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Test ID: BIOTS    
Biotinidase, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Preferred test for diagnosing biotinidase deficiency

 

Follow-up testing for certain organic acidurias

Genetics Test Information Provides information that may help with selection of the correct test or proper submission of the test request

Preferred test to rule out biotinidase deficiency.

Second tier molecular testing is available.

See BTDMS / Biotinidase Deficiency, BTD Full Gene Analysis for specimen requirements.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Biotinidase deficiency is an autosomal recessive disorder caused by mutations in the biotinidase gene (BTD). Age of onset and clinical phenotype vary among individuals depending on the amount of residual biotinidase activity. Profound biotinidase deficiency occurs in approximately 1 in 137,000 live births and partial biotinidase deficiency occurs in approximately 1 in 110,000 live births, resulting in a combined incidence of about 1 in 61,000. The carrier frequency for biotinidase deficiency within the general population is about 1 in 120.

 

Untreated profound biotinidase deficiency typically manifests within the first decade of life as seizures, ataxia, developmental delay, hypotonia, sensorineural hearing loss, vision problems, skin rash, and/or alopecia. Partial biotinidase deficiency is associated with a milder clinical presentation, which may include cutaneous symptoms without neurologic involvement. Certain organic acidurias, such as holocarboxylase synthase deficiency, isolated carboxylase synthase deficiency and 3-methylcrotonylglycinuria, present similarly to biotinidase deficiency. Serum biotinidase levels can help rule out these disorders.  

 

Treatment with biotin is successful in preventing the clinical features associated with biotinidase deficiency. In symptomatic patients, treatment will reverse many of the clinical features except developmental delay and vision and hearing complications. As a result, biotinidase deficiency is included in most newborn screening programs. This enables early identification and treatment of presymptomatic patients.

 

Molecular tests form the basis of confirmatory or carrier testing. When biotinidase enzyme activity is deficient, sequencing of the entire BTD gene (BTDMS / Biotinidase Deficiency, BTD Full Gene Analysis) allows for detection of disease-causing mutations in affected patients. Identification of familial mutations allows for testing of at-risk family members (BTDKM / Biotinidase Deficiency, BTD Gene, Known Mutation).

 

While genotype-phenotype correlations are not well established, it appears that certain mutations are associated with profound biotinidase deficiency, while others are associated with partial deficiency.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

3.5-13.8 U/L

Interpretation Provides information to assist in interpretation of the test results

The reference range is 3.5 U/L to 13.8 U/L.

 

Partial deficiencies and carriers may occur at the low end of the reference range.

 

Values <3.5 U/L are occasionally seen in specimens from unaffected patients.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

A diet high in biotin may result in normal clinical presentation even when the biotinidase level is low.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Wolf B: Chapter 156: Disorders of biotin metabolism. In The Metabolic and Molecular Basis of Inherited Disease. Vol 3. Eighth edition. Edited by CR Scriver, AL Beaudet, WS Sly, et al. New York, McGraw-Hill Book Company. 2001

2. Wolf B: Biotinidase Deficiency. Available from URL: http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=biotin Reviewed September 25, 2008

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test