Biotinidase Test

Biotinidase test is carried out to identify the deficiency of biotinidase, which is an autosomal recessive disorder caused by mutations in the biotinidase gene (BTD). BIOT is an inherited condition in which the body is unable to reuse and recycle the vitamin biotin. This condition may be detected in newly born infants and also in adults. If this condition is not recognized and treated, its signs and symptoms typically appear within the first few months of life, although it can also become apparent later in childhood.The screening of biotinidase deficiency is included in the screening programme of newly born infants.

Before carrying out the required procedures, it is essential to prepare the medical experts by undertaking the following steps: For enzymatic testing, serum or plasma samples should be thawed immediately prior to analysis with no other sample preparation steps is required. Identification of biochemical abnormalities such as metabolic keto lactic acidosis, hyperammonemia and organic aciduria. Identification of cellular immunologic abnormalities. Audiological evaluation for sensorineural hearing loss. Evaluation of developmental and psychomotor deficits. Ophthalmological evaluation for optic atrophy and other eye abnormalities. Physical examination for hypotonia, ataxia, eye findings such as optic atrophy, eczematous skin rash, breathing abnormalities such as stridor, thrush and candidiasis.

On carrying out the biotinidase test the following results can be obtained. Two pathogenic BTD gene variants identified on opposite chromosomes predicts a diagnosis of biotinidase deficiency. One severe and one mild BTD gene variant identified predicts partial biotinidase deficiency . One copy of a pathogenic BTD gene variant identified predicts that individual is at least a carrier of biotinidase deficiency. No pathogenic gene variants detected by sequencing likelihood is reduced that the individual is a carrier of or affected with biotinidase deficiency. Based on the above mentioned analysis the doctors will be able to determine the appropriate medications required for the patient.

Screening-The best method of screening is a semiquantitative colorimetric assessment of biotinidase activity that can be performed on whole blood spotted on filter paper. Follow-up and Diagnostic Testing-A positive screening result for biotinidase deficiency should be followed up with definitive testing for diagnosis. Quantitative measurement of enzyme activity should be performed on a fresh serum sample. Biotinidase activity can be measured using a fluorescent technique with biotinyl 6-aminoquinoline as an artificial substrate. This substrate is more expensive than that for the colorimetric method, but has also been adapted for the newborn screening and the testing of dried blood spots. Enzymatic testing makes use of serum or plasma sample for analysis.