Partial biotinidase deficiency

Activities obtained in plasma of (1) patients with profound biotinidase deficiency (less than 10% residual activity), (2) subjects with partial biotinidase deficiency (10-30% residual activity), (3) some of their parents (obligate heterozygotes) and (4) individual patients with a biotinidase Km defect are also shown in Table 3.7.2. Patients with complete biotinidase deficiency defined by assay with a sensitive HPLC method... 

Suormala TM, Baumgartner ER, Wick H, Scheibenreiter S, Schweitzer S (1990) Comparison of patients with complete and partial biotinidase deficiency biochemical studies. J Inherit Metab Dis 13 76-92... 

Patients with HCS deficiency (MIM 253270) can show severe illness very early, within the first hours or days of life, but they can also present later with clinical findings similar to those seen in biotinidase deficiency. The majority of HCS-defi-cient patients show reduced affinity of HCS for biotin and respond well to oral biotin therapy, but usually require higher doses (20-100 mg/day) than are required for biotinidase deficiency. A few patients respond only partially to high-dose biotin therapy... 

Family studies often reveal older siblings or parents with partial or profound biotinidase deficiency [17, 25, 33]. These individuals are usually asymptomatic but may suffer from moderate biotin deficiency [23] and might benefit from biotin therapy. Therefore, all family members should be investigated. 

Heterozygous individuals usually have intermediate enzyme activity, especially in families with a profound deficiency, with some overlap with the normal range. Thus, biotinidase activity with 0.15 mM substrate was within the normal range in 6 (5%) out of 117 parents from families with a profound deficiency, and in 15 (20%) out of 75 parents from families with a partial deficiency. 

Biotinidase activity in plasma of some newborns may be lower than that in adults (see Pitfalls and Limitations ) [12, 23]. Therefore when activities within the partially deficient or heterozygous range are obtained in newborns, this finding should be confirmed by repeating the assay at the age of about 6 months or later. 

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