The Invitae Biotin-Thiamine-Responsive Basal Ganglia Disease (BTBGD) Test analyzes the SLC19A3 gene. BTBGD is characterized by recurrent encephalopathy including seizures, ataxia, and dystonia, an abnormal MRI with hyperintensities in the caudate and/or putamen, and normal biochemical lab tests. Genetic testing of this gene may confirm a diagnosis and help guide treatment and management decisions. Identification of disease-causing variants provide accurate risk assessment and carrier status for at-risk relatives.
Biotin-thiamine-responsive basal ganglia disease (BTBGD) is a highly variable neurological condition with a wide clinical spectrum. The primary features include recurrent episodes of encephalopathy manifesting as confusion, seizures, ataxia, and dystonia. Symptoms may present in infancy, childhood, or adolescence, and episodes are often triggered by infection or febrile illness. The severe infantile presentation is similar to Leigh disease, with neuroimaging findings of severe cerebral atrophy and microscopic brain lesions. Brain MRI findings among those presenting in childhood and adolescence include focal lesions predominantly in the putamen and caudate nucleus. Biotin and/or thiamine supplementation may improve symptoms, especially when instituted early in the disease course.
Among individuals with a clinical diagnosis of BTBGD, greater than 90% of individuals had pathogenic sequence variants.
BTBGD is inherited in an autosomal recessive manner.
BTBGD is a rare, likely underdiagnosed condition. The exact prevalence of BTBGD is unknown.
Invitae is a College of American Pathologists (CAP)-accredited and Clinical Laboratory Improvement Amendments (CLIA)-certified clinical diagnostic laboratory performing full-gene sequencing and deletion/duplication analysis using next-generation sequencing technology (NGS).
Our sequence analysis covers clinically important regions of each gene, including coding exons, +/- 10 base pairs of adjacent intronic sequence in the transcript listed below. In addition, analysis covers the select non-coding variants specifically defined in the table below. Any variants that fall outside these regions are not analyzed. Any specific limitations in the analysis of these genes are also listed in the table below.
Based on validation study results, this assay achieves >99% analytical sensitivity and specificity for single nucleotide variants, insertions and deletions <15bp in length, and exon-level deletions and duplications. Invitae's methods also detect insertions and deletions larger than 15bp but smaller than a full exon but sensitivity for these may be marginally reduced. Invitae’s deletion/duplication analysis determines copy number at a single exon resolution at virtually all targeted exons. However, in rare situations, single-exon copy number events may not be analyzed due to inherent sequence properties or isolated reduction in data quality. Certain types of variants, such as structural rearrangements (e.g. inversions, gene conversion events, translocations, etc.) or variants embedded in sequence with complex architecture (e.g. short tandem repeats or segmental duplications), may not be detected. Additionally, it may not be possible to fully resolve certain details about variants, such as mosaicism, phasing, or mapping ambiguity. Unless explicitly guaranteed, sequence changes in the promoter, non-coding exons, and other non-coding regions are not covered by this assay. Please consult the test definition on our website for details regarding regions or types of variants that are covered or excluded for this test. This report reflects the analysis of an extracted genomic DNA sample. In very rare cases, (circulating hematolymphoid neoplasm, bone marrow transplant, recent blood transfusion) the analyzed DNA may not represent the patient's constitutional genome.
|Gene||Transcript reference||Sequencing analysis||Deletion/Duplication analysis|