More former players have joined the legal process against the game’s authorities for alleged negligence.
Former Wales Under-20 centre Adam Hughes, 30, is the youngest to claim he has suffered permanent brain damage.
Ex-England Under-21 back row Neil Spence is also one of those involved while four former England and Wales players remain anonymous.
Legal action is being prepared against the Rugby Football Union (RFU), Wales Rugby Union (WRU) and World Rugby.
It means there are now nine players included in preparing the action – although the law firm representing the group says more than 100 players have come forward.
Those additional players will now be tested for early onset dementia and their details added to the potential claim involving the existing nine when it is ready.
A letter of claim, setting out their intention to sue, was delivered to the governing bodies on Thursday.
In response, the RFU, WRU and World Rugby have issued a joint statement to confirm they have received the letter, and are “deeply saddened” to hear personal accounts from the players.
They also say player welfare is taken “extremely seriously” and it “continues to be our number one priority”.
World Rugby chairman and former England captain Sir Bill Beaumont said in an open letter his “thoughts are with” those who are struggling and that the organisation will “continue to welcome” the views of former players.
He added the area of concussion is “extremely complex” but that as “the science continues to evolve” rugby will “evolve with it”.
Every member of the group of nine, including England’s World Cup-winning hooker Steve Thompson, has recently been diagnosed with early signs of dementia.
The former players say repeated blows to the head are to blame.
Spence says he used to be “the fun guy at the party” but that his condition has “taken my personality”.
“If I knew I was going to feel like this I wouldn’t have signed up,” Spence told BBC Sport.
“We knew we were signing up to broken arms, broken legs and knee replacements, but not being neurologically impaired and a degenerative disease.
“I still love the game, and what we are trying to get from this is ideally some change. The change should be potentially limiting some contact during the training.”
Meanwhile, 42-year-old Thompson played in every England match when they won the 2003 World Cup, but says: “I can’t remember any of those games. It’s frightening.”
It is the first legal move of its kind in world rugby and, if successful, could change the way the game is played.
Rylands Law, which is representing the group, says the risks of concussion injuries were “known and foreseeable”, and list 24 alleged failures on the part of World Rugby, the RFU and the WRU.
“We know senior figures in the game have been discussing the issue of head injuries since the 1970s, and yet here we are, more than 40 years later, with so many players, and at such an early stage in their lives, finding themselves in this awful position,” said Richard Boardman of Rylands Law.
“I sincerely hope World Rugby, RFU and WRU will now face up to their responsibilities.”
‘The human body is the same the world over’
Meanwhile NFL medical experts say they are in regular communication with rugby authorities about how to reduce concussion in the sport.
NFL chief medical officer Dr Allen Sills says his sport is trying to “share knowledge in a more rapid fashion” with World Rugby and other contact sports.
“We do share regularly with each others sporting groups across the world,” Sills told the BBC.
“If there are silver linings with the Covid-19 situation, I would say that this has strengthened our communication further.”
Sills says there are some differences with technique and training between American football and rugby union, but admits the internal damage can be similar because “the human body is the same the world over”.
“We talk at least every couple of weeks with World Rugby, Australian Football, and a number of these other contact sports, and we’re sharing the learnings that we have,” he added.
“We share what we’re finding in our research, we share what our rules changes are and we’re learning from each other and I think we all share the same goal.”
What is CTE & how can it be diagnosed?
Each player to have come forward so far has been diagnosed by neurologists at King’s College London with early onset dementia and probable Chronic Traumatic Encephalopathy (CTE).
CTE is the disease discovered by Dr Bennet Omalu in American football player Mike Webster, and the subject of the film Concussion starring Will Smith. In 2011, a group of former American football players started a class action against the NFL and won a settlement worth about $1bn (£700m).
CTE can develop when the brain is subjected to numerous small blows or rapid movements – sometimes known as sub-concussions – and is associated with symptoms such as memory loss, depression and progressive dementia.