Also known as Werdnig-Hoffmann disease is the most common form of all. Its severe form can be seen at birth or within the first few months. Children affected cannot control their head movements. Others may struggle sitting down without any assistance. Others may have difficulty swallowing, which often lead to difficulty feeding. Some may also develop breathing problems because of the weakness of their respiratory muscles. Due to respiratory failure, most patients who suffer from this type of condition do not survive past early childhood. 