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

## TL;DR

A 3-year-old boy with both Becker Muscular Dystrophy and Okur–Chung Syndrome shows how low cognitive functioning can be when both conditions coexist.

## Contribution

This case highlights the lower cognitive limits of muscular dystrophy and the importance of dual diagnosis in neurodevelopmental delays.

## Key findings

- Patients with BMD have an average FSIQ of 88.3 ± 13.9, while those with brain-impacting Dp140 variants have an FSIQ of 77.7 ± 10.8.
- An FSIQ one standard deviation below expected ranges should prompt screening for alternative causes.
- Dual diagnosis in muscular dystrophy cases can explain severe neurodevelopmental delays beyond dystrophy alone.

## Abstract

This case discusses the limits of neurodevelopmental functioning attributable to Duchenne's Muscular Dystrophy (DMD) dysfunction.

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.

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.

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.

This article shares an interesting case of a dual diagnosis and explores the expected cognitive abilities attributed to each diagnosis. It will be helpful to clinicians to think about when to consider a dual diagnosis in a patient with muscular dystrophy.