Not particularly further. The difference is more a symptom than a cause. It typically reflects prolonged restrictions in access to text that are discordant with an individual's actual verbal intelligence. For young children, most vocabulary and general knowledge comes from oral sources. When reading becomes the principal source of these verbal knowledge skills (as in older students, or in early readers with high verbal cognition), relative delays in reading skill can cause the measures of verbal reasoning and verbal knowledge to start diverging. The longer the restriction in access to text exists, the greater the divergence.
In your DS's case, we already have an explanation for the restriction in access to text. Once that is resolved or accommodated, the expectation would be that, after a period of catch up reading, the knowledge gap would begin closing gradually, and probably mostly dissipate within a few years. If he continues to find reading laborious, you can also compensate to some extent with rich, high-level audiotexts.
