Clinical features, BTD gene mutations, and their functional studies of eight symptomatic patients with biotinidase deficiency from Southern China

Identification of the mutations in BTD gene in Iranian patients with biotinidase deficiency and evaluating their genotype-phenotype correlations

BACKGROUND

Biotinidase (BTD, encoded by the BTD gene) deficiency is an autosomal recessive neurometabolic disease caused by abnormal BTD activity in the biotin cycle. The clinical symptoms of patients, which are mainly neurocutaneous, range from mild to severe based on the enzyme activity level. This study aimed to identify BTD gene mutations in suspected BTD deficiency patients for the first time in the southwest of Iran and evaluate their genotype-phenotype correlations.

METHODS

11 clinically and biochemically suspected patients from nine unrelated families and their available family members were subjected to Sanger sequencing. Segregation analysis was performed for novel mutation. The effect of each mutation on protein stability and hydropathicity, as well as the pathogenicity prediction of all detected mutations were assessed using various in silico analysis tools.

RESULTS

Six mutations including a novel and five previously reported mutations were identified in patients with different ethnicities. Three out of five known mutations were reported for the first time in Iran. Various common clinical manifestations and a rarely reported coexistence of celiac disease in biotinidase deficiency patients were observed. The novel missense variant c.787G > A (p.Glu263Lys) was detected in exon 4 of the BTD gene, within the biotinidase-like domain of the BTD protein. This variation was found in two cousins of a family, both developed the same initial clinical presentation. In silico analyses revealed that this missense substitution decreased protein stability and increased protein hydrophilicity. Additionally, the known frameshift mutation c.1264delG (p.val422serfster59), was the most frequent allele in the studied population. We also predicted and visualized the effects of the novel and frameshift mutations on protein structure.

CONCLUSION

Our findings expanded the mutational spectrum of the BTD gene and provided valuable data on genotype-phenotype correlations, which helps in genetic counseling. Furthermore, the necessity of performing molecular analysis along with enzymatic analysis was highlighted by this study.

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.

Structural, rheological, and gelling characteristics of starch-based materials in context to 3D food printing applications in precision nutrition

Starch-based materials have viscoelasticity, viscous film-forming, dough pseudoplasticity, and rheological properties, which possess the structural characteristics (crystal structure, double helix structure, and layered structure) suitable for three-dimensional (3D) food printing inks. 3D food printing technology has significant advantages in customizing personalized and precise nutrition, expanding the range of ingredients, designing unique food appearances, and simplifying the food supply chain. Precision nutrition aims to consider individual nutritional needs and individual differences, which include special food product design and personalized precise nutrition, thus expanding future food resources, then simplifying the food supply chain, and attracting extensive attention in food industry. Different types of starch-based materials with different structures and rheological properties meet different 3D food printing technology requirements. Starch-based materials suitable for 3D food printing technology can accurately deliver and release active substances or drugs. These active substances or drugs have certain regulatory effects on the gut microbiome and diabetes, so as to maintain personalized and accurate nutrition.

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.

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.

Whole-Exome Sequencing Reveals a Missense Variant c.1612C>T (p.Arg538Cys) in the BTD Gene Leading to Neuromyelitis Optica Spectrum Disorder in Saudi Families

Biotinidase deficiency is an autosomal recessive, multiple carboxylase deficiency usually associated with seizures, eczema, hypotonia, visual disturbances, hearing loss, and developmental delays. Only a handful of cases of biotinidase deficiency that had clinical features of neuromyelitis optica spectrum disorder have been reported in the literature. The case report study is about the clinical and genetic features of two pediatric patients from different families with biotinidase deficiency whose brain and spine MRI scans were suggestive of neuromyelitis optica. Neither child improved with immunotherapy. They come from a first-degree blood-related family. In both cases, a deficiency of the enzyme biotinidase was detected. The missense variant NM_001370658.1 (BTD):c.1612C>T (p.Arg538Cys) NM_000060.4 in exon 4 was identified by whole-exome sequencing. The identified sequence variation was validated using Sanger sequencing analysis. The intake of biotin resulted in clinical improvement. After a follow-up period of 12 months, the patient was gradually weaned from tracheostomy. His vision had improved significantly. He was able to walk and run independently. In conclusion, biotinidase deficiency is a rare and treatable cause of neuromyelitis optica. Early diagnosis can prevent poor clinical outcomes. Biotinidase enzyme levels should be considered as part of the examination algorithm for neuromyelitis optica spectrum disorder.

Clinical, biochemical and mutational findings in biotinidase deficiency among Malaysian population

Introduction

Biotinidase deficiency (BD) is an autosomal recessively inherited disorder characterized by developmental delay, seizures, hypotonia, ataxia, skin rash/eczema, alopecia, conjunctivitis/visual problem/optic atrophy and metabolic acidosis. Delayed diagnosis may lead to irreversible neurological damage.

Methodology

Clinically suspected patients were screened for biotinidase level by a fluorometry method. Profound BD patients were confirmed by mutation analysis of BTD gene.

Results

9 patients had biotinidase activity of less than 77 U. 3 patients (33%) had profound BD while 6 patients (67%) had partial BD. Compound heterozygous mutations were detected at c.98_104delinsTCC p.(Cys33Phefs*36) in Exon 2 and c.833T>C p.(Leu278Pro) in Exon 4 in two patients and a homozygous mutation at c.98_104delinsTCC p.(Cys33Phefs*36) in Exon 2 in another patient.

Conclusion

Correct diagnosis lead to early treatment and accurate management of patient. Biochemical screening of BD in symptomatic child is prerequisite to determine enzyme status however molecular confirmation is vital in differentiating individuals with profound biotinidase deficiency from partial biotinidase deficiency and also individuals' carriers.

The novel homozygous p.Asn197_Ser201del mutation in BTD gene is associated with profound biotinidase deficiency in an Iranian consanguineous family

BACKGROUND

Biotinidase deficiency is an autosomal recessive inherited inborn error of biotin metabolism. Biotin as a water-soluble vitamin is the prosthetic group of biotin-dependent carboxylase enzymes, and by enhancing their function plays a key role in amino acid catabolism, fatty acid synthesis, and gluconeogenesis. Beyond its prosthetic group role, it has been recognized that biotin regulates the level of gene transcription in the eukaryotic cells, therefore any defect in these pathways causes a multisystem metabolic disorder characterized by neurological and cutaneous symptoms.

METHODS AND RESULTS

We report the identification of a novel pathogenic variant in the BTD gene, c.528_542del15 (p.Asn197_Ser201del, UniProt P43251-1) in an Iranian consanguineous family with a severe form of the disease. The segregation analysis in the family was consistent with phenotype and the identified variant was predicated as a pathogenic mutation by the in-silico prediction tools. Computer structural modeling suggests the deleted amino acid residues are located near the biotinidase active site and disrupt the special conformations which are critical for the enzyme activity, and also N-glycosylation.

CONCLUSIONS

This study further expands the mutation spectrum of the BTD gene underlying cause of profound biotinidase deficiency.

Identification and Characterization of BTD Gene Mutations in Jordanian Children with Biotinidase Deficiency

Biotinidase deficiency is an autosomal recessive metabolic disorder whose diagnosis currently depends on clinical symptoms and a biotinidase enzyme assay. This study aimed to investigate the mutational status and enzymatic activity of biotinidase deficiency in seven unrelated Jordanian families including 10 patients and 17 healthy family members. Amplified DNA was analyzed by the automated Sanger sequencing method, and the enzymatic assay was performed using a colorimetric assessment. Biotinidase level was significantly lower (p < 0.001) in BTD children compare to their non-affected family members. Genetic sequencing revealed six different mutations in Jordanian patients. One mutation was novel and located in exon 4, which could be a prevalent mutation for biotinidase deficiency in the Jordanian population. Identification of these common mutations and combing the enzymatic activity with genotypic data will help clinicians with regard to better genetic counseling and management through implementing prevention programs in the future.

Effect of BTD gene variants on in vitro biotinidase activity

INTRODUCTION

Biotinidase deficiency (BD), an autosomal recessive disease, is classified into profound (activity <10%) or partial BD (activity 10-30%). The most frequent variant in patients worldwide is c.1330G > C (p.Asp444His), which is associated with partial BD. In vivo studies indicate that this variant reduces the biotinidase activity by 50%. The objective of this study was to evaluate the in vitro effect of p.Asp444His and of five novel variants identified among Brazilian individuals showing low activity of biotinidase in serum.

METHODS

The variants c.119 T > C (p.Leu40Pro), c.479G > A (p.Cys160Tyr), c.664G > A (p.Asp222Asn), c.1330G > C (p.Asp444His), c.1337 T > C (p.Leu446Pro), c.1466A > G (p.Asn489Ser) and the wild type (wt) BTD gene were expressed in HEK 293 cells. Biotinidase activity was quantified by colorimetric method in cells homogenates and culture medium. The wtBTD activity was considered 100%.

RESULTS

The p.Leu40Pro, p.Cys160Tyr and p.Leu446Pro variants were associated to impaired biotinidase activity (activity in cells: 33%, 14%, 0%, respectively; activity in medium: 7%, 0.3%, 2%, respectively) and undetectable amount of protein in intra and extracellular space. The p.Asn489Ser variant had these effects restricted to the extracellular space (activity in medium: 43%), and the p.Asp222Asn variant showed normal activity. The expression of p.Asp444His variant resulted in detectable protein and slightly reduced activity only in cells (activity in cells: 46%; activity in medium: 115%).

CONCLUSION

Our findings suggest that the p.Leu40Pro, p.Cys160Tyr and p.Leu446Pro variants are deleterious; the p.Asn489Ser is probably related to a mild biochemical phenotype; and p.Asp222Asn variant is probably not deleterious. The p.Asp444His variant seems to code for a protein with variable activity.

Single center experience of biotinidase deficiency: 259 patients and six novel mutations

Background Biotinidase deficiency (BD) is an autosomal recessively inherited disorder of biotin recycling. It is classified into two levels based on the biotinidase enzyme activity: partial deficiency (10%-30% enzyme activity) and profound deficiency (0%-10% enzyme activity). The aims of this study were to evaluate our patients with BD, identify the spectrum of biotinidase (BTD) gene mutations in Turkish patients and to determine the clinical and laboratory findings of our patients and their follow-up period. Methods A total of 259 patients who were diagnosed with BD were enrolled in the study. One hundred and forty-eight patients were male (57.1%), and 111 patients were female (42.9%). Results The number of patients detected by newborn screening was 221 (85.3%). By family screening, 31 (12%) patients were diagnosed with BD. Seven patients (2.7%) had different initial complaints and were diagnosed with BD. Partial BD was detected in 186 (71.8%) patients, and the profound deficiency was detected in 73 (28.2%) patients. Most of our patients were asymptomatic. The most commonly found variants were p.D444H, p.R157H, c.98_104delinsTCC. The novel mutations which were detected in this study are p.D401N(c.1201G>A), p.A82G (c.245C>G), p.F128S(c.383T>C), c617_619del/TTG (p.Val207del), p.A287T(c.859G>A), p.S491H(c.1471A>G). The most common mutation was p.R157H in profound BD and p.D444H in partial BD. All diagnosed patients were treated with biotin. Conclusions The diagnosis of BD should be based on plasma biotinidase activity and molecular analysis. We determined the clinical and genetic spectra of a large group of patients with BD from Western Turkey. The frequent mutations in our study were similar to the literature. In this study, six novel mutations were described.