Biotinidase deficiency: A treatable cause of opticospinal syndrome in young adults✰

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.

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.

Adult-Onset Genetic Central Nervous System Disorders Masquerading as Acquired Neuroinflammatory Disorders: A Review

Importance

Adult-onset genetic disorders may present with clinical and magnetic resonance imaging (MRI) features suggestive of acquired inflammatory diseases. An ever-growing number of potentially treatable adult-onset genetic neuroinflammatory disorders have been described in the past few years that need to be rapidly identified.

Observations

Adult-onset acquired neuroinflammatory disorders encompass a large group of central nervous system (CNS) diseases with varying presentation, MRI characteristics, and course, among which the most common is multiple sclerosis. Despite recent progress, including the discovery of specific autoantibodies, a significant number of adult-onset neuroinflammatory disorders with progressive or relapsing course still remain without a definite diagnosis. In addition, some patients with genetic disorders such as leukodystrophies, hemophagocytic lymphohistiocytosis, or genetic vasculopathies can mimic acquired neuroinflammatory disorders. These genetic disorders, initially described in pediatric populations, are increasingly detected in adulthood thanks to recent progress in molecular genetics and the larger availability of high-throughput sequencing technologies.

Conclusions and Relevance

Genetic adult-onset neuroinflammatory diseases are at the border between primary CNS inflammatory diseases and systemic disorders with multiorgan involvement and predominantly neurologic manifestations. Neurologists must be aware of the main clues and red flags so they can confirm a diagnosis early, when some of these genetic disorders can be successfully treated.

Shortcutting the diagnostic odyssey: the multidisciplinary Program for Undiagnosed Rare Diseases in adults (UD-PrOZA)

Background

In order to facilitate the diagnostic process for adult patients suffering from a rare disease, the Undiagnosed Disease Program (UD-PrOZA) was founded in 2015 at the Ghent University Hospital in Belgium. In this study we report the five-year results of our multidisciplinary approach in rare disease diagnostics.

Methods

Patients referred by a healthcare provider, in which an underlying rare disease is likely, qualify for a UD-PrOZA evaluation. UD-PrOZA uses a multidisciplinary clinical approach combined with state-of-the-art genomic technologies in close collaboration with research facilities to diagnose patients.

Results

Between 2015 and 2020, 692 patients (94% adults) were referred of which 329 (48%) were accepted for evaluation. In 18% (60 of 329) of the cases a definite diagnosis was made. 88% (53 of 60) of the established diagnoses had a genetic origin. 65% (39 of 60) of the genetic diagnoses were made through whole exome sequencing (WES). The mean time interval between symptom-onset and diagnosis was 19 years. Key observations included novel genotype–phenotype correlations, new variants in known disease genes and the identification of three new disease genes. In 13% (7 of 53), identifying the molecular cause was associated with therapeutic recommendations and in 88% (53 of 60), gene specific genetic counseling was made possible. Actionable secondary findings were reported in 7% (12 of 177) of the patients in which WES was performed.

Conclusion

UD-PrOZA offers an innovative interdisciplinary platform to diagnose rare diseases in adults with previously unexplained medical problems and to facilitate translational research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02365-y.

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 presenting as Neuromyelitis Optica Spectrum Disorder

Biotinidase deficiency disorder is a rare inherited metabolic disorder with typical neurological manifestations of hypotonia, developmental delay, rashes, seizures, hearing and vision impairment. We present two cases with different and unusual clinical profiles, whose neuroimaging resembled Neuromyelitis Optica Spectrum Disorder. Case 1 was initially treated with immunomodulation with steroids and intravenous immunoglobulins, with partial improvement. However reinvestigation for worsening of symptoms showed more extensive changes on spine magnetic resonance imaging. Raised lactate and alanine levels on repeat cerebrospinal fluid testing resulted in further investigations that revealed a biotinidase deficiency. Case 2 presented mainly with respiratory symptoms: a barium swallow suggested bulbar dysfunction. Neuroimaging of brain and spine was similar to that in case 1 and the child was promptly investigated for and confirmed to have biotinidase deficiency. Both cases responded to biotin supplementation. It is important to be cognisant of atypical neurological presentations of biotinidase deficiency including those that mimic immune mediated neurodemyelination disorders, as biotinidase deficiency is potentially treatable.

Severe Distal Motor Involvement in a Non-compliant Adult With Biotinidase Deficiency: The Necessity of Life-Long Biotin Therapy

Biotinidase deficiency is an autosomal recessive disorder in which affected individuals are unable to recycle biotin. Untreated, children usually exhibit hypotonia, seizures, ataxia, developmental delay, and/or hearing loss. Individuals diagnosed by newborn screening have an excellent prognosis with life-long biotin supplementation. We report a young adult diagnosed with profound biotinidase deficiency by newborn screening who was asymptomatic while on therapy. At 18 years of age, 6 months after voluntarily discontinuation of biotin, he developed a progressive distal muscle weakness. Molecular analysis of the BTD gene showed a pathogenic homozygous duplication c.1372_1373dupT p.(Cys458LeufsTer26) (1). Despite 16 months since reintroduction of biotin, muscle strength only partially recovered. Transition to adulthood in chronic metabolic diseases is known to be associated with an increased risk for non-compliance. Neurological findings in this adult are similar to those described in others with adult-onset biotinidase deficiency. Long-term prognosis in non-compliant symptomatic adult with biotinidase deficiency likely depends on the delay and/or severity of intervening symptoms until reintroduction of biotin.