Cerebral Palsy is a thing, and Asher and Nolan have it. The end.
Not a good enough explanation? Well it really is that simple because there's lots of things to know about Asher and Nolan, and Cerebral Palsy is just one of them. But I suppose I can do better than that.
Cerebral Palsy is defined as*:
A group of disorders affecting body movement and muscle co-ordination. The medical definition of CP is "a non-progressive but not unchanging disorder of movement and/or posture, due to an insult to or anomaly of the developing brain".
Cerebral = of the brain
Palsy = lack of muscle control
We know Asher suffered a brain hemorrhage between days one and four of life, but we are unsure of when Nolan's injury occurred - likely in the same general timeframe but it was not obvious on head ultrasounds like Asher's was. Neither of the boys has had an MRI to locate the exact area of injury because, really, does it matter where or how it happened? They were more than three months premature, and it happened. (And also, we tried, but Asher stopped breathing with the sedation, so clearly he thought it wasn't very important either).
Asher has a more uncommon type called "athetoid" or "dyskinetic", meaning he has uncontrolled movements and more low muscle tone (hypotonia) than high (spasticity). All four of Asher's limbs are affected, as is his trunk, so he is considered quadriplegic. Asher cannot stand or walk unassisted, and is just learning to sit independently for a few seconds at a time, but has a whole ton of fancy equipment to help him do all of the above. Equipment aside, the most important weapon in Asher's artillery is his charm. Look out ladies (or gents - whoever he's in to).
Nolan's original diagnosis was "spastic diplegia", meaning his lower body is affected by spasticity, or tightness; however, in recent months it's been questioned whether he is actually more affected by hypotonia in his feet, in addition to a small bit of spasticity in his legs and hips. Nolan's CP is considered very mild and was only diagnosed when he walked later, and with more clumsiness, than his peers. Nolan's other fine and gross motor skills are all typical, and every day he is learning to walk and run more steadily.
*From the BC Cerebral Palsy Association website