5-year-old: Inability to keep up with peers 

Birth and Infancy

N was born following an uneventful pregnancy, labor and delivery. He met his developmental milestones during infancy, but was always a bit behind the average milestone attainment. As his older brother had always been a bit ahead of the curve, his parents were not too concerned. N had always had large calves, even as a baby.

Continued Growth and Development

When N was 5 years old, his kindergarten teacher expressed concern that N wouldn’t run around the playground like his peers and seemed to be limiting himself physically. His parents mentioned his teacher’s comments to the pediatrician, who asked if there was any family history of musculoskeletal disorders. Based on a negative family history and continued developmental progress, the pediatrician dismissed the concerns.

Clinical Pearl: A negative family history does not rule out a genetic neuromuscular disorder.

Clinical Pearl: Children can make developmental progress, even with progressive weakness. Developmental progress does not exclude the possibility of an underlying neuromuscular condition.

At 6 years of age, N’s gym teacher noticed that N was having trouble keeping up with his peers physically. His parents again took their concerns to the pediatrician, who referred N to a neurologist.

Diagnosis

After a thorough evaluation, the neurologist ordered labs, including a CK level. N’s CK level was extremely elevated (>20,000 IU/l) and he was referred to a local multidisciplinary neuromuscular clinic. His clinical exam was consistent with a muscular dystrophy, and the neuromuscular team suspected Duchenne muscular dystrophy. The neuromuscular team recommended DNA testing to confirm the diagnosis. After a comprehensive testing series was performed in the dystrophin gene, no mutation was identified. At that point, consideration was given to other forms of muscular dystrophy that can mimic DMD. Mutations were identified in both copies of the FKRP gene, confirming a diagnosis of limb-girdle muscular dystrophy type 2I.