Mutations in the same gene causing phenotypically different motor neuron diseases
Selected genetic forms of motor neuron diseases offer examples of allelic disorders with overlapping phenotypes.
For instance, mutations in the ALS2 gene have been reported in juvenile amyotrophic lateral sclerosis (ALS), infantile-onset ascending hereditary spastic paralysis, and in familial juvenile primary lateral sclerosis.
Mutations in the VAPB gene have been identified in ALS8 and in late-onset SMA.
This phenotypic variability is not limited to motor neuron diseases and can present a significant diagnostic challenge, especially in very rare disorders.