Sequence variants in the BTD underlying biotinidase deficiency in families of Pakistani origin.

BACKGROUND: Biotinidase deficiency (BTD) is a rare autosomal recessive metabolic disease, which develops neurological symptoms because of the impaired biotin recycling. Pathogenic mutations on BTD gene cause BTD deficiency. The clinical features and mutation analysis of Pakistani children with BTD deficiency have rarely been described. Herein, for the first time, we report the clinical features, BTD gene mutations and biochemical analysis of seven symptomatic children with BTD deficiency from Pakistan. METHODS: Seven suspected BTD-deficient patients who presented abnormal organic acid profiles and clinical features were subjected to Sanger sequencing to identify pathogenic mutations in the BTD gene. The results were analyzed by Mutation Surveyor Software. RESULTS: All seven patients exhibited common biotinidase deficiency symptoms including hypotonia, developmental delay and seizures. Biochemical analysis shows marked excretion of 3-hydroxy isovalerate in all cases, followed by 3-hydroxy propionate and methyl citrate. Sanger sequencing revealed one frame-shift mutation, c.98_104delinsTCC (p.Cys33Phefs), and two missense mutations, c.1612C>A (p.Arg538Ser) and c.1330G>C (p.Asp444His). All mutations were in the homozygous state and classified as pathogenic in published studies and mutation databases. CONCLUSIONS: This study has validated the BTD variants as the underlying cause of biotinidase deficiency in which molecular testing of BTD is supported by urinary organic acid analysis and clinical diagnosis. Secondly, the strength of the local availability of this test in Pakistan will paved the way for the neonatal screening of biotinidase deficiency.

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.

Two novel BTD mutations causing profound biotinidase deficiency in a Chinese patient.

BACKGROUND: Biotinidase deficiency (OMIM 253260) is an autosomal recessively inherited disorder affecting about 1/60,000 people worldwide. The absence or deficiency of biotinidase impairs free biotin recycling and affects biotin-dependent carboxylase functions. METHODS: A Chinese patient with spontaneous recurrent epilepsy, an eczema-like rash, hair loss, hypotonia, and hearing loss began at three months of age. Her biotinidase activity was 1.0 nmol/ml/min, 9.5% of the mean control activity, which confirmed profound biotinidase deficiency. RESULTS: Compound heterozygous for c.250-1G > C and c.878dupT variants in the BTD gene were identified in this patient. These two variants were novel and absent in the population matched controls and any databases. CONCLUSIONS: This study expanded the mutation spectrum of alterations of the BTD gene. Our patient also emphasized the critical role of biotinidase activity measurement combined with mutation analysis in early diagnosis of biotinidase deficiency.

Biotin: overview of the treatment of diseases of cutaneous appendages and of hyperseborrhea.

One of the most common micronutrient deficiencies with cutaneous findings is the vitamin B, also known as biotin, deficiency. Biotin deficiency may be due to congenital lack of biotinidase, or acquired following some conditions that interfere with its absorption, such as inflammatory bowel disorders, a diet too rich in avidin, magnesium deficiency, smoking habit and treatment with broad-spectrum antibiotics, anticonvulsants and sulfonamides. This review highlights the role of biotin in the most common skin disorders such associated with biotin deficiency and an approach to their treatment. Biotin administration may improve the treatment of hair loss when deficiency is detected on the basis of a careful patient history, clinical examination and the determination of serum biotin levels. The use of biotin is rationale in seborrheic dermatitis as the vitamin intercepts the main metabolic pathways underlying the pathogenesis of the disease. Treatment with biotin could also be useful in comedonal acne characterized by a high rate of seborrhea, and may be helpful for acne treated with topical retinoids, contributing to the control of flaking and irritation. The tolerability of biotin is excellent and there is no risk of hypervitaminosis even in the case of high doses. It is important that administration is controlled by physicians and follows a medical diagnosis and prescription. Correct doses used in dermatological conditions are safe and are not at risk of interference with laboratory tests.

Genotypic and phenotypic correlations of biotinidase deficiency in the Chinese population.

Biotinidase deficiency is an autosomal recessive disorder that affects the endogenous recycling and release of biotin from dietary protein. This disease was thought to be rare in East Asia. In this report, we delineate the phenotype of biotinidase deficiency in our cohort. The genotypes and phenotypes of patients diagnosed with biotinidase deficiency from a medical center were reviewed. The clinical manifestations, laboratory findings, and molecular test results were retrospectively analyzed. A total of 6 patients were evaluated. Three patients (50%) were diagnosed because of a clinical illness, and the other three (50%) were identified by newborn screening. In all patients, the molecular results confirmed the BTD mutation. The three patients with clinical manifestations had an onset of seizure at the age of 2 to 3 months. Two patients had respiratory problems (one with apnea under bilevel positive airway pressure (BiPAP) therapy at night, and the other with laryngomalacia). Hearing loss and eye problems were found in one patient. Interestingly, cutaneous manifestations including skin eczema, alopecia, and recurrent fungal infection were less commonly seen compared to cases in the literature. None of the patients identified by the newborn screening program developed symptoms. Our findings highlight differences in the genotype and phenotype compared with those in Western countries. Patients with biotinidase deficiency benefit from newborn screening programs for early detection and management.

Developmental window of sensorineural deafness in biotinidase-deficient mice.

Biotinidase deficiency is an autosomal recessively inherited disorder that results in the inability to recycle the vitamin, biotin. If untreated, the disorder can result in a range of neurological and cutaneous symptoms, including sensorineural deficits and deafness. To understand early mechanistic abnormalities that may precede more generalized and nonspecific effects of metabolic deficits such as weight loss and acidosis, we have analyzed auditory brainstem responses (ABRs) in biotinidase-deficient knockout (Btd -/- ) mice in the periweaning period with or without dietary biotin supplementation. We find significant increases in the latency of wave V of the ABR elicited by pure tone stimuli at one octave intervals, which precede substantial increases in ABR thresholds. Finer interpeak latency analyses of these changes indicate they are confined to the latter ABR waves associated with the CNS and likely reflect slowed brainstem transmission time. In contrast, peripheral nervous system conduction velocity appears normal. Further, we find that biotin-supplementation after the onset of symptoms reverses the latency shifts, which has significant relevance for early treatment in patients. Finally, ABR latencies in Btd -/- mice fed a biotin-supplemented diet for the first month of life appear refractory to transmission time slowing during a subsequent bout of biotin deficiency. These data suggest a transient vulnerability window for biotin deficiency in the auditory brainstem. Finally, we also observe a developmental vulnerability window involving follicular melanosome production or melanocyte survival. Sensorineural deafness precedes peripheral hearing loss in developmental biotinidase deficiency and is transient if rescued by dietary biotin within a short developmental window.

Biotinidase deficiency: Genotype-biochemical phenotype association in Brazilian patients.

INTRODUCTION: The association between the BTD genotype and biochemical phenotype [profound biotinidase deficiency (BD), partial BD or heterozygous activity] is not always consistent. This study aimed to investigate the genotype-biochemical phenotype association in patients with low biotinidase activity. METHODS: All exons, the 5'UTR and the promoter of the BTD gene were sequenced in 72 Brazilian individuals who exhibited low biotinidase activity. For each patient, the expected biochemical phenotype based on the known genotype was compared with the observed biochemical phenotype. Additional non-genetic factors that could affect the biotinidase activity were also analysed. RESULTS: Most individuals were identified by neonatal screening (n = 66/72). When consecutive results for the same patient were compared, age, prematurity and neonatal jaundice appeared to affect the level of biotinidase activity. The biochemical phenotype at the time of the second blood collection changed in 11/22 patients compared to results from the first sample. Three novel variants were found: c.1337T>C (p.L446P), c.1466A>G (p.N489S) and c.962G>A (p.W321*). Some patients with the same genotype presented different biochemical phenotypes. The expected and observed biochemical phenotypes agreed in 68.5% of cases (concordant patients). The non-coding variants c.-183G>A, c.-315A>G and c.-514C>T were present in heterozygosis in 5/17 discordant patients. In addition, c.-183G>A and c.-514C>T were also present in 10/37 concordant patients. CONCLUSIONS: The variants found in the promoter region do not appear to have a strong impact on biotinidase activity. Since there is a disparity between the BTD genotype and biochemical phenotype, and biotinidase activity may be affected by both genetic and non-genetic factors, we suggest that the diagnosis of BD should be based on more than one measurement of plasma biotinidase activity. DNA analysis can be of additional relevance to differentiate between partial BD and heterozygosity.

Biotin deficiency enhances the inflammatory response of human dendritic cells.

The water-soluble biotin (vitamin B7) is indispensable for normal human health. The vitamin acts as a cofactor for five carboxylases that are critical for fatty acid, glucose, and amino acid metabolism. Biotin deficiency is associated with various diseases, and mice deficient in this vitamin display enhanced inflammation. Previous studies have shown that biotin affects the functions of adaptive immune T and NK cells, but its effect(s) on innate immune cells is not known. Because of that and because vitamins such as vitamins A and D have a profound effect on dendritic cell (DC) function, we investigated the effect of biotin levels on the functions of human monocyte-derived DCs. Culture of DCs in a biotin-deficient medium (BDM) and subsequent activation with LPS resulted in enhanced secretion of the proinflammatory cytokines TNF-α, IL-12p40, IL-23, and IL-1ß compared with LPS-activated DCs cultured in biotin-sufficient (control) and biotin-oversupplemented media. Furthermore, LPS-activated DCs cultured in BDM displayed a significantly higher induction of IFN-γ and IL-17 indicating Th1/Th17 bias in T cells compared with cells maintained in biotin control or biotin-oversupplemented media. Investigations into the mechanisms suggested that impaired activation of AMP kinase in DCs cultured in BDM may be responsible for the observed increase in inflammatory responses. In summary, these results demonstrate for the first time that biotin deficiency enhances the inflammatory responses of DCs. This may therefore be one of the mechanism(s) that mediates the observed inflammation that occurs in biotin deficiency.

Biotinidase deficiency due to a de novo mutation or gonadal mosaicism in a first child.

Biotinidase deficiency (BD), which is caused by BTD genetic lesions, if untreated, can result in neurological and cutaneous manifestations. Biotin supplementation can improve or prevent symptoms. We herewith present a family, which we studied at biochemical and molecular level, after identifying the proband through a newborn screening programme. BTD gene molecular analysis showed the proband to be compound heterozygous for the c.1330G>C p.(Asp444His) mild known variant, and for the c.1475 C>T p.(Thr492Ile) new variant. Bioinformatic analysis allowed us to confirm the pathogenic role of the newly identified variant. The proband's father, who exhibited low biotinidase (BTD) enzyme activity, was homozygous for the mild variant, whereas the proband's mother, who exhibited borderline BTD values, the BTD mutation carrier status could not be detected. This is the first description of a patient with BD harbouring a variant whose origin is either de novo or the consequence of gonadal mosaicism. BTD molecular analysis and bioinformatic tools for the evaluation of pathogenicity of newly identified variants are necessary for diagnostic purposes (i.e., clarifying borderline enzyme assays and the carrier status of parents), and for genetic counselling.

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

PURPOSE: Biotinidase 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. METHODS: We 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. RESULTS: Individuals 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. CONCLUSION: Individuals 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.Genet Med 17 3, 205-209.

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

BACKGROUND: Biotinidase 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. METHODS: This observational, multicenter study used a convenience sampling strategy, with sequencing of exons 2, 3, and 4 of the BTD gene. RESULTS: The 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%). CONCLUSIONS: Our 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.

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.

Consumption of a low-carbohydrate and high-fat diet (the ketogenic diet) exaggerates biotin deficiency in mice.

OBJECTIVE: Biotin is a water-soluble vitamin that acts as a cofactor for several carboxylases. The ketogenic diet, a low-carbohydrate, high-fat diet, is used to treat drug-resistant epilepsy and promote weight loss. In Japan, the infant version of the ketogenic diet is known as the "ketone formula." However, as the special infant formulas used in Japan, including the ketone formula, do not contain sufficient amounts of biotin, biotin deficiency can develop in infants who consume the ketone formula. Therefore, the aim of this study was to evaluate the effects of the ketogenic diet on biotin status in mice. METHODS: Male mice (N = 32) were divided into the following groups: control diet group, biotin-deficient (BD) diet group, ketogenic control diet group, and ketogenic biotin-deficient (KBD) diet group. Eight mice were used in each group. RESULTS: At 9 wk, the typical symptoms of biotin deficiency such as hair loss and dermatitis had only developed in the KBD diet group. The total protein expression level of biotin-dependent carboxylases and the total tissue biotin content were significantly decreased in the KBD and BD diet groups. However, these changes were more severe in the KBD diet group. CONCLUSION: These findings demonstrated that the ketogenic diet increases biotin bioavailability and consumption, and hence, promotes energy production by gluconeogenesis and branched-chain amino acid metabolism, which results in exaggerated biotin deficiency in biotin-deficient mice. Therefore, biotin supplementation is important for mice that consume the ketogenic diet. It is suggested that individuals that consume the ketogenic diet have an increased biotin requirement.

Temporal development of genetic and metabolic effects of biotin deprivation. A search for the optimum time to study a vitamin deficiency.

Biotin deficiency (Bt-D) is usually studied at the point at which the animal model exhibits the signs of full-blown deficiency symptoms; in rats, this typically occurs at 6-8 weeks of feeding a deficient diet. To differentiate specific deficiency effects from those of undernutrition, biotin sufficient and deficient rats were studied at 2, 3, 4, and 5 weeks on the deficiency diet, before the onset of weight loss and deficiency signs. The deficiency state was confirmed by biochemical and molecular analyses. Blood and liver metabolites were determined and western blots of signaling proteins, and qRT-PCR gene expression studies. The main effects of Bt-D were already well established by the fourth week on the diet; thus, we consider the fourth week as the optimum time to study the consequences of biotin depletion. Early effects, which were already apparent at week 2, included cellular energy deficit (as assessed by increased AMP/ATP ratio), activation of the AMPK energy sensor, and changes of carbon metabolism gene transcripts (e.g., phosphoenolpyruvate carboxykinase, carnitine palmitoyl transferase 1, liver glucokinase and fatty acid synthetase). Reduced post-prandial blood concentrations of glucose were also observed early; we speculate that these are attributable to augmented sensitivity to insulin and increased glucose utilization, a likely effect of AMPK induction of translocation of glucose transporter GLUT4 to the cell membranes and increased hexokinase expression. Other late-onset changes (week 4) included increased serum concentrations of lactate and free fatty acids and decreased liver glycogen and serum concentrations of triglycerides and total cholesterol. The identification of the early specific molecular and metabolic disturbances of biotin deficiency might be useful in identifying individuals with marginal deficiency of this vitamin, which appears to be common in normal human pregnancy. The study of time-course of other vitamin deficiencies, such as this one, might help to better understand and cope with their effects.

Biotinidase deficiency presenting as recurrent myelopathy in a 7-year-old boy and a review of the literature.

Biotinidase deficiency may produce variable neurologic manifestations. Brainstem and spinal cord disease comprises an uncommon presentation of biotinidase deficiency. We describe a 7-year old boy with subacute progressive quadriplegia and "sighing" respirations. Severe biotinidase deficiency was established, and the patient demonstrated complete recovery with biotin supplementation. Genetic studies revealed presence of homozygous mutation in the BTD gene [c.133C>T (p.H447Y)]. Biotinidase deficiency should be considered in the differential diagnosis for subacute, long segment myelopathy, particularly with brainstem involvement. This entity is treatable; a high index of suspicion can be life-saving. We also review the literature on biotinidase deficiency presenting as spinal cord demyelinating disease.

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.

Analysis of mutations causing biotinidase deficiency.

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.

Spinal cord demyelination associated with biotinidase deficiency in 3 Chinese patients.

Biotinidase deficiency is a treatable cause of severe neurological disorders and skin problems. Spinal cord impairment is a rare complication of this disease and is commonly unrecognized. The authors encountered 3 Chinese patients with progressive spinal cord demyelination associated with biotinidase deficiency. Case 1 exhibited fatigue, proximal muscular weakness, and hypotonic paraplegia from the age of 7 years 4 months. Demyelination of cervical and thoracic cord was evident on magnetic resonance imaging (MRI). Case 2 developed visual impairment, blepharoconjunctivitis, and optic nerve atrophy from 5 years of age, which combined with progressive hypertonic paralysis, ataxia, and alopecia from the age of 7 years. His spinal MRI T2-weighted sequence revealed an extensive hyperintense lesion involving the cervical spinal cord C(2) to C(4). Bilateral optic nerves were significantly thick. In case 3, intercurrent wheezing, tachypnea, dyspnea, and lethargy occurred from the age of 1 year. Medulla and upper cervical spine edema and demyelination were found on MRI. Markedly elevated urine organic acids and decreased blood biotinidase activities were observed in the 3 patients. Biotin supplementation led to a dramatic improvement of clinical symptoms in 3 patients. The findings indicate that biotinidase deficiency should be considered in the differential diagnosis of unexplained spinal cord demyelination because prompt diagnosis and treatment with biotin may enable an excellent recovery.

Novel mutation causing partial biotinidase deficiency in a Syrian boy with infantile spasms and retardation.

We report a case of partial biotinidase deficiency (plasma biotinidase levels: 1.30 nm/minute/mL) in a 7-month-old boy who presented with evidence of perinatal distress followed by developmental delay, hypotonia, seizures, and infantile spasms without alopecia or dermatitis. His neurologic symptoms improved markedly on biotin supplementation and antiepileptic drug therapy. DNA mutational analysis revealed that the patient was homozygous for a novel E64K mutation and his parents were heterozygous for the same mutation. Whereas preexisting perinatal distress probably contributed to the severity of the patient's symptoms, the described mutation is novel and is possibly responsible for at least some of his clinical manifestations.