[Analysis of D4Z4 mutation in a child with facioscapulohumeral muscular dystrophy presented initially as mental retardation].

OBJECTIVE

To identify pathological mutation of D4Z4 in a child with facioscapulohumeral muscular dystrophy (FSHD) presented initially as mental retardation.

METHODS

Wechsler Intelligence Scale for Children Revised in China (WISC-IV) was used to assess the patient's IQ. Other clinical data was also collected. With genomic DNA extracted from peripheral blood samples, the child and his parents were subjected to medical exome sequencing and copy number variation analysis by next generation sequencing (NGS). The D4Z4 repeats and their origin source were determined by molecular combing.

RESULTS

By the WISC-IV test, the child was found to have a total IQ of 41, with a speech comprehension IQ of 45, and perceptual inference index IQ of 52. No pathological mutation was detected by NGS. By molecular combing method, the child was found to carry a D4Z4 spanning 5.2 kb with a copy number of 2. Analysis of his parents indicate that the mutation was de novo.

CONCLUSION

The D4Z4 copy number variation may account for the FSHD and mental retardation in the child. The molecular combing method can be used to identify the number of repeat units and facilitate the diagnosis of FSHD.