Primrose's pups at 4 weeks old

Primrose's Brittany/Cavalier pups are now 4 weeks old and I'm going to start to have to make decisions about these pups. Firstly, I have had to decide if I am going to keep one back. Losing one of the pups having Congenital hydrocephalus which not that much is known about, but is thought to have an hereditary factor, my first feeling after putting Tiddler to sleep was I really would not wish to go through that experience again, but I let the dust settle and did a lot more further searching through of information about hydrocephalus and with no history that I know of in the recent ancestry of both parent dogs, I'm edging on the side of taking the risk and keeping a puppy back. 
The fact is we all carry lethal genes, it is thought around on average at least four sets, which is most probably around the same for dogs and obviously the closer we are related to each other when breeding the more likelihood of those lethal genes being expressed. Because when closely related the chances are much higher that you will be carrying an identical set of lethal genes. See it ain't rocket science, the roulette wheel of breeding, but try getting a pure breeder evangelist  to understand the statistical chances of closely related animals are more likely to express hereditary illnesses in their offspring than distantly related animals is like sitting in a dark room banging your head against the wall. 
Breeding is a numbers game and with all the health testing in the world and crossbreeding, every now and again you will get something that was unexpected. When you have livestock, you will invariably end up with dead stock, as we say in farming. The thing with hydrocephalus is it could be just a mutation at conception or hereditary. With Primrose being a Cavalier hereditary factors are a high probability and Henry being from a breed with the bobtail gene in it which can express itself as Spina bifida which is thought to have an association with hydrocephalus, just maybe Primrose and Henry had that unlucky set of matching lethal genes to express hydrocephalus in one of their offspring. If this was the case it means there is a chance that the other offspring are now carries of one set of the lethal gene, but there is also a chance that only one puppy was unlucky enough to be past on the genes and that was the pup that presented with the condition. 
I'm going to edge on the reasoning that the pups potentially are carries (By carries I mean they have a chance of carrying one set of the genes for hydrocephalus. They won't get the condition, but if mated with another carrier it could be expressed in their offspring) , so that means I would not keep a male back to reduce genetic spreading if a carrier, but as I will hopefully use the offspring with a dog that is 3/4 Cavalier 1/4 Poodle and know for sure in three generations of his breeding no pups have been born with hydrocephalus, the risk factor for me is low enough to retain a bitch from Primrose's litter and hope to breed a litter from in the future. Maybe a gene test might even be available by then.
Tough choices and a bit of sentimentality. I think Primrose deserves the chance to keep one of her offspring. Watching the dynamics in our pack over the years, it is obvious that if birth bonds are not broken, they stay tied.