A Dual Diagnosis of Okur–Chung Neurodevelopmental Syndrome and Becker Muscular Dystrophy: Inquiry Into the Lower Limits of Neurodevelopmental Functioning Attributable to Muscular Dystrophy

Abstract

Purpose:: This case discusses the limits of neurodevelopmental functioning attributable to Duchenne's Muscular Dystrophy (DMD) dysfunction. Method: A 3-year-old male presented with global developmental delay, growth failure, and dysmorphic facial features. An SNP microarray revealed an interstitial duplication in exon 55 of DMD suggestive of Becker Muscular Dystrophy (BMD), but his degree of delays led to follow-up exome sequencing revealing a pathogenic CSNK2A1 variant diagnostic for Okur–Chung Neurodevelopmental Syndrome. Findings: Large cohorts predict a full-scale IQ (FSIQ) of 88.3 ± 13.9 among all patients with BMD and 86.1 ± 15.0 among all patients with DMD, while variants impacting the brain dystrophin isoform Dp140 are associated with FSIQ of 77.7 ± 10.8 in BMD and 78.8 ± 18.6 in DMD. Conclusion: An FSIQ one standard deviation below these expected ranges should prompt screening for alternative causes of neurodevelopmental delays, and an FSIQ two standard deviations below these ranges should prompt broad-spectrum genetic testing.