Biotinidase Activity Research Articles

Neonatal screening for profound biotinidase deficiency in the Netherlands: consequences and considerations

Biotinidase deficiency is a rare inherited metabolic disorder that can cause severe neurological symptoms. To prevent severe clinical presentations, it was included in the Dutch neonatal screening programme in 2007. Since then the number of cases detected has been high. This study set out to describe the incidence of the disease, the clinical and demographic characteristics of the neonates identified and the type of mutations found. In the south-western Netherlands, 304 982 neonates were screened between 2007 and 2012; and 92 were identified for further testing. Confirmatory testing revealed 6 (7%) with a profound biotinidase deficiency (<10% enzyme activity), 44 (48%) with a partial deficiency (10-30%) and 42 (46%) with normal activity (>30%). All six patients whose profound deficiency was confirmed had enzyme activities below 15% on neonatal screening. Mutation analysis was performed in 61 neonates: 5 'profound', 35 'partial' and 21 'normal'. All five 'profound' cases had two severe mutations. Comparison with the northern Netherlands showed that the frequency and types of mutation were representative for the Netherlands as a whole. The most common mutation detected was c.[1330G>C] (p.(Asp444His); 34%), which is considered to be mild, followed by three severe mutations c.[1368A>C], c.[1595C>T] and c.[1330G>C;511G>A]. Seven new mutations were identified. We conclude that neonatal screening for profound biotinidase produces a high number of false positives. Biotinidase deficiency was profound in less than 10% of cases identified. As biotinidase activity lay below 15% on neonatal screening in all such cases, the screening threshold might be reduced to 15%.

Advances in studies on biotinidase deficiency

Biotinidase deficiency is an autosomal recessive genetic disease with the decrease of biotinidase activity, which is caused by mutations of biotinidase gene.In recent years, with the development of genetic metabolic disease screening, biotinidase deficiency has been diagnosed constantly.Its incidence is about 1∶60 000 persons overseas and its clinical manifestations are complicated with high mortality and morbidity.In this paper, advances on pathogenesis, clinical manifestations, diagnosis and treatment of biotinidase deficiency will be reviewed. Key words: Biotinidase deficiency; Biotinidase gene; Clinical manifestation; Treatment

Comparison of Spectrophotometric and Fluorimetric Methods in Evaluation of Biotinidase Deficiency.

SummaryBackgroundBiotin, a water-soluble vitamin, is used as a co-factor by enzymes involved in carboxylation reactions. Biotinidase (BTD) catalyzes the recycling of biotin from endogenous and dietary sources. Biotinidase deficiency (BD) is an autosomal recessively inherited disorder of biotin recycling that is associated with neurologic and cutaneous consequences when untreated. The aim of the study was to compare the results of spectrophotometric and fluorimetric methods, as well as to evaluate the advantages and disadvantages of both methods in current research practices.MethodsStudy group was chosen among the BD suspected newborn, children and parents (n = 52) who applied to Hacettepe University Pediatric Metabolism Unit.ResultsBTD activity is stable for 2 hours at room temperature and at 4 °C, and for 4 months at –20 °C and –80 °C. Genetic and clinical results showed that 25% of the total number of patients had complete BD which was treated with 10 mg/day biotin, while 15.38% of the patients had partial BD, and they were prescribed biotin 5 mg/day. The area under the ROC curve was 0.960±0.25 and 0.927± 0.41 for the fluorimetric and spectrophotometric method, respectively. Fluorimetric method showed 100% sensitivity and 97% specificity, whereas spectrophotometric method showed 90.5% sensitivity and 93.7% specificity.ConclusionsFluorimetric method is superior to the spectrophotometric method due to higher sensitivity and specificity.

Effects of Biotin Deficiency on Biotinylated Proteins and Biotin-Related Genes in the Rat Brain.

Biotin is a water-soluble vitamin that functions as a cofactor for biotin-dependent carboxylases. The biochemical and physiological roles of biotin in brain regions have not yet been investigated sufficiently in vivo. Thus, in order to clarify the function of biotin in the brain, we herein examined biotin contents, biotinylated protein expression (e.g. holocarboxylases), and biotin-related gene expression in the brain of biotin-deficient rats. Three-week-old male Wistar rats were divided into a control group, biotin-deficient group, and pair-fed group. Rats were fed experimental diets from 3 wk old for 8 wk, and the cortex, hippocampus, striatum, hypothalamus, and cerebellum were then collected. In the biotin-deficient group, the maintenance of total biotin and holocarboxylases, increases in the bound form of biotin and biotinidase activity, and the expression of an unknown biotinylated protein were observed in the cortex. In other regions, total and free biotin contents decreased, holocarboxylase expression was maintained, and bound biotin and biotinidase activity remained unchanged. Biotin-related gene (pyruvate carboxylase, sodium-dependent multivitamin transporter, holocarboxylase synthetase, and biotinidase) expression in the cortex and hippocampus also remained unchanged among the dietary groups. These results suggest that biotin may be related to cortex functions by binding protein, and the effects of a biotin deficiency and the importance of biotin differ among the different brain regions.

Quantitative Analytical Method for the Determination of Biotinidase Activity in Dried Blood Spot Samples.

Biotinidase activity assay is included in most newborn screening protocols, and the positive results are confirmed by quantitative enzyme activity measurements. In our study, we describe a new quantitative analytical method for the determination of biotinidase activity using the blood sample deposited onto filter paper as the assay medium, by predepositing N-biotinyl-p-aminobenzoic acid onto the standard sample collection paper. The analysis of the assay mixture requires a simple extraction step from a dried blood spot followed by the quantification of product by LC-MS. The method provides a simple and reliable enzyme assay method that enables the rapid diagnosis of biotinidase deficiency (BD). Out of the measured 36 samples, 13 were healthy with lower enzyme activities, 16 were patients with partial BD, and 7 were patients with profound BD with residual activity below 10%. Expression of enzyme activity in percentage of mean activity of negative controls allows comparison of the different techniques. The obtained results are in good agreement with activity data determined from both dried blood spots and serum samples, giving an informative diagnostic value.

Outcomes of oral biotin treatment in patients with biotinidase deficiency — Twenty years follow-up

IntroductionBiotinidase deficiency (BTD) is an inborn error of biotin metabolism inherited as an autosomal recessive trait. Due to the, biotinidase deficiency, biotin is not recycled. Individuals with BTD usually exhibit neurological and cutaneous abnormalities unless treated with biotin. Supplementation with biotin may either ameliorate or if early introduced even prevent symptoms when introduced presymptomatically. Patients and methodsSince 1991, 22 Polish patients from 19 families have been diagnosed with BTD. In 16 children the diagnosis had been suspected on the basis of clinical signs: skin lesions, hyperventilation, seizures, spasticity, and laboratory investigation (elevated lactate and metabolites on urine organic acids profile).The defect was enzymatically (serum biotinidase activity measurement) and genetically (tested for mutations in the BTD gene) confirmed afterwards. All patients were treated with biotin. Urine organic acids analysis (GC/MS) for 3-hydroxizovaleric acid was used for patients' monitoring. Neurological, audiological and ophthalmological evaluation has been conducted once a year. ResultsIn 5 symptomatic patients a progressive optic nerve atrophy had already been noted at the time of treatment initiation. In these patients sensorineural hearing loss has also been diagnosed despite biotin supplementation. Asymptomatic patients treated with biotin supplementation presented no signs or symptoms of BTD. Supplementation with biotin slows the progression of BTD in symptomatic patients, but does not reverse nerve atrophy. Nonetheless, introduction of the treatment with biotin during presymptomatic stage of the disease prevents the onset of symptoms including optic atrophy and hearing loss. Homozygosity for the p.Leu215Phe mutation in BTD gene seems to be frequent in patients from the North-Eastern region of Poland and is connected with the hearing loss. ConclusionSince the prognosis for individuals diagnosed with BTD is good, provided they are treated before symptoms occur, it is justified to add this metabolic disorder to the panel of conditions screened under the national newborn screening programme in Poland.

Biotinidase deficiency: Spectrum of molecular, enzymatic and clinical information from newborn screening Ontario, Canada (2007-2014).

Untreated profound biotinidase deficiency results in a wide range of clinical features, including optic atrophy, cutaneous abnormalities, hearing loss and developmental delay. Ontario, Canada incorporated this treatable deficiency in newborn screening over the past 8years. This study elucidates the molecular, biochemical, and clinical findings from the pilot project. Information from initial screens, serum biotinidase activity level assays, molecular testing, and family history for 246 positive newborns screens were analyzed. A mutation spectrum was created for the province of Ontario, including common mutations such as D444H, D444H/A171T, Q456H, C33fs, and R157H. Individuals with partial deficiency were separated into 3 groups: D444H homozygotes (Group 1); compound heterozygotes for D444H with another profound allele (Group 2); compound heterozygotes with two non-D444H alleles (Group 3). Biochemical phenotype-genotype associations in partial deficiency showed a significant difference in serum biotinidase activity in between any given two groups. Three children with partial deficiency discontinued biotin for varied lengths of time. Two of whom became symptomatic with abnormal gait, alopecia, skin rashes and developmental delay. A need for more congruency in diagnostic, treatment and educational practices was highlighted across the province. Heterogeneity and variation in clinical presentations and management was observed in patients with the partial deficiency.

The importance of developing novel diagnostic tools for congenital metabolic disorders

Babies are not little adults. This frequently repeated statement implies that to develop accurate diagnostic methods to identify potentially catastrophic disorders, it is not sufficient to just wait until permanent changes have occurred and are clearly recognized by physicians in clinical practice. This is the position of many organizations that advocate on behalf of children [1]. Moreover, in the United States, the Food and Drug Administration grants approvals for diagnostic tools based on the populations in which they were studied. One of such examples is biotinidase deficiency. This autosomal recessive disorder has an estimated prevalence of 1 in 60,000 cases [2,3]. Most affected infants become symptomatic in the first months of life and are characterized by abnormal respiratory drive, hypotonia, failure to thrive, seborrheic dermatitis like-rash, progressive developmental delay, and myoclonic seizures. If untreated, this leads to a static-encephalopathy picture and significant motor and metal handicaps with subsequent significant morbidity and mortality and the increased costs for health care support [4]. The pathogenesis of this disease is secondary to a profound deficiency (less than 10% of enzyme activity) of biotinidase. This enzyme has ubiquitous distribution and is essential for the recycling of biotin by releasing it from any of the four holo-carboxylases: pyruvate, acetyl-CoA, propionyl-CoA, and 3-methylcrotonyl [5]. Treatment with biotin leads to a significant response and resolution of symptoms. Therefore, early diagnosis and identification of asymptomatic subjects is of the utmost importance in order to establish rapid treatment and prevent the neurological consequences of this disorder. Most laboratories typically rely on a semi-quantitative analysis for screening of this disorder in the newborn period by testing colorimetric changes of biotinidase enzyme activity in dried blood samples (DBS). However, this approach opens the possibility of impaired quality of enzyme activity in the sample, with the caveat that the mutant DNA remains relatively intact [6]. Consequently, there is a growing interest on developing more precise or adjunctive methodologies for more accurate and rapid diagnosis of this and other potentially treatable disorders. Therefore, the Lindau-Shepard et al. [7] study is a welcome addition to our understanding of diagnostic methods in the newborn period using molecular genotyping and illustrates the advantages of developing supplemental screening tools. Historically, the use of real time *Corresponding author: Edgard Andrade, University of Florida, Department of Pediatrics, Division of Neurology, PO Box 100296, Gainesville, FL 32610, USA. Tel.: +1 352 273 5778; Fax: +1 352 392 9802; E-mail: andrade@peds.ufl.edu. Journal of Pediatric Genetics 1 (2012) 149–151 DOI 10.3233/PGE-2012-024 IOS Press 149

Improved Identification of Partial Biotinidase Deficiency by Newborn Screening Using Age-Related Enzyme Activity Cutoffs: Reduction of the False-Positive Rate

Background: Biotinidase deficiency is an inherited metabolic disorder that if untreated can result in neurological and cutaneous features. Profound biotinidase deficiency presents in early childhood with severe symptoms, whereas partial biotinidase deficiency can also present with symptoms under times of stress. Symptoms can be prevented by administering biotin. Newborn screening for the disorder is performed using dried blood spots. We examined the relationship between biotinidase activity and age at collection to determine how best to identify infants with partial biotinidase deficiency. Methods: Biotinidase activity in dried blood spots is determined using a quantitative fluorometric assay. Subsequent specimens with biotinidase activity ≤100 U were analyzed by mutation analysis to determine the range of activities expressed in infants with partial biotinidase deficiency. Results: Enzyme activity increased with age, beginning at about three days of age, and rose until plateauing at about 11 days of age. An increase of about 47.6% was observed. A total of 54 specimens had mutation analysis performed identifying 20 affected infants who would not have been identified using the original cutoff activity of 50 U. Conclusion: Biotinidase activity in infants increases with age. Age-related cutoffs assist in selectively identifying infants with partial biotinidase deficiency.

PP01.1 – 2565: Next generation sequencing analysis in neonatal/early epileptic encephalopathy

Objective Epileptic encephalopathy (EE) term describes epilepsy syndromes in which seizures and epileptiform electroencephalographic abnormalities are considered to contribute to progressive cerebral dysfunction. A subset of all the EEs that still await an etiological explanation, particularly those with onset of seizures within the first year of life. In this study genetic backround of neonatal/early infantile EE was investigated by next generation sequencing (NGS) analysis. Methods Thirty cases who had refractory seizures with neonatal or early infantile onset were prospectively included in this study. Three cases had history of hospitalization in neonatal unit due to meconium aspiration syndrome, and four cases also had cyanosis and/or transient respiratory distress following the labor. All cases had normal metabolic work up including serum lactic acid, pyruvic acid, aminoacid and carnitine levels, biotinidase activity and urine organic acids. Their cranial magnetic resonance imaging findings were normal except cerebral atrophy. Their karyotype analyses were normal. None of them had antiquitin gene mutation. Mutations in 16 genes (ARX, CDKL5, CNTNAP2, FOLR1, FOXG1, GRPR, LAMC3, MBD5, MECP2, PCDH19, PNKP, SCN1A, SCN1B, SCN2A, STXBP1, KCNQ2) were examined with NGS method in our cases. Results Ages ranged between 6–204 (62.5±51.6) months. Parental consanguinity was found in 11 of 30 cases (36%). Seizures started between 1–270 (91.7±80.25) days of life, eleven cases had seizures with neonatal onset. Infantile spasms were the predominant seizure type in our group consisting of 16 of 30 cases. All of them were treated with at least two anticonvulsant drugs. Cranial magnetic resonance imaging was normal in half of the cases, the reminder had cortical or cerebellar atrophy. The results of NGS analysis were discussed with the literature. Conclusion We believe that NGS screening will soon contribute to pediatric neurologists to diagnose children with epilepsies of unknown etiology.

Why screen newborns for profound and partial biotinidase deficiency?

Newborn screening for biotinidase deficiency is currently performed throughout the United States and inmany countries of the world. However, there are still many countries that do not screen for the disorder. After learning howmany countries are still not screening for biotinidase deficiency, and after I received the comments on a recently submitted publication, I was compelled to address twomajor concerns about newborn screening for the disorder. The first is why should a country screen their newborns for profound biotinidase deficiency (less than 10% of mean normal serum enzyme activity)? The second is, if a country screens their newborns for profound biotinidase deficiency, why should they also screen for partial biotinidase deficiency (between10% and 30% of mean normal serum enzyme activity)? Before addressing these issues, Iwould like to state that over thepast 32 years, my research has focused on the study of the clinical, biochemical and molecular aspects of biotinidase deficiency. Even though my laboratory developed the colorimetric assay for biotinidase activity using blood-soaked filter paper cards, and we conducted the first newborn screening program in Virginia, I have not received, nor do I currently receive, any compensation for any aspect of newborn screening of the disorder. This being said, I would like to address the above questions. Why screen newborns for profound biotinidase deficiency? Since the discovery of biotinidase deficiency in our laboratory in 1982 [1,2], there has been a rapid transition from the development of a colorimetric method for determining biotinidase activity using blood-soaked filter paper spots [3] to the demonstration of the feasibility of performing

Edaravone, a free radical scavenger, protects liver against valproic acid induced toxicity

Valproic acid (VPA), is a well established anticonvulsant drug that has been increasingly used in the treatment of many forms of generalized epilepsy. Edaravone (EDA; 3-methyl-1-phenyl-2-pyrazoline-5-one) is a potent free radical scavenger. In this study, we aimed to investigate the effects of EDA on VPA-induced hepatic damage. Male Sprague Dawley rats were divided into four groups. Group I was control animals. Group II was control rats given valproic acid (500 mg kg-1 day) for seven days. Group III was given only EDA (30 mg kg-1day) for seven days. Group IV was given VPA+EDA (in same dose and time). EDA and VPA were given intraperitoneally. On the 8th day of experiment, blood samples and liver tissue were taken. Serum aspartate and alanine aminotransferase, alkaline phosphatase and bilirubin levels, liver myeloperoxidase, xanthine oxidase, adenosine deaminase, Na+/K+ATPase, sorbitol dehydrogenase, glutamate dehydrogenase, DT-diaphorase, arginase and thromboplastic activities, lipid peroxidation, protein carbonyl levels were increased whereas paraoxonase, biotinidase activities and glutathione levels were decreased in VPA group. Application of EDA with VPA protected against VPA-induced effects. These results demonstrated that administration of EDA is a potentially beneficial agent to reduce hepatic damage in VPA induced hepatotoxicity, probably by decreasing oxidative stress.

Inborn Errors of Metabolism in the United Arab Emirates: Disorders Detected by Newborn Screening (2011-2014).

This study reports on the inborn errors of metabolism (IEM) detected by our national newborn screening between 2011 and 2014. One hundred fourteen patients (55 UAE citizens and 59 residents) were diagnosed during this period. The program was most comprehensive (tested 29 IEM) and universally applied in 2013, giving an incidence of 1 in 1,787 citizens. This relatively high prevalence resulted from the frequent consanguineous marriages (81.5%) among affected families. The following eight disorders accounted for 80% of the entities: biotinidase deficiency (14 of 55), phenylketonuria (11 of 55), 3-methylcrotonyl glycinuria (9 of 55), medium-chain acyl-CoA dehydrogenase deficiency (4 of 55), argininosuccinic aciduria, glutaric aciduria type 1, glutaric aciduria type 2, and methylmalonyl-CoA mutase deficiency (2 of 55 each). Mutation analysis was performed in 48 (87%) of the 55 patients, and 33 distinct mutations were identified. Twenty-nine (88%) mutations were clinically significant and, thus, could be included in our premarital screening. Most mutations were homozygous, except for the biotinidase deficiency. The BTD mutations c.1207T>G (found in citizens) and c.424C>A (found in Somalians) were associated with undetectable biotinidase activity. Thus, the high prevalence of IEM in our region is amenable to newborn and premarital screening, which is expected to halt most of these diseases.

Biotinidase deficiency: clinical and genetic studies of 38 Brazilian patients.

BackgroundBiotinidase deficiency (BD) is an inborn error of metabolism in which some genetic variants correlate with the level of enzyme activity. Biotinidase activity, however, may be artifactually low due to enzyme lability, premature birth, and jaundice; this hinders both phenotypic classification and the decision to implement therapy. This study sought to characterize the clinical and genetic profile of a sample of Brazilian patients exhibiting reduced biotinidase activity.MethodsThis observational, multicenter study used a convenience sampling strategy, with sequencing of exons 2, 3, and 4 of the BTD gene.ResultsThe sample comprised 38 individuals with biochemical phenotypes defined a priori on the basis of biotinidase activity in serum/plasma (2 with profound deficiency, 9 with partial deficiency, 15 heterozygous, 1 borderline between partial deficiency and heterozygosity, 2 borderline between heterozygous and normal) or dried blood spot sample (n = 9, all with unspecified deficiency). Most patients were from Southern Brazil (n = 29/38) and were identified by neonatal screening (n = 33/38). Parental consanguinity was reported in two cases. The most commonly found genetic variants were c.1330G > C (p.D444H), c.755A > G (p.D252G), and c.[511G > A;1330G > C] (p.[A171T;D444H]), with allele frequencies of 50%, 9.4%, and 5.4% respectively. Three novel pathogenic variants were identified (c.119 T > C or p.L40P, c.479G > A or p.C160Y, and c.664G > A or p.D222N). Twenty-nine patients had two pathogenic variants detected (with cis/trans status ascertained in 26/29), six had only one variant, and three had no pathogenic variants detected. Genotyping confirmed the original phenotypic classification based on enzyme activity in 16/26 cases. Three polymorphic variants were identified in control individuals, of which two were nonpathogenic (c.1171C > T or p.P391S and c.1413 T > C or p.C471C, with a frequency of 1.5% and 5.5% respectively) and one pathogenic (c.1330G > C, frequency 4%).ConclusionsOur findings suggest that partial BD is the most common form of BD in Brazil, and expand current knowledge on the allelic heterogeneity of this condition.

Evaluation of a fluorometric method for semi-quantitative determination of biotinidase activity in newborn dried bloodspots on the Wallac VICTOR2 automated platform and establishment of biotinidase stability and reference intervals

Evaluation of a fluorometric method for semi-quantitative determination of biotinidase activity in newborn dried bloodspots on the Wallac VICTOR2 automated platform and establishment of biotinidase stability and reference intervals

Novel mutations causing biotinidase deficiency in individuals identified by newborn screening in Michigan including an unique intronic mutation that alters mRNA expression of the biotinidase gene

Biotinidase deficiency (BD) is an autosomal recessive disorder resulting in the inability to recycle the vitamin biotin. Individuals with biotinidase deficiency can develop neurological and cutaneous symptoms if they are not treated with biotin. To date, more than 165 mutations in the biotinidase gene (BTD) have been reported. Essentially all the mutations result in enzymatic activities with less than 10% of mean normal serum 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 and causes partial biotinidase deficiency (10–30% of mean normal serum biotinidase activity) if there is a mutation for profound biotinidase deficiency on the second allele. We now reported eight novel mutations in ten children identified by newborn screening in Michigan from 1988 to the end of 2012. Interestingly, one intronic mutation, c.310-15delT, results in an approximately two-fold down-regulation of BTD mRNA expression by Quantitative real-time reverse-transcription PCR (qRT-PCR). This is the first report of an intronic mutation in the BTD gene with demonstration of its effect on enzymatic activity by altering mRNA expression. This study identified three other mutations likely to cause partial biotinidase deficiency. These results emphasize the importance of full gene sequencing of BTD on patients with biotinidase deficiency to better understand the genotype and phenotype correlation in the future.

Characterization and functional analysis of cellular immunity in mice with biotinidase deficiency

Biotinidase deficiency is an autosomal recessively inherited metabolic disorder that can be easily and effectively treated with pharmacological doses of the vitamin, biotin. Untreated children with profound biotinidase deficiency may exhibit neurological, cutaneous and cellular immunological abnormalities, specifically candida infections. To better understand the immunological dysfunction in some symptomatic individuals with biotinidase deficiency, we studied various aspects of immunological function in a genetically engineered knock-out mouse with biotinidase deficiency. The mouse has no detectable biotinidase activity and develops neurological and cutaneous symptoms similar to those seen in symptomatic children with the disorder. Mice with profound biotinidase deficiency on a biotin-restricted diet had smaller thymuses and spleens than identical mice fed a biotin-replete diet or wildtype mice on either diet; however, the organ to body weight ratios were not significantly different. Thymus histology was normal. Splenocyte subpopulation study showed a significant increase in CD4 positive cells. In addition, in vitro lymphocyte proliferation assays consistently showed diminished proliferation in response to various immunological stimuli. Not all symptomatic individuals with profound biotinidase deficiency develop immunological dysfunction; however, our results do show significant alterations in cellular immunological function that may contribute and/or provide a mechanism(s) for the cellular immunity abnormalities in individuals with biotinidase deficiency.

Biotinidase knockout mice show cellular energy deficit and altered carbon metabolism gene expression similar to that of nutritional biotin deprivation: Clues for the pathogenesis in the human inherited disorder

Biotin is the prosthetic group of carboxylases that have important roles in the metabolism of glucose, fatty acids and amino acids. Biotinidase has a key role in the reutilization of the biotin, catalyzing the hydrolysis of biocytin (ε-N-biotinyl-l-lysine) and biocytin-containing peptides derived from carboxylase turnover, thus contributing substantially to the bioavailability of this vitamin. Deficient activity of biotinidase causes late-onset multiple carboxylase in humans, whose pathogenic mechanisms are poorly understood. Here we show that a knock-out biotinidase-deficient mouse from a C57BL/6 background that was fed a low biotin diet develops severe ATP deficit with activation of the energy sensor adenosine monophosphate (AMP)-activated protein kinase (AMPK), inhibition of the signaling protein mTOR, driver of protein synthesis and growth, and affecting the expression of central-carbon metabolism genes. In addition, sensitivity to insulin is augmented. These changes are similar to those observed in nutritionally biotin-starved rats. These findings further our understanding of the pathogenesis of human biotinidase deficiency.

High incidence of partial biotinidase deficiency cases in newborns of Greek origin

Biotinidase deficiency (BTD) is an inherited disorder with severe clinical manifestations if not treated early. 63,119 neonates were tested for BTD according to a 3-step protocol. Biotinidase activity was initially estimated through standard colorimetric method on dried blood spots, then the suspected samples were subjected to molecular analysis of the BT gene and determination of BT activity in serum through an HPLC method. 14 infants with partial BTD (incidence 1:4508) were detected. Nine of them were homozygotes (D444H/D444H), and 4 compound heterozygotes carrying D444H combined with Q456H, T532M, C186Y and R157H, respectively. All were asymptomatic and supplemented with 10mg biotin. Although the number of screened neonates is rather small, it may be suggested that the incidence of the partial BTD infants is the highest ever reported. Detection of BTD should be added to the Greek national neonatal screening program.

Periorificial Dermatitis and Erosive Inguinal Plaques in a 57-Year-Old Woman—Quiz Case

A 7-year-old girl presented with complaints of hair loss and a known partial biotinidase deficiency since birth. Biotin supplementation was discontinued after the first year of life because clinical manifestations were absent, and laboratory findings were normal. At age 2 years, hair loss and eczema occurred. Owing to low biotinidase activity, biotin supplementation, 20 mg/wk, was restarted, but it was again discontinued at age 3 years because normal biotin levels had been achieved once more. The patient showed a normal physical and mental development, but hair loss continued. Clinical examination revealed dense but short and brittle terminal hairs of different lengths with white nodes along the lengths of hair shafts (Figure 1). No other pathologic findings were seen on the scalp, and results of the hair-pull test were negative. Light microscopy analysis of the longitudinal embedded hair was carried out (Figure 2). The biotin supplementation dose at last follow-up was 5 mg/wk. What is your diagnosis?