Growing pains, a prevalent, idiopathic condition with disordered somatosensory processing, is genetically influenced

Shanthi Pathirana, G. David Champion, Tiina Jaaniste, Anthony Yee, Rani Sachdev

Sydney Children's Hospital, Sydney, Australia

Background: We addressed deficiencies in knowledge of causal and pathogenetic mechanisms of the prevalent familial childhood disorder growing pains (GP).

Methods: Thirty-three cases (5-12 years), fulfilling validated criteria for GP, were recruited through the media. Control participants (n=29), who did not have limb pains, were 19 siblings of cases and 10 unrelated children. Evidence for peripheral neuropathic disorder was sought by questionnaire, sensory testing, and neurological examination. The principal investigator, unaware as to case or control status, obtained quantitative somatosensory responses from limbs and abdomen to ethically approved cutaneous and deep stimuli. The hypothesis that the familial occurrence of GP is significantly explained by genetic factors was tested by determining concordance rates in monozygous (MZ) and dizygous (DZ) twins recruited from the Australian Twin Registry. A total of 943 registered families with twins aged 3-12.9 years (309 MZ, 634 DZ) living in NSW were surveyed by mail.

Results: The cases and control groups were comparable on demographic criteria. There were statistically significant (p< 0.05) increased responses to cutaneous cold, deep pressure, and vibration averaged over all sites in the cases compared to the controls. We found no evidence that GP is a peripheral neuopathic pain syndrome.
In the twins surveyed, the response rate was 40%. The overall response rate for families with at least one child with GP was 11%. Of these there were 24 MZ twin pairs, 17 (71%) of which were concordant. Of the 24 DZ twin pairs, 2 (8%) were concordant. The Holzingers heritability estimate was 0.68 and Allen's heritability was 0.89.

Conclusion: GP is genetically influenced and involves centrally mediated disorder of somatosensory processing. It shares many characteristics with the conditions that have been grouped as idiopathic pain disorders or central sensitivity syndrome.