Biotinidase deficiency should be considered in individuals thought to have multiple sclerosis and related disorders

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.

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.

Accurate determination of Biotinidase activity in serum by HPLC and its utilization as second tier test for the confirmation of initial positive newborn screening results

Diagnosis of Biotinidase deficiency (BTD) is extremely important to avoid several neurodevelopmental problems in early childhood. Colorimetric and fluorometric methods lack specificity and selectivity due to several interferences resulting in a high number of false positive results. We developed an HPLC method for BTD activity in serum with fluorescent detection. In colorimetric assays, biotinidase attacks the amide linkage of the artificial substrate biotinidyl-4-aminobenzoic acid (B-PABA) and releases p-aminobenzoic acid (PABA), which is converted to a purple dye by diazotization reaction. The newly developed method injects the reaction mixture directly into the HPLC column and quantifies using a six-point calibration curve without coupling and diazotization reaction. The method is linear over the 5-1000 μmol/L range. The detection and quantitation limits were 2.5 μmol/L and 5.0 μmol/L, respectively. When compared with colorimetric assay, the correlation coefficient (R2) was 0.9963. The within-assay and between-assay precision was <10.0% for four levels of quality control samples. No significant variation in BTD activity was detected due to hemolysis, icteric, and lipemic samples. The newly developed method eliminates the potential interference due to the presence of aromatic amines and significantly reduces the false positive results observed with the colorimetric method. It is simple, specific, sensitive, faster in sample preparation, and requires a small sample volume. The newly developed HPLC method was used in our laboratory as a secondary tier test for initial positive BTD samples from newborn screening programs. To our knowledge, no similar HPLC method has been reported to date.

Newborn Screening Conditions: Early Intervention and Probability of Developmental Delay

OBJECTIVES

The purpose of this study is to explore which newborn screening (NBS) conditions are automatically eligible for early intervention (EI) across states and to determine the extent to which each disorder should automatically qualify for EI because of a high probability of developmental delay.

METHODS

We examined each state's EI eligibility policy and reviewed the literature documenting developmental outcomes for each NBS condition. Using a novel matrix, we assessed the risk of developmental delay, medical complexity, and risk of episodic decompensation, revising the matrix iteratively until reaching consensus. Three NBS conditions (biotinidase deficiency, severe combined immunodeficiency, and propionic acidemia) are presented in detail as examples.

RESULTS

Most states (88%) had Established Conditions lists to autoqualify children to EI. The average number of NBS conditions listed was 7.8 (range 0-34). Each condition appeared on average in 11.7 Established Conditions lists (range 2-29). After the literature review and consensus process, 29 conditions were likely to meet national criteria for an Established Condition.

CONCLUSION

Despite benefiting from NBS and timely treatment, many children diagnosed with NBS conditions are at risk for developmental delays and significant medical complexity. The results demonstrate a need for more clarity and guidance regarding which children should qualify for EI. We suggest that most NBS conditions should automatically qualify based on the probability of resulting in a developmental delay. These findings suggest a future opportunity for collaboration between NBS and EI programs to create a consistent set of Established Conditions, potentially expediate referrals of eligible children, and streamline children's access to EI services.

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.

Failed, Interrupted, or Inconclusive Trials on Neuroprotective and Neuroregenerative Treatment Strategies in Multiple Sclerosis: Update 2015-2020

In the recent past, a plethora of drugs have been approved for the treatment of multiple sclerosis (MS). These therapeutics are mainly confined to immunomodulatory or immunosuppressive strategies but do not sufficiently address remyelination and neuroprotection. However, several neuroregenerative agents have shown potential in pre-clinical research and entered Phase I to III clinical trials. Although none of these compounds have yet proceeded to approval, understanding the causes of failure can broaden our knowledge about neuroprotection and neuroregeneration in MS. Moreover, most of the investigated approaches are characterised by consistent mechanisms of action and proved convincing efficacy in animal studies. Therefore, learning from their failure will help us to enforce the translation of findings acquired in pre-clinical studies into clinical application. Here, we summarise trials on MS treatment published since 2015 that have either failed or were interrupted due to a lack of efficacy, adverse events, or for other reasons. We further outline the rationale underlying these drugs and analyse the background of failure to gather new insights into MS pathophysiology and optimise future study designs. For conciseness, this review focuses on agents promoting remyelination and medications with primarily neuroprotective properties or unconventional approaches. Failed clinical trials that pursue immunomodulation are presented in a separate article.

Biotinidase deficiency is a rare, potentially treatable cause of peripheral neuropathy with or without optic neuropathy in adults

Background

We describe two adult brothers with lower limb neuropathy and one with progressive optic neuropathy. One brother was found to have profound biotinidase deficiency by identifying biallelic pathogenic variants of the BTD gene by whole exome sequencing, which was confirmed by markedly decreased serum biotinidase activity.

Case report and methods

The first brother had progressive optic atrophy and vision loss over 10 years and progressive peripheral neuropathy with weakness, pain, and fatigue for 20 years. Profound biotinidase deficiency was also identified in an older brother, who exhibited peripheral neuropathy since four years of age, but had no vision loss.

Results

The first brother's vision loss and neuropathy improved markedly with biotin in six months. However, the neuropathy of the other brother did not improve with 16 months of biotin therapy.

Conclusions

The first brother's neurological issues partially reversed with biotin. However, the longer-term symptoms of the other brother were irreversible. These cases emphasize the importance of considering biotinidase deficiency in the differential diagnosis of adolescents and adults with peripheral neuropathy with or without optic neuropathy/atrophy before symptoms become irreversible. Although WES initially identified the disorder in this family, measuring serum biotinidase activity was a necessary confirmatory step after WES and is less expensive than performing whole exome sequencing.

Biotinidase deficiency in differential diagnosis of neuromyelitis optica spectrum disorder

We present a case of biotinidase deficiency mimicking neuromyelitis optica spectrum disorder (NMOSD) with tetraparesis and transverse myelitis, who was diagnosed with profound biotinidase deficiency after developing optic atrophy and hearing loss before the age of one year, and was untreated for six months. Biotinidase deficiency should be considered in the differential diagnosis of seronegative NMOSD.

Spinal cord demyelination in children: A diagnostic challenge in neuropaediatrics for a good outcome

BACKGROUND

Biotinidase deficiency (BTD) is an autosomal recessive inborn error of metabolism provoking progressive biotin depletion, which causes, in turn, multiple carboxylase deficiency. Its infantile onset is characterized by intractable seizures associated with lethargy, psychomotor regression, hypotonia, feeding and respiratory problems, and cutaneous abnormalities.

CASE DESCRIPTION

We describe a 52-month-old female whose clinical and neuroradiological pictures were consistent with myelopathy, which is generally more frequent in older patients, as well as with symptoms of an infantile onset of biotinidase deficiency, revealed at 17 months.

RESULTS

A biochemical biotinidase test revealed a profound deficiency of biotinidase detecting a 10% residual enzymatic activity, which led to the diagnosis of BTD. Gene sequencing revealed a compound heterozigous mutation (c.454A > C/c.1612C > T).

CONCLUSION

Our findings suggest that even if myelopathy is uncommonly reported in BTD, and generally occurs in older children, its presence in childhood-onset floppiness should always be considered as a possible marker for an atypical presentation of BTD. Although, until recently, BTD myelopathy was believed to be prevalent in older children, a spinal cord involvement has also been described in at least nine cases in early infancy. Thus, another early diagnosis suggests that myelopathy may be more frequent than previously thought, and it is probably underdiagnosed because spinal MRI is not always routinely performed on these children. Early recognition of BTD disease is important as it would lead to prompt treatment, preventing irreversible brain damage and increasing the chances of complete recovery.

Biotinidase Deficiency: Prevalence, Impact And Management Strategies

Biotinidase deficiency is an autosomal recessive inherited neurocutaneous disorder. Clinically untreated patients with BD can present with variable neurological and dermatological signs, such as seizures, hypotonia, feeding problems, developmental delay, hearing loss, optic atrophy ataxia, alopecia, and skin rash. Clinical findings of patients with partial BD reported in the literature show that it can occur from infancy to adulthood. Outcomes of newborn screening programs support the fact that biotin treatment started after birth prevents patients with biotinidase deficiency from developing symptoms. Presence of late-onset cases with different clinical findings indicates that there is still much to learn about BD.

Pediatric NMOSD: A Review and Position Statement on Approach to Work-Up and Diagnosis

Neuromyelitis Optica Spectrum Disorder (NMOSD) is an inflammatory demyelinating disease of the central nervous system (CNS) primarily affecting the optic nerves and spinal cord, but also involving other regions of the CNS including the area postrema, periaqueductal gray matter, and hypothalamus. Knowledge related to pediatric manifestations of NMOSD has grown in recent years, particularly in light of newer information regarding the importance of not only antibodies to aquaporin 4 (AQP4-IgG) but also myelin oligodendrocyte glycoprotein (MOG-IgG) in children manifesting clinically with this syndrome. In this review, we describe the current state of the knowledge related to clinical manifestations, diagnosis, and chronic therapies for children with NMOSD, with emphasis on literature that has been published in the last 5 years. Following the review, we propose recommendations for the assessment/follow up clinical care, and treatment of this population.