Biotin Homeostasis and Human Disorders: Recent Findings and Perspectives.

Biotin (vitamin B7, or vitamin H) is a water-soluble B-vitamin that functions as a cofactor for carboxylases, i.e., enzymes involved in the cellular metabolism of fatty acids and amino acids and in gluconeogenesis; moreover, as reported, biotin may be involved in gene regulation. Biotin is not synthesized by human cells, but it is found in food and is also produced by intestinal bacteria. Biotin status/homeostasis in human individuals depends on several factors, including efficiency/deficiency of the enzymes involved in biotin recycling within the human organism (biotinidase, holocarboxylase synthetase), and/or effectiveness of intestinal uptake, which is mainly accomplished through the sodium-dependent multivitamin transporter. In the last years, administration of biotin at high/"pharmacological" doses has been proposed to treat specific defects/deficiencies and human disorders, exhibiting mainly neurological and/or dermatological symptoms and including biotinidase deficiency, holocarboxylase synthetase deficiency, and biotin-thiamine-responsive basal ganglia disease. On the other hand, according to warnings of the Food and Drug Administration, USA, high biotin levels can affect clinical biotin-(strept)avidin assays and thus lead to false results during quantification of critical biomarkers. In this review article, recent findings/advancements that may offer new insight in the abovementioned research fields concerning biotin will be presented and briefly discussed.

Biotinidase biochemical and molecular analyses: Experience at a large reference laboratory.

BACKGROUND: Biotinidase deficiency is caused by absent activity of the biotinidase, encoded by the biotinidase gene (BTD). Affected individuals cannot recycle the biotin, leading to heterogeneous symptoms that are primarily neurological and cutaneous. Early treatment with biotin supplementation can prevent irreversible neurological damage and is recommended for patients with profound deficiency, defined as enzyme activity <10% mean normal (MN). Molecular testing has been utilized along with biochemical analysis for diagnosis and management. In this study, our objective was to correlate biochemical phenotype/enzyme activity to BTD genotype in patients for whom both enzyme and molecular testing were performed at our lab, and to review how the correlations inform on variant severity. METHODS: We analyzed results of biotinidase enzyme analysis and BTD gene sequencing in 407 patients where samples were submitted to our laboratory from 2008 to 2020. RESULTS: We identified 84 BTD variants; the most common was c.1330G>C, and 19/84 were novel BTD variants. A total of 36 patients had enzyme activity <10% of MN and the most common variant found in this group was c.528G>T. No variant was reported in one patient in the profound deficiency group. The most common variant found in patients with enzyme activity more than 10% MN was c.1330G>C. CONCLUSIONS: Although enzyme activity alone may be adequate for diagnosing profound biotinidase deficiency, molecular testing is necessary for accurate carrier screening and in cases where the enzyme activity falls in the range where partial deficiency and carrier status cannot be discriminated.

Ophthalmic manifestations of biotinidase deficiency: report of a case and review of literature.

INTRODUCTION: Biotinidase deficiency (BD) is an inherited autosomal recessive metabolic disorder. BD has been associated with optic nerve atrophy, eye infections, and retinopathy. The most prevalent ophthalmic manifestation of BD is optic atrophy, which might be misdiagnosed as multiple sclerosis or neuromyelitis optica, especially in late-onset BD cases. METHODS: In this article, we report a 9-year-old boy with gradual vision loss. Ophthalmologic examination, Brain MRI, and several laboratory tests such as Aquaporin-4 IgG level and biotinidase level were done on the patient. RESULTS: Bilateral optic atrophy and impaired visual acuity were detected on examination. The patient had a biotin level of 1.25 U/min/ml (normal range 3-9 U/min/ml), favoring the BD. CONCLUSION: In this study, we report a 9-year-old boy with vision loss diagnosed with BD. We also reviewed the literature to highlight the ophthalmic manifestations of BD. Ophthalmologists must consider BD in children with unexplained ophthalmologic complaints, especially when other characteristic signs of BD (e.g., developmental delay, seizure) are present. Also, patients with BD should undergo regular annual ophthalmologic examinations to be checked for any signs of eye involvement.

Evaluation of clinical, laboratory, and molecular genetic features of patients with biotinidase deficiency.

Biotinidase deficiency (BD) is an autosomal recessive inherited metabolic disorder which results from the inability of biotin-dependent carboxylase enzymes to function due to the release and absorption of biotin, leading to neurological and cutaneous findings. In the present study, evaluation of demographic characteristics, clinical findings, laboratory results, molecular genetic characteristics, and genotype-phenotype correlations of cases with BD. Two hundred forty-seven cases were included in the study who were admitted to the Department of Pediatric Metabolism of Ankara Bilkent City Hospital after being identified with potential BD through the Newborn Screening Program (NBS), during family screening or based on suspicious clinical findings, or following the detection of a pathogenic variant in a BTD genetic analysis during the period of October 2020 and February 2022. The medical files of the cases were reviewed retrospectively. An analysis of the admission routes of all cases to our clinic revealed 89.5% NBS, 5.7% family screening, and 4.9% suspicious clinical findings suggestive of BD. Complete enzyme deficiency was identified in 19.8%, partial enzyme deficiency in 55.1%, and heterogenous enzyme deficiency in 9.7%. The most common pathogenic variants were c.1270G > C (p.Asp424His), c.410G > A (p.Arg137His), and c.38_44delGCGCTGinsTCC (p.Cys13Phefs*36) in BTD gene. The c.1270G > C variant was most common in patients with cutaneous symptoms. The c.410G > A and c.38_44delGCGCTGinsTCC variants were more common in the patients with neurological symptoms. The mean activity level in patients with the c.1270G > C homozygous variant was statistically significantly higher than the mean activity level in the c.1270G > C compound heterozygous patients and the activity level of patients without the c.1270G > C variant. The mean activity level in c.410G > A homozygous patients was statistically significantly lower than the mean activity level of the c.410G > A compound heterozygous patients and the activity level of patients without the c.410G > A variant. In the course of our study, four new pathogenic variants were detected, namely: c.190G > A (p.Glu64Lys), c.249 + 5G > T, c.228delA (p.Val77*), and c.682A > G (p.Ile228Val).     Conclusions: The present study has determined the clinical and genetic spectrum of a large group of patients with BD in a single center. The frequent mutations in our study were similar to those reported in literature, and four novel variants were also described. What is Known: • Biotinidase deficiency is an autosomal recessive, treatable inborn error of metabolism. Two hundred ninety-four pathogenic variants in the BTD gene have been identified and the c.1270G > C variant is the most frequent BTD gene mutation in both Turkey and around the world. What is New: • Four new pathogenic variants (c.190G > A, p.Glu64Lys; c.249 + 5G > T; c.228delA, p.Val77*; and c.682A > G, p.Ile228Val) have been identified. It is believed that the c.38_44delGCGGCTGinsTCC variant is more commonly seen in individuals with ocular issues; however, further genotype-phenotype correlations are needed.

Biotinidase Deficiency in the Second Decade with Atypical Neuroimaging Findings.

Biotinidase deficiency is a rare autosomal recessive neurometabolic disorder resulting in biotin deficiency. Our patient presented with seizures and developmental delay since infancy and was started on megavitamin supplements. At 14 years, she presented with motor regression with encephalopathy after discontinuation of vitamins. There were no skin and hair changes. Magnetic resonance imaging (MRI) of the brain showed bilateral symmetrical posterior putamen signal changes. Tandem mass spectroscopy showed increased methyl malonyl carnitine and 3-OH isovaleryl carnitine. There was a low biotinidase level, and a pathogenic variant in the BTD gene in the next-generation sequencing was identified. Special importance is placed on the unusual symmetric posterior putamen involvement seen in MRI of the brain.

Delayed Biotin Therapy in a Child with Atypical Profound Biotinidase Deficiency: Late Arrival of the Truth and a Lesson Worth Thinking.

Biotinidase (BTD) deficiency (OMIM 253260) is an autosomal recessively inherited metabolic disorder resulting from deficient activity of the BTD enzyme, which can cleave and release biotin from a variety of biotin-dependent carboxylases, and is therefore recognized as a tool to recycle biotin. Being a condition caused by variations on BTD gene with a consequence of free biotin shortage, BTD deficiency may impair the activity of biotin-dependent carboxylases, and thus bring about a buildup of potentially toxic compounds in the body, primarily 3-hydroxyisovaleryl-carnitine in plasma as well as 3-hydroxyisovaleric acid in urine. The phenotype of BTD deficiency may vary dramatically, from asymptomatic adults to severe neurological anomalies, even death in infancy. In the present study, we reported on a 5-month-old boy, whose parents sought for medical consultation in our clinic for their son due to his loss of consciousness, repeated tetany, and motor retardation. Detailed clinical features included severe psychomotor retardation, hypotonia, as well as failure to thrive. The brain MRI at 12 months showed cerebellar hypoplasia and multiple foci of leukodystrophy. The result of antiepileptic therapy was not satisfying. During hospitalization, BTD deficiency was suggested by elevated concentration of 3-hydroxyisovaleryl-carnitine in the blood spots and 3-hydroxyisovaleric acid in the urine. The child was then diagnosed with profound BTD deficiency based on the above findings and low BTD enzyme activity. Subsequent mutational analysis revealed a novel homozygous variant, c.637_637delC (p.H213Tfs*51) in exon 4 of BTD gene in the proband, which was recognized as a further support to the diagnosis. Therefore, biotin treatment was started immediately, eventually with satisfactory outcomes achieved in terms of prevention of epileptic seizure, performance in deep tendon reflexes, and improvement of muscular hypotonia, but unfortunately, the therapy failed to show any evident effects on poor feeding and intellectual disability. This painful lesson suggests that newborn screening for inherited metabolic diseases is essential for early identification and treatment, which should have been performed in this case to avoid this tragedy.

Identification and characterization of the largest deletion in the PCCA gene causing severe acute early-onset form of propionic acidemia.

Whole-exome sequencing (WES) is an excellent method for the diagnosis of diseases of uncertain or heterogeneous genetic origin. However, it has limitations for detecting structural variations such as InDels, which the bioinformatics analyzers must be aware of. This study aimed at using WES to evaluate the genetic cause of the metabolic crisis in a 3-day-old neonate admitted to the neonatal intensive care unit (NICU) and deceased after a few days. Tandem mass spectrometry (MS/MS) showed a significant increase in propionyl carnitine (C3), proposing methylmalonic acidemia (MMA) or propionic acidemia (PA). WES demonstrated a homozygous missense variant in exon 4 of the BTD gene (NM_000060.4(BTD):c.1330G > C), responsible for partial biotinidase deficiency. Segregation analysis of the BTD variant revealed the homozygous status of the asymptomatic mother. Furthermore, observation of the bam file, around genes responsible for PA or MMA, by Integrative Genomics Viewer (IGV) software displayed a homozygous large deletion in the PCCA gene. Comprehensive confirmatory studies identified and segregated a novel outframe deletion of 217,877 bp length, "NG_008768.1:g.185211_403087delinsTA", extended from intron 11 to 21 of the PCCA, inducing a premature termination codon and activation of nonsense-mediated mRNA decay (NMD). Homology modeling of the mutant PCCA demonstrated eliminating the protein's active site and critical functional domains. Thereupon, this novel variant is suggested as the largest deletion in the PCCA gene, causing an acute early-onset PA. These results could expand the PCCA variants spectrum, and improve the existing knowledge on the molecular basis of PA, as well as provide new evidence of pathogenicity of the variant (NM_000060.4(BTD):c.1330G > C.

Tetraparesis as an initial manifestation of biotinidase deficiency: a case report.

Biotinidase deficiency (BTD) is an autosomal recessive disorder and causes the deficiency of four biotin-containing carboxylases. The prevalence is estimated at 1 in 60 000 births. BTD is associated with a wide spectrum of clinical manifestations, including abnormalities of the neurological, dermatological, immunological, and ophthalmological systems. Spinal cord demyelination as a manifestation of BTD has been infrequently described. Case presentation: The authors present a case of 2.5-year-old boy complained of progressive weakness in all four limbs, with difficulties in breathing. Clinical discussion: Abdominal examination revealed hepatomegaly and splenomegaly. Also, her parents were first-degree cousins. Therefore, tandem mass spectroscopy and urine organic acid analysis were planned to exclude metabolic disorders. Urinary organic acid analysis revealed elevated levels of methylmalonic acid and 3-hydroxyisovaleric acid. Serum biotinidase activity was found to be 3.9 nmol/min/ml. Oral biotin at a dose of 1 mg/kg daily was initiated. A marked improvement of his neurological deficit was noted over a period of 15 days after treatment and cutaneous manifestations resolved within 3 weeks. Conclusion: Myelopathy due to BTD is a challenging diagnosis. Spinal cord impairment is a rare complication of this disease and is frequently unrecognized. BTD should be included in the differential diagnosis of children presenting with demyelinating spinal cord disease.

Biotinidase deficiency: What have we learned in forty years?

BACKGROUND: Biotinidase deficiency (BD) is an autosomal recessively inherited disorder that was first described in 1982. Forty years after its first description, we compiled available clinical data on BD with the aim of generating a more comprehensive picture of this condition. METHODS: A systematic search strategy was performed in relevant databases without limits for publication date or languages. We screened 3966 records and included 144 articles reporting individuals with BD and their clinical presentation as well as the outcomes, when available. RESULTS: This study included 1113 individuals with BD. More than half (51.5%) of these individuals were diagnosed by newborn screening, 43.3% in presence of clinical symptoms and 5.2% due to family screening. We grouped symptomatic individuals into four main clinical presentations: neonatal-onset (<1 month; 7.9%), early childhood-onset (<2 years; 59.2%), juvenile-onset (2-16 years; 25.1%) and adult-onset (>16 years; 7.7%). BD affected five main organ systems: nervous system (67.2%), skin (53.7%), eye (34.4%), auditory (26.9%) and respiratory system (17.8%). Involvement was mainly multisystemic (82.2%) of individuals, whereas isolated system presentation was seen in only 17.2% of individuals. When reported, metabolic acidosis was present in 42.4% of symptomatic individuals and characteristic abnormal organic acid metabolites were found in 57.1%. Biotin treatment led to clinical stability or improvement in 89.2% of individuals. 1.6% of reported individuals with BD died due to non-availability of treatment or late diagnosis. CONCLUSION: Newborn screening has had a major positive impact on the outcome of many individuals with BD. However, undiagnosed and non-treated BD remains a health concern. Given the risk of mortality or complications associated with late or missed diagnosis if newborn screening is not available, a trial of biotin should be considered in undiagnosed infants and adults exhibiting suspected clinical signs. Enzymatic activity and/or analysis of genetic variants can readily confirm the diagnosis of BD.

Evaluation of 700 patients referred with a preliminary diagnosis of biotinidase deficiency by the national newborn metabolic screening program: a single-center experience.

OBJECTIVES: This study aimed to investigate the clinical, demographic and laboratory characteristics of the patients referred with a preliminary diagnosis of biotinidase deficiency through the national newborn metabolic screening program. We also attempted to determine the cut-off level of the fluorometric method used for screening biotinidase deficiency by the Ministry of Health. METHODS: A total of 700 subjects who were referred to the Pediatric Metabolism Outpatient Clinic with a preliminary diagnosis of biotinidase deficiency through the national newborn metabolic screening program were retrospectively evaluated. Patients detected by family screening were excluded. Biotinidase enzyme activity was assessed and BTD gene analysis was performed in all patients. RESULTS: Of 700 subjects who were referred by the screening program, 284 (40.5 %) had biotinidase deficiency (BD). The enzyme activity was 0-10, 10-30 and >30 % in 39 (5.5 %), 245 (35 %) and 416 (59.5 %) patients, respectively. The BD was partial in majority of patients (86.2 %). The cut-off level was 59.5 MRU for partial BD and 50.5 MRU for profound BD. The most common mutation detected was p.Arg157His (c.470G>A) among patients with profound BD, and p.D444H (c.1330G>C) among patients with partial BD. CONCLUSIONS: Treatment should be initiated promptly in patients who are referred by the newborn screening program. Any mean activity under 59.5 MRU should be considered partial BD, while less than 50.5 MRU should be considered profound BD. It should be kept in mind that clinical manifestations may develop both in profound and partial BD.

[Holocarboxylase synthetase deficiency induced by HLCS gene mutations: a rare disease study]. / ç½•è§ç— ç ”ç©¶ï¼šHLCSåŸºå› çªå˜è‡´å ¨ç¾§åŒ–é ¶åˆæˆé ¶ç¼ºä¹ç—‡.

A boy, aged 16 months, attended the hospital due to head and facial erythema for 15 months and vulva erythema for 10 months with aggravation for 5 days. The boy developed perioral and periocular erythema in the neonatal period and had erythema and papules with desquamation and erosion in the neck, armpit, and trigone of vulva in infancy. Blood gas analysis showed metabolic acidosis; the analysis of amino acid and acylcarnitine profiles for inherited metabolic diseases and the analysis of organic acid in urine suggested multiple carboxylase deficiency; genetic testing showed a homozygous mutation of c.1522C>T(p.R508W) in the HLCS gene. Finally the boy was diagnosed with holocarboxylase synthetase deficiency and achieved a good clinical outcome after oral biotin treatment. This article analyzes the clinical data of a child with holocarboxylase synthetase deficiency and summarizes the etiology, diagnosis, and treatment of this child, so as to provide ideas for clinicians to diagnose this rare disease.

A Rare Biotinidase Deficiency in the Pediatrics Population: Genotype-Phenotype Analysis.

Biotinidase (BTD) deficiency is a rare autosomal recessive metabolic disorder caused by insufficient biotin metabolism, where it cannot recycle the vitamin biotin. When this deficiency is not treated with supplements, it can lead to severe neurological conditions. Approximately 1 in 60,000 newborns are affected by BTD deficiency. The BTD deficiency causes late-onset biotin-responsive multiple carboxylase deficiency, which leads to acidosis or lactic acidosis, hypoglycemia, and abnormal catabolism. BTD deficiency is of two types based on the amount of BTD Enzyme present in the serum. A wide range of pathogenic mutations in the BTD gene are reported worldwide. Mutations in the BTD gene lead to profound and partial BTD deficiency. Profound BTD deficiency results in a severe pathogenic condition. A high frequency of newborns are affected with the partial deficiency worldwide. They are mostly asymptomatic, but symptoms may appear during stressful conditions such as fasting or viral infections. Several pathogenic mutations are significantly associated with neurological, ophthalmological, and skin problems along with several other clinical features. This review discusses the BTD gene mutation in multiple populations detected with phenotypic features. The molecular-based biomarker screening is necessary for the disease during pregnancy, as it could be helpful for the early identification of BTD deficiency, providing a better treatment strategy. Moreover, implementing newborn screening for the BTD deficiency helps patients prevent several diseases.

Biotinidase activity is affected by both seasonal temperature and filter collection cards.

This study set out to examine pre-analytical factors affecting the frequency of positive results in newborn screening for biotinidase deficiency. This investigation was prompted by an increase in the annual screen positive rate for biotinidase deficiency in Ontario from 2.65x10-4 in 2016 to 6.57x10-4 in 2017. Season and trend decomposition was used to separate seasonality from an underlying trend in the time series of biotindase activity measurements for the period 2014-01-12 to 2019-07-27 (n = 798,770). This analysis revealed a marked seasonal effect (winter = median + ⩽ 17 MRU, summer = mean - ⩽20 MRU) and a non-linear negative trend. Seasonal temperature was correlated with biotinidase results (Pearson's r = 0.79) but not with the observed negative trend (Pearson's r = 0.0025). Time series analysis of biotinidase results grouped by print lot of filter paper revealed that recently printed filter paper cards inhibit biotinidase and that this inhibition resolved over time. This study demonstrates that biotindase activity is inhibited by both increased seasonal temperature and collection on newly printed filter cards.

Holocarboxylase synthetase deficiency induced by HLCS gene mutations: a rare disease study / 中国当代儿科杂志

A boy, aged 16 months, attended the hospital due to head and facial erythema for 15 months and vulva erythema for 10 months with aggravation for 5 days. The boy developed perioral and periocular erythema in the neonatal period and had erythema and papules with desquamation and erosion in the neck, armpit, and trigone of vulva in infancy. Blood gas analysis showed metabolic acidosis; the analysis of amino acid and acylcarnitine profiles for inherited metabolic diseases and the analysis of organic acid in urine suggested multiple carboxylase deficiency; genetic testing showed a homozygous mutation of c.1522C>T(p.R508W) in the HLCS gene. Finally the boy was diagnosed with holocarboxylase synthetase deficiency and achieved a good clinical outcome after oral biotin treatment. This article analyzes the clinical data of a child with holocarboxylase synthetase deficiency and summarizes the etiology, diagnosis, and treatment of this child, so as to provide ideas for clinicians to diagnose this rare disease.

Evaluation of patients diagnosed with phenylketonuria and biotinidase deficiency by the newborn screening program: a ten-year retrospective study.

BACKGROUND: Phenylketonuria (PKU) and biotinidase deficiency (BD) are autosomal recessive diseases. If they are not identified and treated early, severe intellectual disability and developmental delay occur. This study was conducted to calculate the ten-year incidence of PKU and BD in the Diyarbakir province of Turkey. METHODS: This cross-sectional study included patients born between 2011-2020 and diagnosed with PKU and BD. Patients with a clear diagnosis had their records evaluated retrospectively. RESULTS: Between 2011 and 2020, blood was taken from 417,525 newborns` heels in Diyarbakir province. As a result of further diagnostic testing, 53 PKU (Incidence: 1:7878) and 177 BD (Incidence: 1:2359) were detected. Of the patients with BD, 56% had profound BD and 44% had partial BD. The records of a total of 269 patients (PKU: 25; BD: 123; Hyperphenylalaninemia: 121) were examined. Parents of 65% (n=15) of the patients diagnosed with PKU and 46.6% (n=55) of the patients diagnosed with BD were consanguineous. CONCLUSIONS: The incidence of both PKU and BD was found to be high in our region. The high number of consanguineous marriages was regarded as the most important explanation for the high frequency of these illnesses.

A Treatable Cause of Myelopathy: Biotinidase Deficiency Presenting as Acute Flaccid Paralysis.

Biotinidase deficiency (BD) is a rare treatable cause of neurometabolic disorders. It is an autosomal recessive disorder that manifests with cutaneous and neurological manifestations. Spinal cord involvement is uncommon with only a few cases reported in the literature. A 6-year-old female child presented with progressive difficulty in walking since 2 months. At 6 months of age, the child was elsewhere evaluated for global developmental delay and suspected as metabolic disorders and started on megavitamins, following which the child was improved. For the past 2 years, she has stopped medicines. On examination, irritable, alopecia, eczema, hypotonia, and power of two-fifths in all four limbs, and exaggerated deep tendon reflexes. The magnetic resonance imaging (MRI) brain and spine showed T2/fluid-attenuated inversion recovery (FLAIR) hyperintensities in periaqueductal gray matter, dorsal midbrain, pons, medulla, and cervical cord. She was suspected to have BD and confirmed by low enzyme levels and pathogenic variant in BTD . She was started on biotin supplements that resulted clinically dramatic improvement and MRI became normal within 4 weeks. Any child presenting with acute flaccid paralysis with brainstem and spinal cord noncompressive lesions on MRI, rare treatable conditions like BD should be considered in developing countries, like India, where still no universal newborn screening facilities are available.

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

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.

Revisiting the administration of biotin to children with biotin-responsive disorders.

There continues to be questions and misconceptions about the administration of the vitamin, biotin, to children with the inherited biotin-responsive disorder, especially infants. Therefore, this commentary is intended to address the issues of biotin administration for healthcare workers, parents of children with the biotin-responsive disorders and the individuals with the disorders.

Molecular Background and Disease Prevalence of Biotinidase Deficiency in a Polish Population-Data Based on the National Newborn Screening Programme.

Biotinidase deficiency (BD) is a rare autosomal recessive metabolic disease. Previously the disease was identified only by clinical signs and symptoms, and since recently, it has been included in newborn screening programs (NBS) worldwide, though not commonly. In Europe, BD prevalence varies highly among different countries, e.g., from 1:7 116 in Turkey to 1:75 842 in Switzerland. This paper aimed to present the molecular spectrum of BD (profound and partial forms) in Polish patients diagnosed within the national NBS of 1,071,463 newborns. The initial suspicion of BD was based on an abnormal biotinidase activity result determined in a dry blood spot (DBS) by colorimetric and by fluorimetric methods while biochemical verification was determined by serum biotinidase activity (as quantitative analysis). The final diagnosis of BD was established by serum enzyme activity and the BTD gene direct sequencing. The obtained results allowed for the estimation of disease prevalence (1:66,966 births, while 1:178,577 for profound and 1:107,146 for partial forms), and gave novel data on the molecular etiology of BD.