New Clinical Phenotype in a Child Presenting With an FHL1 Mutation.

There is a range of phenotypes associated with pathogenic variants in the FHL1 gene, including X-linked dominant scapuloperoneal myopathy, X-linked myopathy with postural muscle atrophy, reducing body myopathy, Emery-Dreifuss muscular dystrophy, rigid-spine syndrome, and hypertrophic cardiomyopathy. This gene encodes the four-and-a-half LIM domain protein 1 which is highly expressed in skeletal and cardiac muscle. The function of this protein includes influencing cellular architecture, myoblast differentiation, mechanotransduction, and skeletal muscle fiber size. We report a case of a 6-year-old boy with a novel FHL1 gene mutation who presented to the neuromuscular clinic for evaluation of stiffness, joint contractures, and mild proximal weakness. Symptoms first noted in the newborn period have been slowly progressive. The child's presentation has not been described before and represents a new clinical phenotype within the spectrum of FHL1-related disorders.