Objective
Duchenne muscular dystrophy (DMD) is a progressive hereditary muscular disease with X-linked recessive inheritance. Elevated serum creatine phosphokinase (CPK) level is a biomarker representing to a suspicion of DMD, deletion or duplication can be detected by molecular genetic testing as diagnosis. The mean age at diagnosis for DMD is a toddler, the feasibility of infantile screening is not established yet. In the past, there were no treatment modality for DMD except corticosteroids that could only minimally slow the disease progression. However, in recent years, advanced treatment methods such as exon skipping have been tried in DMD and are actually being realized. Therefore, it is important to diagnose patients at an early stage before symptoms progress.
Design
A febrile 4-month old male infant visited emergency department. In the Korean Infant & Child Health Checkup, which was conducted at 4 months of his age, the growth and development of the patient was in the normal range. Because his routine laboratory tests showed increased aminotransferase (aspartate aminotransferase 380 U/L (reference: 0–40 U/L), alanine aminotransferase 285 U/L (reference: 0–43 U/L), we also performed CPK; CPK was dramatically increased as 19,058 U/L (reference: 0–190 U/L). Genetic testing was conducted for hereditary metabolic abnormalities and myopathy that can cause abnormal findings in these laboratory findings.
Results
Genomic DNA was extracted from the subject’s peripheral blood using the Wizard DNA purification Kit (Promega Corporation, Madison, USA) based on the manufacturer’s manual. About 57,000 target exon and 180 SNV of 4,503 genes were captured using the the xGen-Inherited Disease panel (Integrated dna technologies, Coralville, Iowa, USA). Massively parallel sequencing was performed using 2*150 paired end reads with NextSeq (Illumina, San Diego, CA, USA) equipment.
As a result, the patient's targeted exome sequencing showed a hemizygous deletion in exon 45-50 of DMD gene at Xp21.1: arr Xp21.1(31795774_32036509)×0. Multiplex Ligation Dependent Probe Amplification Assay (MLPA) of DMD gene was additionally performed, and exon 45-50 deletion was finally confirmed. This genetic defect of DMD is considered to be a type that can be applied to exon skipping using eteplirsen (Exondys 51®), which is currently released in the United States.
He is currently followed up continuously in department of rehabilitation medicine, pediatrics, and neurology. Developmental evaluation that was last performed at his 10-months after birth showed a delay of about 4 months at gross motor area; GMFM (Gross Motor Function Measure) Gross motor age 6–6.5 months, DDST (Denver Developmental Screening Test) Personal social, Fine motor, Language ability was normal, however gross motor performance age was 6–6.6 months.
Conclusion
This is the earliest documented diagnosis made to genetic sequencing analysis of DMD gene in a Korean infant. |
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Fig 1. The targeted exome sequencing (Illumina, San Diego, CA, USA) of a 4-months-old Korean infant with Duchenne muscular dystrophy. The patient's targeted exome sequencing showed a hemizygous deletion in exon 45-50 of DMD gene at Xp21.1: arr Xp21.1(31795774_32036509)×0.
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