Distressed Pear tree

[Charl&Pete]

One of my pear trees has suddenly lost it's leaves. The fruits remain (though are small) and I can't see any signs of damage to the trunk or the branches, although there hasn't been much new growth this year.
Any ideas? Should I get rid of it in case it affects the other pear trees?

[Mert]

Our pear tree continues to have branches that just die off. The pears look healthy. The tree is very overgrown and has not had any pruning in years. We have started pruning but we are concerned how much and is it real y good for the tree.