Initial capitalization of foreign surnames when starting a sentence

Fortunately, The Chicago Manual of Style (16th edition) deals with this question on page 388:

8.5 Names with particles. Many names include particles such as de, d', de la, von, van, and ten. Practice with regard to capitalization and spacing the particles varies widely, and confirmation should be sought in a biographical dictionary or other authoritative source. When the surname is used alone, the particle is usually retained, capitalized or lowercased and spaced as in the full name (though always capitalized when beginning a sentence). [emphasis added]

So, following Chicago, the correct sentence is, "De Bernezan entered the room."

The variation in capitalization you found on the De Vries Wikipedia page is explained by the Chicago rule for Dutch names used in an English context (page 390):

8.10 Dutch names. In English usage, the particles van, van den, ter, and the like are lowercased when full names are given but usually capitalized when only the last name is used.

Johannes van Keulen; Van Keulen

Pieter van den Keere; Van den Keere

Vincent van Gogh; Van Gogh

Gerard ter Borch; Ter Borch

The case of a reference list of an academic paper will be covered in my answer. (Sorry, not directly relevant to the OP, but this question is redirected here.)

APA Style says, according to APA Style Blog: How to Capitalize Author Names in APA Style, in a reference list, lowercase is retained:

de Haan, A. D., Deković, M., & Prinzie, P. (2012). Longitudinal impact of parental and adolescent personality on parenting. Journal of Personality and Social Psychology, 102, 189–199. doi:10.1037/a0025254

APA Style agrees with the Chicago Manual for the sentence beginning. After a colon capitalization is necessary, too. Thus:

• De Haan, Deković, and Prinzie (2012) studied the impact of parental and adolescent personality on parenting.
• Recently, researchers have explored the impact of personality on parenting: De Haan, Deković, and Prinzie (2012) used longitudinal analyses to untangle the effects.

The capitalization rule for Dutch surnames is given here on the website of the Nederlandse Taalunie (the Dutch-Belgian authority for matters orthographic). This is in Dutch but one can translate it with the translation facility in Google (right-click on the page and select the translation option).

The general rule is that surnames are given a capital initial letter. An important exception is that if the surname starts with a preposition ("van") or an article ("de"), and is preceded by a given name, an initial, or another family name, it is not capitalized. This is a source of much confusion in Anglophone circles. Example: Piet de Haan is a member of the De Haan family.