Anyone from a small community has had this thought, and most families have had the conversation awkwardly and then dropped it.
It deserves better than that, because the fear is often larger than the reality and the caution is worth keeping anyway.
What the actual risk is
Anglo-Indian families in a given city have frequently intermarried for generations, so distant connection is common. Second and third cousins are not unusual.
What matters medically is close consanguinity — first cousins, or closer. Distant relation, several generations back, is not the same thing and is common in every small community on earth.
Most of what people worry about here is the first case, and most of what they actually encounter is the second.
How to check without making it strange
Ask about grandparents. Not "are we related" — names, places, parishes. Where the grandparents were from, which school, which railway division, which church.
Anglo-Indian families are unusually good at this. Two people comparing four surnames and three towns will usually establish in ten minutes whether there is a connection, and it feels like conversation rather than an audit.
When a connection turns up
It usually turns out to be further away than it first sounded — a shared great-grandparent, or two families from the same parish who were never actually related.
If it is genuinely close, a doctor is the right person to ask, not an uncle. The medical question has an actual answer and it varies by relationship.
The part that gets forgotten
This is a strong argument for looking beyond your own city.
Families who search only locally find the same handful of names and the same tangled connections. Families willing to look at Chennai, Kolkata, Bangalore or abroad find people with no connection at all — which solves this concern completely, and several others at the same time.
The narrower the search, the more likely you are to run into your own family tree. Widening it is not just about having more options; it is the direct answer to this particular worry.