Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Example Input: Context: In the county, the population was spread out with 23.5% under the age of 18, 7.8% from 18 to 24, 28.5% from 25 to 44, 25.9% from 45 to 64, and 14.2% who were 65 years of age or older. The median age was 40 years. For every 100 females, there were 93.8 males. For every 100 females age 18 and over, there were 90.5 males. 
 Question: Which age group had the third most people?
Example Output: under the age of 18

Example Input: Context: This article's plot summary may be too long or excessively detailed. Please help improve it by removing unnecessary details and making it more concise. (October 2011) (Learn how and when to remove this template message) Oyuki, a tattooed female assassin the renegade member of a daimyo's personal bodyguard detail is killing every man that is sent up against her. Along with her deadly use of the short blade, she strips to the waist while fighting to reveal elaborate tattoos on her chest and back. On her front is a kintaro grasping her left breast. A portrait of a mountain witch covers her back. She then cuts off her victims' topknots, or chonmage, which brings dishonor to the dead man and his family. Ogami Itto, the disgraced former shogun's executioner, or Kogi Kaishakunin, is hired to kill Oyuki. He tracks down the tattoo artist, who explains that she was a "fine" woman who did not scream as he dug into her flesh with his needles. Meanwhile, Itto's 3-year-old son, Daigoro, has grown restless waiting by the baby cart his father uses to trundle him about in. He goes exploring and finds a pair of performing clowns on the street. When the clowns finish their performance, Daigoro follows them, hoping to see more. But the clowns shoo him away, saying it's time to go home. Now, Daigoro has wandered too far. He is lost, and has become separated from his father. Agents of the Ogamis' mortal enemies, the Yagyu, are never far away. A procession of them, accompanied by the sound of gongs and loud shrieks, sends Daigoro into hiding. Itto must give up his search rather than risk an entanglement with the men, so he travels on alone. Daigoro spends days looking for his father, searching in every temple in the countryside. He enters one temple and sees a figure at the altar praying, but it is not his father. Rather, it is a man whom Daigoro immediately recognizes as someone who is unfriendly. The man follows Daigoro, who wanders into a grass field as it is being lit on fire by farmers. Unwittingly, Daigoro is surrounded by the flames, but he proves his resourcefulness by burying himself and surviving. The man then turns his sword on Daigoro, who raises a stick to defend himself, and in that instant the man realizes who Daigoro is. Just then, Itto comes into the picture, and the two recognize each other. The man, it turns out is Gunbei Yagyu, the outcast son of Retsudo Yagyu. Gunbei and Itto had competed for the post of shogun's executioner, and Gunbei's fierce swordsmanship surely would have won him the post, but in his over zealousness, he ends up pointing his sword at the shogun a taboo movement that costs him the job and makes him an outcast. Itto and Gunbei now have a rematch, but Itto is much improved and is ready for Gunbei. With a swift stroke, he chops off Gunbei's right arm. Gunbei then begs Itto to kill him, but Itto refuses, saying there is nothing to be gained from slaying a man who is already dead. With Gunbei out of the way and father and son reunited, the action then turns on finding the tattooed killer, Oyuki. He first stops at a settlement of street actors that Oyuki was said to be a part of. He talks to the elder and hears more of her story, and it happens that the elder is Oyuki's father, who is opposed to her actions, and cooperates with Itto. Itto finally locates Oyuki at a hot spring and witnesses her in action against more vassals who have come to try to kill her. Then her nemesis, her former instructor who raped her and set her on her bloody vendetta, shows up with his flaming sword and blazing eyes. But she is no longer in his sway, and when he sees her tattoos, he is distracted and killed. Finally, Itto and Oyuki must duel, and he makes quick work of her. She dies a splendid 
 Question: Of what is the portrait that covers her back?
Example Output: a mountain

Example Input: Context: Christianson syndrome (OMIM 300243), caused by mutations in the X-linked SLC9A6 gene, is characterized by severe global developmental delay and intellectual disability, developmental regression, epilepsy, microcephaly and impaired ocular movements. It shares many common features with Angelman syndrome. Carrier females have been described as having learning difficulties with mild to moderate intellectual disability, behavioural issues and psychiatric illnesses. There is little literature on the carrier female phenotype of Christianson syndrome. We describe a large extended family with three affected males, four carrier females, one presumed carrier female and one obligate carrier female with a c.190G>T, p.E64X mutation known to cause a premature stop codon in SLC9A6. We characterize and expand the clinical phenotype of female SLC9A6 mutation carriers by comparing our described family with female carriers previously discussed in the literature. In particular, we highlight the neurodevelopmental and psychiatric phenotypes observed in our family and previous reports. 
 Question: Mutation of which gene is implicated in the Christianson syndrome?
Example Output:
slc9a6