Assessing age of onset and clinical symptoms over time in patients with heterozygous pathogenic DHDDS variants

Mono-allelic DHDDS variants are associated with seizures, intellectual disability, and movement disorders. The age of onset and progression rates of symptoms vary greatly among patients, spanning from infancy to late adulthood. Yet, the reasons behind this clinical variability and the underlying pathophysiological mechanisms of the disease have remained elusive. We investigated the age of onset and the progression of symptoms over time in 59 patients with heterozygous DHDDS variants, drawing from medical literature and incorporating five previously unreported cases from the FCDGC Natural History Study. Clinical symptoms typically emerged early in life. Ataxia, tremor, dystonia, and dyskinesia manifested slightly later in childhood. Global developmental delay usually presented as the initial symptom. We observed diverse rates of symptom accumulation over time: some patients exhibited the full spectrum of symptoms in early childhood, while others developed novel symptoms well into adulthood. Interestingly, neither the sex nor the underlying DHDDS variants correlated with the age of symptom onset or specific clinical symptoms. Additionally, we found that 19% of patients presented with autism spectrum disorder. This study offers insight into the age of symptom onset and the rate of symptom accumulation in patients with DHDDS variants. We found no correlation between the age of onset and progression of clinical symptoms with specific DHDDS variants or patient sex. Autism spectrum disorder is common in patients and warrants attention in clinical management.