We present a family in which the first child was diagnosed with dopa-responsive dystonia based on biochemical findings only. Dopa-responsive dystonia is a severe heterogeneous genetic disease. The possibly involved genes are GCH1 and TH.

In their second pregnancy, the parents came for genetic counseling and prenatal diagnosis late, at 12 weeks of gestation. Genetic testing in the affected child was performed, but the results were difficult to interpret. The identified mutations were classified as VOUS – variants of unknown clinical significance. Although possibly causative, a homozygous variant in the TH gene was not reported before in children with dopa-responsive dystonia. Due to limited time, establishing the fetal prognosis was challenging.

Our report emphasizes the importance of a multidisciplinary approach in the context of new diagnostic techniques, such as Next Generation Sequencing. We illustrate the fact that behind any laboratory result remains sophisticated clinical judgment. We also describe a previously not reported variant of the TH gene in a child with severe, early-onset dystonia.