Why is the gracilis muscle relatively uninvolved in neuromuscular disorders?

Non-lethal congenital hypotonia due to glycogen storage disease type IV

Glycogen storage disease type IV (GSD-IV) is an autosomal recessive genetic disorder due to a deficiency in the activity of the glycogen branching enzyme (GBE). A deficiency in GBE activity results in the accumulation of glycogen with fewer branching points and long, unbranched outer chains. The disorder results in a variable phenotype, including musculoskeletal, cardiac, neurological, and hepatic involvement, alone or in continuum, which can be identified at any stage of life. The classic form of GSD-IV is a hepatic presentation, which presents in the first 18 months of life with failure to thrive, hepatomegaly, and cirrhosis that progresses to liver failure, resulting in death by age 5 years. A severe congenital musculoskeletal phenotype with death in the neonatal period has also been described. We report an unusual case of congenital musculoskeletal presentation of GSD-IV with stable congenital hypotonia, gross motor delay, and severe fibro-fatty replacement of the musculature, but no hepatic or cardiac involvement. Molecular analysis revealed two novel missense mutations with amino acid changes in the GBE gene (Q236H and R262C), which may account for the mild phenotype.

Early onset muscular dystrophy with autosomal dominant heredity. Report of a family and CT findings of skeletal muscle

The clinical features and muscle pathology in a female infant and her mother with early onset and slowly progressive muscular dystrophy (MD), possibly transmitted through autosomal dominant inheritance, are described. The mother exhibited multiple joint contractures at birth. The daughter had mild proximal muscle weakness at 2 3/12 years old. The muscle biopsy specimens from both patients showed myopathic changes with evidence of fiber necrosis and regeneration. Computed tomographic (CT) findings of their skeletal muscles suggested that proximal muscles were involved at an early stage, with later gradual involvement of generalized muscles, without a characteristic selectivity pattern in thigh muscles. This may possibly be a clinically benign and distinct variant of MD with a slowly degenerating pattern of skeletal muscles on CT.