Supplementary Material for: Novel Cranial Imaging Findings and a Splice-Site Variant in a Patient with Tyrosinemia Type III, and a Summary of Published Cases

Tyrosinemia type III is an extremely rare autosomal recessive disease, with only 19 patients yet reported. It is caused by a deficiency of the 4-hydroxyphenylpyruvate dioxygenase enzyme, resulting from biallelic mutations in the HPD gene. Although the clinical spectrum of the disease is not fully known, most patients present with neurodevelopmental symptoms. We report on a 20-month-old patient who was investigated due to developmental delay and dysmorphic features. The girl had a novel splice-site mutation in the HPD gene and ventriculomegaly in cranial imaging, which was not previously associated with tyrosinemia type III. Our patient had mild subjective improvement in social skills and language development after dietary therapy was started and her tyrosine levels decreased. We also summarize clinical, biochemical, and genetic findings of previously published patients with biallelic HPD mutations.