High frequency of biotinidase deficiency in Italian population identified by newborn screening

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.

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.

Expanded Newborn Screening in Italy Using Tandem Mass Spectrometry: Two Years of National Experience

Newborn screening (NBS) for inborn errors of metabolism is one of the most advanced tools for secondary prevention in medicine, as it allows early diagnosis and prompt treatment initiation. The expanded newborn screening was introduced in Italy between 2016 and 2017 (Law 167/2016; DM 13 October 2016; DPCM 12-1-2017). A total of 1,586,578 infants born in Italy were screened between January 2017 and December 2020. For this survey, we collected data from 15 Italian screening laboratories, focusing on the metabolic disorders identified by tandem mass spectrometry (MS/MS) based analysis between January 2019 and December 2020. Aminoacidemias were the most common inborn errors in Italy, and an equal percentage was observed in detecting organic acidemias and mitochondrial fatty acids beta-oxidation defects. Second-tier tests are widely used in most laboratories to reduce false positives. For example, second-tier tests for methylmalonic acid and homocysteine considerably improved the screening of CblC without increasing unnecessary recalls. Finally, the newborn screening allowed us to identify conditions that are mainly secondary to a maternal deficiency. We describe the goals reached since the introduction of the screening in Italy by exchanging knowledge and experiences among the laboratories.

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.

Late Onset Subacute Profound Biotinidase Deficiency Caused by a Novel Homozygous Variant c.466-3T>G in the BTD Gene

Biotinidase deficiency (BD) is an autosomal recessive disorder caused by bi-allelic mutation in the BTD gene. Clinical manifestations in BD mainly depends on residual biotinidase enzyme activity, although there are some exceptions. Broadly BD disorders are classified as profound BD and partial BD. Further profound BD can be early onset, late onset, and sometimes may be asymptomatic. Clinically late-onset profound BD can present with spectrum of manifestations ranging from single organ to multiple organ involvement, typically affecting function of brain, eye, ear, and skin. Here, a first-born child to consanguineous parents with late-onset profound BD presenting with hyperventilation secondary to lactic acidosis, hypotonia, evolving spasticity, and abnormal neuroimaging findings caused by novel homozygous variant, c.466-3T>G in the BTD gene is reported.

Expert consensus on screening, diagnosis and treatment of multiple carboxylase deficiency

Multiple carboxylase deficiency (MCD) includes autosomal recessive holocarboxylase synthetase (HLCS) deficiency and biotinidase (BTD) deficiency, which are caused by and gene mutations respectively. Neonatal screening for HLCS deficiency is based on 3-hydroxyisovaleryl carnitine in dry blood filter paper, and BTD deficiency is based on BTD activity determination. HLCS deficiency and BTD deficiency are characterized by neurocutaneous syndrome and organic aciduria, however, they are different in onset age, neurological symptoms and metabolic decompensation, which needed to be differentiated from acquired biotin deficiency or other genetic metabolic diseases. The diagnosis of the disease requires a combination of biochemical characteristics of hematuria, enzyme activity determination and genetic test. Routine biotin doses are effective for most MCD patients. This consensus is intended to benefit early screening and diagnosis of MCD.

Partial Biotinidase Deficiency Revealed Imbalances in Acylcarnitines Profile at Tandem Mass Spectrometry Newborn Screening

Biotinidase (BTD) deficiency is an autosomal recessive inherited neurocutaneous disorder. BTD recycles the vitamin biotin, a coenzyme essential for the function of four biotin-dependent carboxylases, including propionyl-CoA carboxylase, 3-methylcrotonyl-CoA carboxylase, pyruvate carboxylase, and acetyl-CoA carboxylase. Due to deficient activities of the carboxylases, BTD deficiency is also recognized as late-onset multiple carboxylase deficiency and is associated with secondary alterations in the metabolism of amino acids, carbohydrates, and fatty acids. BTD deficiency can be classified as "profound", with less than 10% of mean normal activity, and as "partial" with 10-30% of mean normal activity. Newborn screening (NBS) of BTD deficiency is performed in most countries and is able to detect both variants. Moreover, mild metabolic alterations related to carboxylase deficiency in profound BTD deficiency could result and possibly be revealed in the metabolic profile by tandem mass spectrometry (MS/MS) NBS. Here, we report the case of a newborn female infant with an initial suspected BTD deficiency at the NBS test, finally confirmed as a partial variant by molecular testing. Although BTD deficiency was partial, interestingly her metabolic profile at birth and during the follow-up tests revealed, for the first time, alterations in specific acylcarnitines as a possible result of the deficient activity of biotin-dependent carboxylases.

Newborn Screening for Biotinidase Deficiency. The Experience of a Regional Center in Italy

Introduction: Biotinidase deficiency (BD) is an autosomal recessive disease causing a defect in the biotin-releasing enzyme. Newborn screening (NBS) allows early diagnosis and treatment, ensuring excellent prognosis. The aim of this study was to describe our experience in the diagnosis, treatment, and follow-up showing key strategies and unsolved questions of the management of BD patients. Methods: We analyzed data of patients identified by the Regional Centre for Newborn Screening of Verona and followed by the Inherited Metabolic Disease Unit of Verona and Neonatal Intensive Care Unit of Bolzano, Italy, from 2014 to 2020. Results: Thirty-seven patients were diagnosed by NBS (five profound and 32 partial BD), with a total incidence of 1:5,996. All were started on biotin at diagnosis and presented no symptoms at follow-up. Analysis of parents and siblings led to identification of five asymptomatic patients with partial BD: one asymptomatic parent and four young siblings. Genetic analysis of the BTD gene identified 17 different genotypes and one mutation not previously known. Discussion: Our data confirm that NBS introduction had a dramatic impact on BD diagnosis, and the incidence has increased significantly compared to other areas. Partial defects are more common than profound and have a distinctive genotype. Partial BD treatment is still controversial even at what dose of biotin and for how long. At the end, BD treatment is very easy and inexpensive and prevents severe neurological damage. Sharing experiences is essential to achieving guidelines for treatment and follow-up and a better genotype-phenotype correlation.