Physicians encountering children with hypotonia and weakness should maintain a high index of
suspicion for the diagnosis of SMA. Certain physical characteristics are readily identifiable. The
weakness is usually symmetrical and more proximal than distal. Sensation is preserved. Tendon
reflexes are absent or diminished. Weakness in the legs is greater than in the arms. The severity of
weakness generally correlates with the age of onset. Classification and typical clinical features of SMA
are listed in Table 1. Apart from these, Type IV SMA is also referred to. This is a mild form that presents
in adult age. Some patients will manifest features that are at the margins between groups.