Objective　To?explore?the?clinical?characteristics,?diagnosis?and?treatment?of?biotinidase?deficiency?(BTDD).? Method? The?clinical?data?of?BTDD?caused?by?biotinidase?gene?mutation?in?a?child?was?analyzed?retrospectively,?and?the? literature?was?reviewed.?Results? A?13-month-old?boy?had?onset?at?8?months?after?birth.?He?presented?with?recurrent?wheezing,? gross?motor?development?regression,?refractory?metabolic?acidosis?combined?with?compensatory?respiratory?alkalosis.?Urine? organic?acid?analysis?showed?that?the?levels?of?lactic?acid,?ketone?bodies,?succinic?acid,?fumaric?acid,?2.3DH2MB,?3meglutarconate,?and?malic?acid?were?increased.?The?activity?of?biotinidase?decreased?significantly.?The?whole-exome?gene?test? revealed?that?the?child?had?a?homozygous?variant?c.1493dupT?in?the?BTD?gene,?which?came?from?both?his?parents?with?normal? phenotype,?and?it?was?a?pathogenic?variant.?He?was?confirmed?with?the?diagnosis?of?BTDD.?The?wheezing?symptoms?in?the?child? were?relieved?within?a?few?hours?after?biotin?supplementation.?Conclusion? Children?with?suspected?BTDD?should?be?tested?by? hematuria?tandem?mass?spectrometry?as?soon?as?possible.?The?tests?for?biotinidase?activity?and?gene?should?be?improved.