The distribution of D4Z4 repeats in China and direct prenatal diagnosis of FSHD by optical genome mapping.

BACKGROUND

Facioscapulohumeral muscular dystrophy (FSHD) is the second most common form of muscular dystrophy, which is characterized by a reduction in the number of D4Z4 repeats on chromosome 4q35. Prenatal diagnosis of FSHD has been challenging due to the large quantity and high-quality DNA required for Southern blot (SB) analysis. Optical genome mapping (OGM) technology has shown promise in identifying repeat contraction disorders and presents a potential tool for the prenatal diagnosis of FSHD.

METHODS

In this retrospective cohort study, we investigated the distribution of D4Z4 repeats in 100 unrelated healthy individuals from the Chinese Han population using peripheral blood samples and DLS labelling method. Additionally, prenatal diagnosis using OGM was performed in 12 FSHD families at Peking Union Medical College Hospital between January 2021 and December 2023. The prenatal samples included 2 amniotic cell cultures and 10 chorionic villus samples (CVS), with 9 labeled using DLS and 4 using NLRS method.

RESULTS

Among the 100 healthy controls, the distribution of D4Z4 repeats varied, with 3 individuals having borderline 10 repeat counts on 4qA, and the most frequent count being 14 units. One individual with mosaicism was also identified. In the cohort of 12 FSHD families,14 prenatal diagnoses were performed. Of these 14 cases, 4 fetuses tested positive for 4qA contraction, with repeat counts ranging from 2 to 4. In both families that underwent two rounds of prenatal diagnosis, the first diagnosis indicated the presence of FSHD, leading to pregnancy termination, while the second diagnosis confirmed the presence of healthy fetuses. The overall positive rate was 28.57%.

CONCLUSION

Our findings demonstrate that OGM is an accurate and effective method for the prenatal diagnosis of FSHD. The application of OGM in prenatal settings could offer significant benefits to families affected by FSHD with reproductive concerns.