While reviewing applicants for a position, I noticed a disclosure in a letter of recommendation that is potentially unethical. I'm sure this happens from time to time - something like "Jane Doe's contributions are especially impressive because her husband is constantly busy working at a hedge fund and she has small three children, two of whom have cystic fibrosis". On the one hand, that does put her work in context and make it more impressive in some respects. However, if there are no hedge funds near my university or the local medical system isn't well developed to treat such a complicated condition, it'd be hard not to let that disclosure influence my or my department's thinking. Sometimes these disclosures are intentional, but I don't believe the one I noticed (which is not the scenario outlined above) is.
My first reaction is that I should take the disclosure as a positive if it is in fact a positive (maybe we have lots of hedge funds nearby and a cystic fibrosis research center, so Jane would consider stooping down to our department's level!) and try to ignore it if it is a negative. On the other hand, perhaps it would be best to check directly with the writer and ask what they intended by making a disclosure. If the disclosure is unintentional, this gives the writer a chance to update their letter.
Clearly, the approach taken should vary depending on the details of the case, but are there other options I'm not considering?