There are two issues here
- Are Jews permitted to test for genetic diseases before getting married? Are they required to?
- Does this apply differently for Ashkenazim and Sefardim?
The answer to the first issue is that it is permitted and even recommended by some for Ashkenazim because of the prevalence and terrible consequences of Tay-Sachs. See for instance
- R Moshe Feinstein and R Tendler views here
- R J. David Bleich here (as well as a mention of Dor Yeshorim who tests according to R Moshe's psak)
- Nishmat here
- a very complete article by Dr Fred Rosner, the Jewish medical ethicist,there
On the second, I had looked into this before getting married. Since I am Ashkenazi and my wife is Sefardi, Tay-Sachs doesn't apply and I decided not to test further as the frequency of other genetic diseases is much lower than other risks you accept when having kids (e.g, Dow).
Of course you should CYLOR for your specific situation and not rely on stranger's opinions even if they are well-intended and writing on respected sites.