe report the outcomes of 142 children with biotinidase deficiency identified by newborn screening in Michigan over a 25-year period and followed in our clinic; 22 had profound deficiency and 120 had partial deficiency.ResultsIndividuals with profound biotinidase and partial deficiency identified by newborn screening were started on biotin therapy soon after birth. With good compliance, these children appeared to have normal physical and cognitive development. Although some children exhibited mild clinical problems, these are unlikely attributable to the disorder. Biotin therapy appears to prevent the development of neurological and cutaneous problems in our population.ConclusionIndividuals with biotinidase deficiency ascertained by newborn screening and treated since birth appeared to exhibit normal physical and cognitive development. If an individual does develop symptoms, after compliance and dosage issues are excluded, then other causes must be considered.     

The neurology of biotinidase deficiency

Biotinidase deficiency is an autosomal recessively inherited metabolic disorder in which the enzyme, biotinidase, is defective and the vitamin, biotin, is not recycled. Individuals with biotinidase deficiency, if not treated with biotin, usually exhibit neurological and cutaneous abnormalities. Biotin treatment can ameliorate or prevent symptoms. Biotinidase deficiency meets the major criteria for inclusion in newborn screening programs. With the advent of universal newborn screening for the disorder, the "window-of-opportunity" to characterize the consequences of the untreated disease is essentially gone. To understand the neurology of biotinidase deficiency, we must depend on what is already known about symptomatic individuals with the disorder. Therefore, in this review, the neurological findings of symptomatic individuals with profound biotinidase deficiency have been compiled to catalog the characteristic features of the disorder and the consequences of biotin treatment on these findings. In addition, based on the available evidence, I have speculated on the cause of neurological problems associated with the disorder. Future studies in biotinidase-deficient animals should allow us to demonstrate more definitively if these speculations are correct.     

Profound biotinidase deficiency in two asymptomatic adults

Biotinidase deficiency is an autosomal-recessive disorder of biotin recycling. Children with profound biotinidase deficiency usually have neurological and cutaneous symptoms in early childhood, but they may not develop symptoms until adolescence. We now report on a man and a woman with profound biotinidase deficiency who are asymptomatic and who were diagnosed only because their biotinidase-deficient children were identified by newborn screening. These adults have never exhibited symptoms of the disorder and are homozygous for two different mutations resulting in different aberrant enzymes. There is no evidence of an increased dietary intake of biotin to explain why they have remained asymptomatic. Although these adults may still be at risk for developing symptoms, they could represent a small group of individuals with profound biotinidase deficiency who will never develop clinical problems. Their lack of symptoms suggests that there are probably epigenetic factors that protect some enzyme-deficient individuals from developing symptoms. These individuals broaden the spectrum of expression of biotinidase deficiency. Am. J. Med. Genet. 73:5–9, 1997. © 1997 Wiley-Liss, Inc.     

Real time PCR assays to detect common mutations in the biotinidase gene and application of mutational analysis to newborn screening for biotinidase deficiency

Biotinidase deficiency is an autosomal recessive disorder of biotin metabolism caused by defects in the biotinidase gene. Symptoms of biotinidase deficiency are resolved or prevented with oral biotin supplementation and as such newborn screening is performed to prospectively identify affected individuals prior to the onset of symptoms. Biotinidase deficiency is detected by determining the activity of the biotinidase enzyme utilizing the newborn dried blood spot and colorimetric end point analysis. While newborn screening by enzyme analysis is effective, external factors may compromise results of the enzyme analysis and difficulty is encountered in distinguishing between complete and partial enzyme deficiencies. In the United States, the four mutations most commonly associated with complete biotinidase deficiency are c98:d7i3, Q456H, R538C, and the double mutation D444H:A171T. Partial biotinidase deficiency is almost universally attributed to the D444H mutation. To more effectively distinguish between profound and partial biotinidase deficiency, a panel of assays utilizing real time PCR and melting curve analysis using Light Cycler technology was developed. Employing DNA extracted from the original dried blood specimens from newborns identified through prospective newborn screening as presumptive positive for biotinidase deficiency, the specimens were analyzed for the presence of the five common mutations. Using this approach it was possible to separate newborns with partial and complete deficiency from each other as well as from many of those with false positive results. In most cases it was also possible to correlate the genotype with the degree of residual enzyme activity present. In newborn screening for biotinidase deficiency, we have shown that the analysis of common mutations is useful in distinguishing between partial and complete enzyme deficiency as well as improving specificity. Combining biotinidase enzyme analysis with genotypic data also increases the sensitivity of screening for biotinidase deficiency and provides information useful to clinicians earlier than would otherwise be possible.     

Analysis of mutations causing biotinidase deficiencya

Biotinidase deficiency is an inherited disorder in which the vitamin, biotin, is not recycled. Individuals with biotinidase deficiency can develop neurological and cutaneous symptoms if they are not treated with biotin. Biotinidase deficiency screening has been incorporated into essentially all newborn screening programs in the United States and in many countries. We now report 140 known mutations in the biotinidase gene (BTD) that cause biotinidase deficiency. All types of mutations have been found to cause biotinidase deficiency. Variants have been identified throughout the coding sequence. Essentially all the variants result in enzymatic activities with less than 10% of mean normal enzyme activity (profound biotinidase deficiency) with the exception of the c.1330G>C (p.D444H) mutation, which results in an enzyme having 50% of mean normal serum activity. The putative three‐dimensional structure of biotinidase has been predicted by homology to that of nitrilases/amidases. The effect of the various missense mutations can be predicted to affect various important sites within the structure of the enzyme. This compilation of variants causing biotinidase deficiency will be useful to clinical laboratories that are performing mutation analysis for confirmational testing when the enzymatic results are equivocal for children identified through newborn screening. Hum Mutat 31:983–991, 2010. © 2010 Wiley‐Liss, Inc.     

Development and characterization of a mouse with profound biotinidase deficiency: a biotin-responsive neurocutaneous disorder

Biotinidase deficiency is the primary enzymatic defect in biotin-responsive, late-onset multiple carboxylase deficiency. Untreated children with profound biotinidase deficiency usually exhibit neurological symptoms including lethargy, hypotonia, seizures, developmental delay, sensorineural hearing loss and optic atrophy; and cutaneous symptoms including skin rash, conjunctivitis and alopecia. Although the clinical features of the disorder markedly improve or are prevented with biotin supplementation, some symptoms, once they occur, such as developmental delay, hearing loss and optic atrophy, are usually irreversible. To prevent development of symptoms, the disorder is screened for in the newborn period in essentially all states and in many countries. In order to better understand many aspects of the pathophysiology of the disorder, we have developed a transgenic biotinidase-deficient mouse. The mouse has a null mutation that results in no detectable serum biotinidase activity or cross-reacting material to antibody prepared against biotinidase. When fed a biotin-deficient diet these mice develop neurological and cutaneous symptoms, carboxylase deficiency, mild hyperammonemia, and exhibit increased urinary excretion of 3-hydroxyisovaleric acid and biotin and biotin metabolites. The clinical features are reversed with biotin supplementation. This biotinidase-deficient animal can be used to study systematically many aspects of the disorder and the role of biotinidase, biotin and biocytin in normal and in enzyme-deficient states.     

Double mutation (A171T) and (D444H) is a common cause of profound biotinidase deficiency in children ascertained by newborn screening in the United States

Biotinidase deficiency is inherited as an autosomal recessive trait that, unless treated with pharmacologic doses of biotin, can result in neurologic and cutaneous symptoms. We have identified two new mutations in exon D of the biotinidase gene of children with profound biotinidase deficiency ascertained by newborn screening. Transition 511G→A near the 5′ end of exon D results in a substitution of threonine for alanine171 (A171T) and transversion 1330G→C occurs close to the 3′ end of exon D causing a substitution of histidine for aspartic acid 444 (D444H). The D444H mutation was detected in four individuals from our normal population whose mean serum biotinidase activity is 5.25 nmol/min/ml, which is significantly lower than the mean normal activity (7.1 nmol/min/ml). We calculated that this mutation causes a 52% loss of activity in the aberrant enzyme. Twenty-three individuals with the D444H mutation were found by allele specific oligonucleotide analysis of DNA from 296 randomly-selected, anonymous dried-blood spots. We estimate the frequency of this allele in the general population to be 0.039. In contrast, no individuals in 376 have the A171T mutation. Fourteen children (eleven probands and three siblings) out of 31 enzyme-deficient children have both the A171T and D444H mutations. Both mutations are inherited from a single parent as a double mutation allele. The nine families in which this allele was identified are of mostly European ancestry, although the mutation cannot be attributed to a specific nationality or ethnic group. The serum of a child who is homozygous for the double mutation allele has very little CRM and the aberrant enzyme has very low biotinyl-hydrolase activity and no biotinyl-transferase activity. This double mutation allele (A171T and D444H) is a common cause of profound biotinidase deficiency in children ascertained by newborn screening in the United States. Hum Mutat 11:410, 1998. © 1998 Wiley-Liss, Inc.     

Double mutation (A171T and D444H) is a common cause of profound biotinidase deficiency in children ascertained by newborn screening the the United States. Mutations in brief no. 128. Online

Biotinidase deficiency is inherited as an antosomal recessive trait that, unless treated with pharmacologic doses of biotin, can result in neurologic and cutaneous symptoms. We have identified two new mutations in exon D of the biotinidase gene of children with profound biotinidase deficiency ascertained by newborn screening. Transition 511G->A near the 5' end of exon D results in a substitution of threonine for alanine 171 (A171T) and transversion 1330G->C occurs close to the 3' end of exon D causing a substitution of histidine for aspartic acid 444 (D444H). The D444H mutation was detected in four individuals from our normal population whose mean serum biotinidase activity is 5.25 nmol/min/ml, which is significantly lower than the mean normal activity (7.1 nmol/min/ml). We calculated that this mutation causes a 52% loss of activity in the aberrant enzyme. Twenty-three individuals with the D444H mutation were found by allele specific oligonucleotide analysis of DNA from 296 randomly-selected, anonymous dried-blood spots. We estimate the frequency of this allele in the general population to be 0.039. In contrast, no individuals in 376 have the A171T mutation. Fourteen children (eleven probands and three siblings) out of the 31 enzyme-deficient children have both the A171T and D444H mutations. Both mutations are inherited from a single parent as a double mutation allele. The nine families in which this allele was identified are of mostly European ancestry, although the mutation cannot be attributed to a specific nationality or ethnic group. The serum of a child who is homozygous for the double mutation allele has very little CRM and the aberrant enzyme has very low biotinylhydrolase activity and no botinyl-transferase activity. This double mutation allele (A171T and D444H) is a common cause of profound biotinidase deficience in children ascertained by newborn screening in the United States.     

Biotinidase deficiency: "if you have to have an inherited metabolic disease, this is the one to have"

Biotinidase recycles the vitamin biotin. Biotinidase deficiency is an autosomal recessively inherited neurocutaneous disorder. The symptoms of the disorder can be successfully treated or prevented by administering pharmacological doses of biotin. The biotinidase gene (BTD) has been cloned and sequenced; its genomic organization has been determined and more than 150 mutations have been identified. The disorder meets the major criteria for newborn screening and is being universally adopted in the United States and in many countries around the world. Newborn screening will limit our understanding about the natural history of the disorder. Regardless, the disorder is an ideal example of an inherited metabolic disorder that if untreated can result in major disabilities, but if identified early can be readily treated by the oral administration of a vitamin.     

Technical standards and guidelines for the diagnosis of biotinidase deficiency

Biotinidase deficiency is an autosomal recessively inherited disorder of biotin recycling that is associated with neurologic and cutaneous consequences if untreated. Fortunately, the clinical features of the disorder can be ameliorated or prevented by administering pharmacological doses of the vitamin biotin. Newborn screening and confirmatory diagnosis of biotinidase deficiency encompasses both enzymatic and molecular testing approaches. These guidelines were developed to define and standardize laboratory procedures for enzymatic biotinidase testing, to delineate situations for which follow-up molecular testing is warranted, and to characterize variables that can influence test performance and interpretation of results.     

Increased incidence of profound biotinidase deficiency among Hispanic newborns in California

We report population findings from newborn screening for biotinidase deficiency in California, representing over 2,000,000 newborns. The incidence of profound deficiency was 1/73,629, higher than in other reported populations. Out of 28 patients with profound biotinidase deficiency, 19 were of Hispanic descent, suggesting an increased frequency among this group. Of the 28 patients, 23 underwent mutation analysis of the BTD gene, with one common mutation, 528G>T, found in 43.3% of Hispanic alleles tested.     

Clinical findings in four children with biotinidase deficiency detected through a statewide neonatal screening program

Four children with biotinidase deficiency were identified during the first year of a neonatal screening program for this disease in the Commonwealth of Virginia. Two unrelated probands were identified among the 81,243 newborn infants who were screened. In addition, two siblings of one of these infants were found to be affected. Both probands had mild neurologic symptoms at two and four months, respectively, and the two older children had more severe neurologic abnormalities, cutaneous findings, and developmental delay at two and three years of age. However, none of the affected children had acute metabolic decompensation. Previous studies have shown that the administration of biotin to affected children can be a lifesaving procedure that can reverse acute symptoms and prevent irreversible neurologic damage. Our findings demonstrate that subtle neurologic abnormalities may appear as early as at two months of age and that developmental abnormalities may occur even in the absence of episodes of overt metabolic decompensation. Since screening and treatment are both inexpensive and effective and the incidence of the disease is well within the range of that of other metabolic diseases for which screening is performed, biotinidase deficiency should be added to the group of metabolic diseases for which screening is done in the neonatal period.     

Mutational analysis for biotinidase deficiency of a Greek patients' cohort ascertained through expanded newborn screening

Late-onset multiple carboxylase deficiency, also known as biotinidase (BTD) deficiency, is an autosomal recessively inherited disorder of biotin metabolism. Its early diagnosis and treatment seems that it can even fully prevent its various clinical manifestations. Mutations in the BTD gene scattered throughout its coding region have been detected in patients ascertained either through newborn screening or clinically. From March 2010 up to June 2011, 18?954 Greek neonates were subjected to biochemical determination of BTD activity through a semiquantitative fluoroimmunoassay. Subsequently, the first cohort of our 'suspected' samples was further tested for the presence of aberrations associated either with partial or profound BTD deficiency through sequencing of the coding region of the BTD gene, including splice-site junctions. On the basis of the molecular data derived from the study of our first cohort of 'suspected' samples, a panel of four mutations, most frequently encountered in the Greek population, was created, and a rapid, reliable and cost-effective real-time-based genotyping assay for the detection of these mutations was developed. This is the first report about the BTD mutational spectrum in Greece, and it could be a beneficial utility in the differential clinical diagnosis of BTD deficiency.     

Novel mutations causing biotinidase deficiency in individuals identified by the newborn screening program in Minas Gerais,Brazil

Biotinidase deficiency is an autosomal recessive inherited metabolic disorder caused by mutations in the BTD gene. Clinical manifestations can be treated and effectively prevented with pharmacological doses of biotin. Nine novel mutations in BTD are reported in 14 children diagnosed by the newborn screening program in Minas Gerais, Brazil, from June 2013 to December 2017. Serum BTD enzyme activity was determined for all cases and some parents. Two of the mutations are deletions and seven missense mutations located in the exonic region of the BTD gene, mostly in exon 4. Two newborns were profoundly biotinidase‐deficient (one homozygous p.A534V [c.1601C > T] and another, double heterozygous for a novel mutation p.R211S [c.631C > A] co‐inherited with an already described mutation p.T532 M [c.1595C > T]). Two mutations were associated with a partial deficiency of biotinidase (p.F361 V [c.1081 T > G] in two homozygous children, and p.S311 T [c.932G > C] in a compound heterozygous child who co‐inherited a known severe mutation p.Y438X [c.1314 T > A]). The remaining five mutations were found in compound heterozygous children. Hence, a definitive conclusion about the degree of biotinidase deficiency is not possible yet. These results emphasize the importance of sequencing the BTD gene as an important tool to gain a better understanding of the correlation between biochemical phenotype and genotype.     

Morbidity and mortality among exclusively breastfed neonates with medium-chain acyl-CoA dehydrogenase deficiency

PurposeDespite greatly improved morbidity and mortality among infants with medium-chain acyl-CoA dehydrogenase deficiency (MCAD) since the implementation of universal newborn screening (NBS), a population of neonates still becomes ill before their positive screen results are available. Exclusive breastfeeding is a proposed risk factor in this group. Since initial studies of MCAD NBS, breastfeeding rates have increased substantially. In this study, we quantify the current risk of early decompensation in neonates with MCAD and identify factors associated with poor outcomes.MethodsWe completed a retrospective analysis of neonates with MCAD referred to our center between 2010 and 2015.ResultsOf 46 infants with MCAD, 11 (23.9%) were symptomatic before the return of the NBS results. Four died or had cardiac arrest; the remaining seven had lethargy and hypoglycemia. All symptomatic patients were exclusively breastfed; only 40.6% of asymptomatic patients were exclusively breastfed. Breastfeeding rates increased from 45.5% in 2010–2011 to 64.7% in 2012–2013 and 87.5% in 2014–2015. Over these same periods, rates of early decompensation increased from 9.09% to 23.5% and 75%, respectively.ConclusionsExclusively breastfed neonates with MCAD are at risk for early metabolic decompensation. As breastfeeding rates increase, close management of feeding difficulties is essential for all neonates awaiting NBS results.Genet Med 18 12, 1315–1319.     

Consanguinity and rare mutations outside of MCCC genes underlie nonspecific phenotypes of MCCD

Purpose3-Methylcrotonyl-CoA carboxylase deficiency (MCCD) is an autosomal recessive disorder of leucine catabolism that has a highly variable clinical phenotype, ranging from acute metabolic acidosis to nonspecific symptoms such as developmental delay, failure to thrive, hemiparesis, muscular hypotonia, and multiple sclerosis. Implementation of newborn screening for MCCD has resulted in broadening the range of phenotypic expression to include asymptomatic adults. The purpose of this study was to identify factors underlying the varying phenotypes of MCCD.MethodsWe performed exome sequencing on DNA from 33 cases and 108 healthy controls. We examined these data for associations between either MCC mutational status, genetic ancestry, or consanguinity and the absence or presence/specificity of clinical symptoms in MCCD cases.ResultsWe determined that individuals with nonspecific clinical phenotypes are highly inbred compared with cases that are asymptomatic and healthy controls. For 5 of these 10 individuals, we discovered a homozygous damaging mutation in a disease gene that is likely to underlie their nonspecific clinical phenotypes previously attributed to MCCD.ConclusionOur study shows that nonspecific phenotypes attributed to MCCD are associated with consanguinity and are likely not due to mutations in the MCC enzyme but result from rare homozygous mutations in other disease genes.Genet Med17 8, 660–667.     

Biotinidase deficiency: novel mutations and their biochemical and clinical correlates

Biotinidase deficiency is a defect in the recycling of the vitamin biotin. Biotin supplementation can markedly improve the neurological and cutaneous symptoms of affected children and prevent symptoms in children identified by newborn screening or treated since birth. We have determined thirteen novel mutations in children with the disorder. Two nonsense mutations, eight single missense mutations, three allelic double missense mutations, and two are polymorphisms were identified in the biotinidase gene (BTD). One of the missense mutations, c.734G>A (p. C245Y), is the first to be reported that alters the cysteine in the putative location crucial for ester formation and binding of the biotinyl-moiety in the active site of the enzyme. These mutations add to the growing list of mutations that are helping to delineate structure/function relationships of the enzyme.     

Health-care providers’ perspectives on uncertainty generated by variant forms of newborn screening targets

PurposeDespite the public health successes of newborn bloodspot screening, uncertainty associated with variant forms of primary screening targets has led to discrepancies in medical management. This study explored health-care providers’ approaches to managing atypical forms of inherited metabolic diseases (IMDs) in the absence of evidence-based guidelines.MethodsSemistructured telephone interviews were conducted with metabolic specialists. 3-Methylcrotonyl CoA deficiency and variant forms of phenylketonuria, biotinidase deficiency, and fatty acid oxidation disorders were considered. Data were analyzed inductively and deductively using a novel taxonomy of uncertainty.ResultsHealth-care providers (n = 12) navigate diagnostic, prognostic, and therapeutic challenges of uncertainty while interpreting patient and family attitudes, preferences, and ideas in the care of children with these result types. Participants explained the limits of classifying mild and atypical metabolic phenotypes. Participants also described the challenge of finding balance between cautious care and overmedicalization. Developing consistent care plans and honest communication with families were perceived as effective strategies when navigating uncertainty.ConclusionProviders’ experiences suggest a need for transparent and accessible guidelines that account for challenges associated with uncertainty generated by screening. Timely consideration of this challenge is warranted with increasing emergence of genotype-first approaches to screening.     

Three dimensional structure of human biotinidase: computer modeling and functional correlations

Untreated individuals with deficient activity of biotinidase, the enzyme responsible for recycling the vitamin biotin, usually exhibit neurological and cutaneous findings. To better understand the variability in expression of the disorder it is important to understand the structure of the enzyme and the putative effects of various mutations on its activity. Past attempts to express and purify sufficient quantities of the enzyme by us and others have failed. Therefore, we have resorted to computer modeling using homologous related, crystallized nitrilases/amidases to predict the 3-dimensional structure of biotinidase. The resultant structure is a two domain protein with the catalytic triad consisting of glutamate, lysine and cysteine, within the larger domain. The model predicts multiple glycosylation sites at the surface of the enzyme and multiple disulfide bonds. The precise location of the biotin-binding site could not be determined. Characteristics of 45 missense mutations known to cause profound and partial biotinidase deficiency were examined, including their location, their distance from the catalytic triad, and their potential effect on the structure of the enzyme. Although there are obviously short-comings in predicting the 3-dimensional structure of a protein without crystallographic data, because of the marked homology between biotinidase and specific crystallized amidases/nitrilases, the predicted 3-dimensional structure of biotinidase is probable and should be useful providing clues to structure-function relationships and ultimately the effect of mutations on altering the enzyme's hydrolase and transferase activities.