Molecular characterisation and neuropsychological outcome of 21 patients with profound biotinidase deficiency detected by newborn screening and family studies

Dorothea Möslinger, Adolf Mühl, Terttu Suormala, Regula Baumgartner, Sylvia Stöckler-Ipsiroglu

Early recognition by newborn screening and oral biotin supplementation may prevent clinical and neurological deficits in profound biotinidase deficiency (residual plasma biotinidase activity <10%). In order to evaluate possible correlations of molecular characteristics, onset and continuation of treatment and clinical outcome, we investigated 21 patients detected by newborn screening and consecutive family investigations. In 18 patients found by newborn screening, the range of biotinidase activities was 0%-9% residual activity. Application of a sensitive HPLC assay enabled us to discriminate five patients with residual biotinidase activities <1%. Two patients with zero activities were homozygous for the G98:d7i3 mutation and three patients with activities <1% carried mutations G98:d7i3, R157H, and Q456H. The mutation spectrum of the remaining patients included T532M, A171T+D444H, V62M,C432W, and D444H. Evaluation of clinical and neuropsychological outcome showed that only patients with biotinidase activities <1% exhibited characteristic clinical symptoms within the first weeks of life whereas five patients with residual activities of 1.2%-4.6% did not develop clinical symptoms even when not treated until 3.5-21 years. In all patients treated with biotin within the first weeks of life, neuropsychological outcome was normal whereas abnormal in three out of five patients tested for IQ and treated after the age of 3.5 years.