The relationship between the number of CAG repeats and clinical manifestations: a survey of Chinese DRPLA family

Objective To describe the clinical, radiological, and genetic characteristics of a Chinese family with dentatorubropallidoluysian atrophy (DRPLA). Explore the distribution of CAG repeat size to the clinical features of patients. Methods We collected the clinical symptoms and DNA analysis for the DRPLA gene was performed on the family members. DRPLA patients reported in the literature were reviewed to analyze the association between CAG repeat size and clinical features. Results Six family members were confirmed by genetic analysis. The number of CAG repeat in the proband, her sister, her grandmother, her father, her uncle, and her cousin, was determined respectively as 63, 75, 50, 50, 50, 54. In our family, the sister of the proband had the earliest onset age and the most severe clinical symptoms, followed by the proband, and other family members showed no obvious clinical symptoms. Consistent with the conclusion of previous studies, the more repeats CAG, the earlier the age of onset and the severer phenotypes are. Conclusion We found six family members have CAG repeat expansion in the DRPLA gene on chromosome 12p13. Even in the same family, patients have different clinical presentations. The size of CAG repeats is negatively correlated with the age of onset and positively correlated with symptom severity. When the number of repeats is ≥ 63, the age at onset is < 21 years old, and obvious clinical symptoms generally appear. It seems to say the more repeats CAG, the earlier the age of onset and the severer phenotypes are. Limitations With a small number of cases in our family, the conclusion that the more CAG repeats, the earlier the onset and the more severe the clinical symptoms cannot be fully proved.