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It's not just high-cost markets in California that would get squeezed by House Republicans' proposed $500,000 cap on the mortgage interest deduction.

Housing markets across cities in Louisiana, Nevada and Washington also have a significant percentage of loans over this threshold.

And in an ironic twist, the housing market in the Washington, D.C., metro area, where many U.S. government workers and elected officials live, would also be affected by the proposed limit.

Through the end of October, 5.4% of all mortgages closed nationwide (purchase and refinance) had a balance of over $500,000 at origination, according to Attom Data Solutions.

On a state level, Hawaii had the largest percentage of year-to-date 2017 originations over $500,000 at 15.1%, followed by California at 11.5% and Delaware at 9.3%.

It's not just the wealthy that take the mortgage interest deduction. Nearly 33.6 million taxpayers deducted $72.4 billion in mortgage interest from their 2014 taxes, and that figure could rise to as much as $96.4 billion by 2019, according to estimates from the Congressional Joint Committee on Taxation. Approximately 28 million filers — 83% — that claimed the home mortgage interest deduction on their tax returns in 2014 had household income under $200,000.

What's more, the GOP tax plan also calls for removing the deduction for state and local property taxes, which would further increase homeowners' tax obligation.

Here's a look at the 12 housing markets with the largest percentages of mortgages over $500,000. The data, from Attom, is based on metropolitan statistical areas with at least 2,500 closed loans in the first 10 months of the year.