Many books on Ottoman history mention the custom of confining male relatives of the ruling sultan in kafes or so-called "Golden Cages" for life. Some books also claim that during the later years of the Empire, the confinement became so severe that some princes went insane or had serious problems with social interaction. For example, the hugely entertaining Lords of the Horizons by Jason Goodwin claims that some princes didn't even learn to talk.
I know Goodwin's book isn't an academic source, so how much truth is there in these stories of sensory deprivation and solitary confinement? I've understood that princes usually spent their childhood in the lively imperial harem before being removed to the kafes at the onset of puberty, so surely they would have acquired at least rudimentary social skills? Do we have any records of insane or mute princes in these circumstances?
EDIT: Typo
The kafes really was a thing; the "Golden Cages" were a number of apartments in the Fourth Courtyard of the Topkapı Palace. I don't know of any mute princes, but there's definitely an assortment of insane ones. Perhaps the most famous was Sultan Ibrahim I, a fine example of an Ottoman prince who was damaged mentally by his long imprisonment in his "Golden Cage"; his behavior was bizarre enough to posthumously earn him the epithet "the Mad". To quote a passage assessing his character in Patrick Kinross's The Ottoman Centuries:
Reared exclusively in the Seraglio, in virtual imprisonment and often in fear, Ibrahim was a weakling who had inherited [Ahmed I]'s vice of cruelty but none of his virtues. An irresponsible voluptuary, fitful in temper, unscrupulous in character, and avaricious in spirit, he was ruled by his harem and by his frivolous moods and desires.
Some examples of Ibrahim's unsultanly actions:
• Authorizing his harem favorites to take whatever they wanted from the bazaar without payment
• Attempting to decorate the entire seraglio with sable skins (Ibrahim was obsessed with furs and scents, to the extent that he established taxes on those two classes of goods with the intent of having them paid in kind).
• Searching for the fattest woman in the empire; upon finding her, he made her Governor-General of Damascus. (EDIT: The Hark! a Vagrant comic entitled The Decline of the Ottomans Begins Now references this episode)
Sources: The Ottoman Centuries by Lord Kinross, for information on Ibrahim and his reign
The Decline and Fall of the Ottoman Empire by Alan Palmer, for what scant information on the kafes I could find