The Invitae Biotinidase Deficiency Test analyzes the gene BTD, which is associated with biotinidase deficiency. This test is useful for the diagnosis of patients in whom biotinidase deficiency is suspected due to clinical symptoms, abnormal newborn screening results, or biochemical findings.
These panels have been designed to provide a broad genetic analysis of this class of disorders. Depending on the individual’s clinical and family history, one of these broader panels may be appropriate. They can be ordered at no additional cost.
Profound biotinidase deficiency is generally seen in patients with less than 10% of residual biotinidase activity. Untreated patients with profound biotinidase deficiency can have hypotonia, seizures, alopecia, eczema, metabolic acidosis, and developmental delay. Over time, untreated patients may develop sensorineural hearing loss, candidiasis, ataxia, conjunctivitis, and visual problems such as optic atrophy. Early treatment with pharmacologic doses of biotin is important to prevent irreversible neurologic damage. With early intervention and treatment, patients generally remain asymptomatic.
Partial biotinidase deficiency is the most common clinical subtype of biotinidase deficiency. Many patients with partial biotinidase deficiency have been picked up on newborn screening and remain asymptomatic. Those with symptoms, however, may have intermittent hypotonia, skin rashes, or alopecia during times of prolonged intercurrent illness. Partial biotinidase deficiency is generally seen in patients with 10%–30% of residual biotinidase activity.
Biotinidase deficiency is an enzyme deficiency that affects the recycling of the coenzyme biotin, a water-soluble B vitamin. If untreated, this disorder can result in deficiencies of the four biotin-dependent carboxylases: acetyl-CoA carboxylase, 3-methylcrotonyl-CoA carboxylase, propionyl-CoA carboxylase, and pyruvate carboxylase. A biochemical feature of biotinidase deficiency is the abnormal elevation of urine organic acids, including 3-hydroxyisovaleric acid, lactic acid, 3-hydroxypropionic acid, methylcitric acid, 3-methylcrotonylglycine, propionylglycine, and tiglylglycine. Propionylcarnitine (C3) and 3-hydroxyisovalerylcarnitine (C5-OH) can also be elevated. Serum biotinidase activity will be low. Currently, most patients with biotinidase deficiency are identified through newborn screening.
Approximately 100% of patients with symptoms that are consistent with biotinidase deficiency and a biochemical diagnosis of biotinidase deficiency will have two pathogenic mutations in the BTD gene.
Symptoms and biochemical diagnosis:
Biotinidase deficiency is inherited in an autosomal recessive pattern.
Profound biotinidase deficiency is a fully penetrant disorder; symptom onset ranges from one week to ten years, with an average age of onset of 3.5 months. Only some patients with partial biotinidase deficiency will have symptoms; those who do may not present until adulthood. Because patients with biotinidase deficiency can have a wide variability in clinical and biochemical symptoms, molecular testing may be warranted in suspected patients who lack the classic organic aciduria.
The worldwide prevalence for biotinidase deficiency is 1 in 60,000. Partial biotinidase deficiency has a birth incidence of roughly 1 in 129,500. Profound biotinidase deficiency has a birth incidence of 1 in 112,271. The birth incidence of both partial and profound biotinidase deficiency has been estimated in several subpopulations as follows:
This panel may be appropriate for:
For considerations for testing please refer to:
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, and select noncoding variants. Our assay provides a Q30 quality-adjusted mean coverage depth of 350x (50x minimum, or supplemented with additional analysis). Variants classified as pathogenic or likely pathogenic are confirmed with orthogonal methods, except individual variants that have high quality scores and previously validated in at least ten unrelated samples.
Our analysis detects most intragenic deletions and duplications at single exon resolution. However, in rare situations, single-exon copy number events may not be analyzed due to inherent sequence properties or isolated reduction in data quality. If you are requesting the detection of a specific single-exon copy number variation, please contact Client Services before placing your order.
|Gene||Transcript reference||Sequencing analysis||Deletion/Duplication analysis|