In the present study, among the seven cases of disagreement between the observed and expected biochemical phenotype, we highlight patient 10 because her genotype p.D444H/c.595G > A (p.V199M) and p.V199M/p.V199M have previously been reported in patients with residual biotinidase activity levels of 32% and 11.5% respectively [26], and it is possible that the p.V199M variant is not as damaging as other profound BD alleles. Here, BTD is linked to Behcet disease.