Pain experience of children with Christianson syndrome

Abstract

Children with Christianson syndrome (CS), an X-linked neurodevelopmental disorder caused by loss-of-function mutations in the alkali cation/proton exchanger SLC9A6/NHE6, display severe cognitive impairments, mutism, and sensory abnormalities such as hyposensitivity to pain. However, it is unclear whether these children display other sensory abnormalities and whether their pain hyposensitivity is the result of an elevated pain threshold or a complete insensitivity to pain. To better characterize the sensory abnormalities in this disorder, we used a combination of a mouse model of CS and pain questionnaires directed at nonverbal patients with CS. We recruited 14 young male participants with CS and subjected them to a novel observational tool, the Pain Sensory and Painful Situations Questionnaire (PSQ), which takes multiple painful situations into account to broaden the description of pain expression. By analyzing social expressive behaviours of pain in these nonverbal patients, the PSQ documented that over 60% of the participants were unaffected by mechanical or inflammatory painful stimuli. This reduced pain sensitivity was also observed in the mouse CS model. Surprisingly, CS mice also displayed aversive reactions to innocuous stimuli, which prompted us to examine whether such reactions were also present in children with CS. Indeed, the results from the PSQ revealed that 30% to 50% of these patients showed an aversive response to normally innocuous stimuli like light touch and gusts of air. Our results demonstrate that children with CS have aversive reactions to innocuous stimuli and are hyposensitive to painful stimuli, the latter making them at risk for developing complications from unreported injuries.

Keywords: Children; Christianson syndrome; Pain; Touch aversion.

Figure 1.

NHE6 and SLC9A6 expression in human DRGs and behavioural tests with Slc9a6 KO mice and their WT littermates. (A) Representative images of DRGs stained with NHE6 antibody and DAPI. (B) Percentage distribution of the cross-sectional area (CSA) of NHE6 positive neurons. (C) Representative images of DRGs stained for the mRNAs of SLC9A6 and P2RX3 and percentage of P2RX3-, SLC9A6-, and P2RX3-SLC9A6-positive neurons assessed (lower right inset). (D) Percentage distribution of the CSA of P2RX3-, SLC9A6-, and P2RX3-SLC9A6-positive neurons. (E) Western blot for NHE6 expression between Slc9a6 WT, HET and KO mice DRGs, and human DRGs. (F) Mean ± standard error paw withdrawal latency measured in the radiant heat assay in Slc9a6 KO (n = 10) and WT (n = 10) mice. ***P < 0.001, Student t test. (G) Number of nocifensive bouts observed in WT (n = 10) and Slc9a6 KO (n = 9) mice in response to plantar application of mustard oil (AITC). *P < 0.05, Student t test. (H) Distribution (%) of behavioural responses to plantar stimulation in the dynamic brush assay in WT (n = 10) and Slc9a6 KO (n = 10) mice. ****P < 0.0001, χ² test. Red, nocifensive response. Blue, Withdrawal response. White, No response. DAPI, 4′,6-diamidino-2-phenylindole; DRG, dorsal root ganglia; KO, knockout; NHE6, (Na+, K+)/H+ Exchanger 6; WT, wild-type.

Figure 2.

Rate types for each item of the PPP questionnaire in the cohort (n = 14) during (A) a “good day” or during (B) their most troublesome pain. Item 1: Is cheerful; Item 2: Is sociable or responsive; Item 3: Appears withdrawn or depressed; Item 4: Cries/moans/groans/screams or whimpers; Item 5: Is hard to console or comfort; Item 6: Self-harms, eg, biting self or banging head; Item 7: Is reluctant to eat/difficult to feed; Item 8: Has disturbed sleep; Item 9: Grimaces/screws up face/screws up eyes; Item 10: Frowns/has furrowed brow/looks worried; Item 11: Looks frightened (with eyes wide open); Item 12: Grinds teeth or makes mouthing movements; Item 13: Is restless/agitated or distressed; Item 14: Tenses/stiffens or spasms; Item 15: Flexes inwards or draws legs up towards chest; Item 16: Tends to touch or rub particular areas; Item 17: Resists being moved; Item 18: Pulls away or flinches when touched; Item 19: Twists and turns/tosses head/writhes or arches back; Item 20: Has involuntary or stereotypical movements/is jumpy/startles or has seizures. PPP, pediatric pain profile.

Figure 3.

Rate types for each item of the NCCPC-R questionnaire in cohort (n = 14) ordered according to frequency of item occurrence. Item 15: Jumping around, agitated, fidgety; Item 7: Seeking comfort or physical closeness; Item 9: A furrowed brow; Item 28: Eating less, not interested in food; Item 1: Moaning, whining, whimpering; Item 8: Being difficult to distract, not able to satisfy or pacify; Item 5: Not cooperating, cranky, irritable, unhappy; Item 6: Less interaction with others, withdrawn; Item 10: A change in eyes; Item 3: Screaming/yelling; Item 14: Not moving, less active, quiet; Item 17: Stiff, spastic, tense rigid; Item 11: Turning down of mouth, not smiling; Item 22: Shivering; Item 30: Decrease in sleep; Item 16: Floppy; Item 20: Flinching or moving the body part away, being sensitive to touch; Item 4: A specific sound or word for pain; Item 12: Lips puckering up, tight, pouting, or quivering; Item 13: Clenching or grinding teeth, chewing or thrusting tongue out; Item 19: Protecting, favoring, or guarding part of the body that hurts; Item 21: Moving the body in a specific way to show pain; Item 26: Sharp intake of breath, gasping; Item 24: Sweating, perspiring; Item 29: Increase in sleep; Item 2: Crying; Item 18: Gesturing to or touching part of body that hurts; Item 23: Change in color, pallor; Item 25: Tears; Item 27: Breath holding. NCCPC-R, noncommunicative children pain checklist-revised.

Figure 4.

Responses to the pain sensory and painful situations questionnaire (PSQ). (A) Distribution of increased sensitivity or aversive reactions to different stimuli. (B) Distribution of participants that retained sensitivity during different painful situations.