Muscle growth, development and mass steadily increase from the moment a child is born. More than 600 muscles form in the human body and by the time your child surpasses puberty into late adolescence, his muscle mass is at peak levels. Genetic abnormalities can cause under- or overdeveloped muscles in children. Myotonia congenita and muscular dystrophy are two inherited diseases that can result in pseudohypertrophic muscles.
Pseudohypertrophy and Overdevelopment
Muscle enlargement, or pseudohypertrophy, can occur in one specific muscle group or several regions. Adults voluntarily engage in activities such as body building to form well or overdeveloped muscles. In children, the occurrence of overdevelopment is typically an involuntary occurrence that gradually appears after birth. In the case of your child having a genetic dystrophy, such as Duchenne muscular dystrophy, pseudohypertrophy is a symptom. In a non-dystrophy genetic abnormality, such as myotonia congenita, muscle overdevelopment is a symptom the stems from the inability of the muscles to properly contract and relax.
Genetic Mutation in DMD
Muscle overdevelopment is one of the common markers of DMD. The dystrophin gene, which is important for muscle development, holds the muscles together and maintains the cellular structure of the muscle. Dystrophin is contained within the X chromosome contributed during conception. A mutated X chromosome missing dystrophin increases the risk of the presence of the disease. Boys are more susceptible to inheriting this disorder than girls because boys only get one X chromosome whereas girls have an extra chromosome that can compensate if the mutation is present, according to the Duchenne Muscular Dystrophy Research Fund.
Genetic Mutation in Myotonia Congenita
The skeletal muscles are affected by the mutation that causes myotonia congenita. Two forms of myotonia congenita exist. Thomsen disease is one form inherited by the child from one parent with the mutated gene and Becker disease is the other form, in which both contributing parents have the mutation. The particular gene responsible for both forms of myotonia congenita is CLCN1, which provides genetic instruction for creating the skeletal muscle cells. Abnormality in this gene prevents the muscles from receiving the proper signals telling it to contract and relax during motion. The result is muscles that are constantly pumping, eventually causing overdevelopment.
Prevalence and Treatment
No cure exists for Duchenne's and it is the most common and fatal form of muscular dystrophy. The overdeveloped muscles resulting from this disease might look strong but progressive weakness inevitably occurs from DMD. Treatments aim to help your child maintain as much mobility as possible despite the progression of the disease. Diagnostic testing of genetic mutations already occurring in families can help parents identify future risk for planned pregnancy. However, no means for preventing the mutation exists, as of the date of publication. Myotonia congenita affects 1 in 100,000 people worldwide, according to the Genetics Home Reference service of the U.S. National Library of Medicine. This condition is not fatal and treatment aims to improve muscle function. Research is ongoing to explore the mutations and cause of the gene abnormality in myotonia congenita.
References
- National Institute of Neurological Disorders and Stroke: Myotonia Congenita
- Genetics Home Reference: Myotonia Congenita
- Nephrongenic Diabetes Insipidus Foundation:Pseudohypertrophic Muscular Dystrophy
- American Academy of Orthopaedic Surgeons: Muscular Dystrophy
- Duchenne Muscular Dystrophy Research Fund: Duschenne Muscular Dystrophy
