Large study with twins highlights the limited role of genetics in mental health and the importance of effective early interventions for ADHD


Mul­ti­ple stud­ies have indi­cat­ed that, on aver­age, youth with ADHD have poor­er out­comes in young adult­hood in mul­ti­ple areas com­pared to their unaf­fect­ed peers.

A lim­i­ta­tion of these stud­ies, how­ev­er, is that they have not typ­i­cal­ly dis­tin­guished between indi­vid­u­als whose ADHD per­sists into adult­hood from those where the con­di­tion remits.

Youth whose ADHD remits may still expe­ri­ence adverse out­comes in young adult­hood rel­a­tive to oth­ers, per­haps because ear­ly dif­fi­cul­ties relat­ed to ADHD sets them on a neg­a­tive devel­op­men­tal path. Alter­na­tive­ly, neg­a­tive out­comes in young adult­hood may only be promi­nent among those whose ADHD persists.

Beyond this unre­solved issue, there are some indi­vid­u­als for whom exces­sive ADHD symp­toms emerge for the first time in young adult­hood. Although this pat­tern accounts for a large per­cent­age of adults with ele­vat­ed ADHD symp­topms, lit­tle is known about how their func­tion­ing com­pares to those with child­hood onset.

A study pub­lished recent­ly in the British Jour­nal of Psy­chi­a­try, ref­er­enced below, pro­vides a close look at how young adult out­comes in these groups compare.

2232 twins tracked for 10+ years

Par­tic­i­pants were a pop­u­la­tion cohort of 2232 twins born in Eng­land and Wales in 1994–1995. As part of a larg­er assess­ment, par­tic­i­pants were eval­u­at­ed for ADHD at ages 5, 7, 10, and 12. They were eval­u­at­ed again at age 18.

Results from these eval­u­a­tions were used to clas­si­fy par­tic­i­pants into one of four groups:

ADHD remit­ters (n=193) — ADHD diag­nosed dur­ing at least one of the child­hood assess­ments but not at age 18.

ADHD per­sis­ters (n=54) — ADHD diag­nosed dur­ing at least one of the child­hood assess­ments and also at age 18.

Late onset (n=112) — ADHD diag­nosed at age 18 but not earlier.

Com­par­i­son group (n= 1681) - ADHD nev­er diagnosed.

At age 18, indi­vid­u­als in these groups were com­pared on a vari­ety of out­comes includ­ing men­tal health, phys­i­cal health, sub­stance use, life sat­is­fac­tion, prob­lem­at­ic tech­nol­o­gy use, e.g., com­pul­sive inter­net use, edu­ca­tion, employ­ment sta­tus, and crim­i­nal convictions.

In mak­ing these com­par­isons, the researchers con­trolled for child­hood vari­ables that could con­tribute to group dif­fer­ences, includ­ing IQ, child­hood socioe­co­nom­ic status.


The role of famil­ial and genet­ic influ­ences — Because study par­tic­i­pants were all twins, and mem­bers of twin pairs often dif­fered on diag­nos­tic sta­tus, the authors could exam­ine how ADHD ver­sus genet­ic sim­i­lar­i­ty and shared fam­i­ly expe­ri­ence con­tributed to young adult outcomes.

Com­pared to their unaf­fect­ed co-twin, par­tic­i­pants with ADHD in either child­hood or adult­hood were more like­ly to expe­ri­ence depres­sion, anx­i­ety, sui­cide/­self-harm, low­er edu­ca­tion­al attain­ment and life-sat­is­fac­tion, and prob­lem­at­ic tech­nol­o­gy use.

These poor­er out­comes among par­tic­i­pants with ADHD are thus not due to genet­ic sim­i­lar­i­ties or shared fam­i­ly envi­ron­men­tal fac­tors, e.g., parental psy­chopathol­o­gy or fam­i­ly stress. Instead, they are more like­ly to reflect a con­se­quence of ADHD itself.

Life sat­is­fac­tion and prob­lem­at­ic tech­nol­o­gy use — Com­pared to those with­out ADHD, the remit­ted ADHD group showed mild­ly low­er life sat­is­fac­tion, while the per­sis­tent group had both low­er life sat­is­fac­tion and more prob­lem­at­ic tech­nol­o­gy use. The same was true for those in the late-onset ADHD group.

Men­tal health oucomes — ADHD remit­ters were no more like­ly than com­par­i­son sub­jects to be depressed (21.4% vs. 17.9%) or strug­gle with gen­er­al­ized anx­i­ety dis­or­der (6.4% vs. 5.8%) at age 18. They were, how­ev­er, more like­ly to be diag­nosed with con­duct dis­or­der (23.6% vs. 11.9%)

Rates of all 3 dis­or­ders were con­sid­er­ably high­er among ADHD per­sis­ters (35.2% for depres­sion, 24.1% for gen­er­al­ized anx­i­ety dis­or­der, and 38.5% for con­duct dis­or­der) and those in the late-onset group (42.9%, 16.1%, and 35.1%).

Edu­ca­tion and employ­ment — Edu­ca­tion­al out­comes were poor­er for all ADHD groups and espe­cial­ly low among those with per­sis­tent ADHD.

Indi­vid­u­als in all ADHD groups were also more like­ly to be out of both school and work com­pared to those with­out ADHD, and, to have high­er rates of crim­i­nal convictions.

Sub­stance use — Those with per­sis­tent and late-onset ADHD showed ele­vat­ed rates of cannabis (i.e, mar­i­jua­na) depen­dence and oth­er illic­it drug use rel­a­tive to those with­out ADHD or remit­ted ADHD.

Rates of cannabis depen­dence were 3.2%, 5.7%, 14.8% and 11.6% for com­par­i­son, remit­ters, per­sis­ters, and late-onset groups respec­tive­ly. For oth­er illic­it drug use, the rates were 15.5%, 21.8%, 29.6% and 30.4%.

Alco­hol depen­dence, in con­trast, was only high­er among late-onset sub­jects com­pared to the oth­er groups, who did not dif­fer from each other.

Phys­i­cal health out­comes - Those in the remit­ted and per­sis­tent groups were more like­ly to be obese as young adults com­pared to those who nev­er had ADHD. This was not true, how­ev­er, for late-onset individuals.

The risk of dai­ly cig­a­rette smok­ing was sim­i­lar­ly ele­vat­ed in all ADHD groups com­pared to those with­out ADHD.

Summary and implications

Over­all, results from this study con­firm pri­or research that chil­dren and adults with ADHD typ­i­cal­ly expe­ri­ence a range of neg­a­tive out­comes rel­a­tive to unaf­fect­ed peers.

How­ev­er, the nature and inten­si­ty of those neg­a­tive out­comes was found to vary by devel­op­men­tal pattern.

Indi­vid­u­als with child­hood ADHD that remit­ted were far­ing bet­ter in young adult­hood com­pared to oth­er ADHD groups as they were not at increased risk for either men­tal health prob­lems or illic­it drug use.

How­ev­er, they did show low­er edu­ca­tion­al attain­ment, increased risk of obe­si­ty, more fre­quent smok­ing, mild­ly low­er life sat­is­fac­tion, and high­er rates of crim­i­nal con­vic­tions than their unaf­fect­ed peers.

Those whose ADHD per­sist­ed expe­ri­enced not only expe­ri­enced these same neg­a­tive out­comes, gen­er­al­ly of greater mag­ni­tude, but also had poor­er men­tal health out­comes and were more like­ly to be involved in illic­it drug use. Sim­i­lar neg­a­tive out­comes were evi­dent among the late-onset group,

Over­all, even though out­comes are bet­ter when ADHD remits, some neg­a­tive con­se­quences in young adult­hood remain like­ly. And, when ADHD per­sists, the like­li­hood of mul­ti­ple neg­a­tive out­comes increases.

Final­ly, although cur­rent diag­nos­tic cri­te­ria require some impair­ment from ADHD symp­toms by age 12 for the diag­no­sis to be made, indi­vid­u­als whose symp­toms don’t emerge until adult­hood are also high­ly like­ly to strug­gle in mul­ti­ple areas. Clear­ly, these are indi­vid­u­als for whom clin­i­cal treat­ment is warranted.

While the above find­ings can inspire pes­simism, bet­ter out­comes for the remit­ter group high­lights the need for effec­tive ear­ly intervention.

And, it is espe­cial­ly impor­tant to high­light that not a sin­gle neg­a­tive out­come was expe­ri­enced by over 40% of indi­vid­u­als in any of the ADHD groups. In most cas­es, although neg­a­tive rates were high­er among the ADHD groups than in non­af­fect­ed indi­vid­u­als, they were often under 20% of the group.

Thus, rather than being cause for dis­cour­age­ment, these results high­light that although more youth with ADHD will strug­gle in young adult­hood com­pared to their unaf­fect­ed peers, the major­i­ty will not be sig­nif­i­cant­ly impaired as young adults in impor­tant domains of functioning.

An impor­tant pri­or­i­ty for future research is thus to iden­ti­fy which ADHD youth are most like­ly to have per­sis­tent strug­gles and what fac­tors best accounts for mean­ing­ful dif­fer­ences in young adult outcomes.

– Dr. David Rabin­er is a child clin­i­cal psy­chol­o­gist and Direc­tor of Under­grad­u­ate Stud­ies in the Depart­ment of Psy­chol­o­gy and Neu­ro­science at Duke Uni­ver­si­ty. He pub­lish­es the Atten­tion Research Update, an online newslet­ter that helps par­ents, pro­fes­sion­als, and edu­ca­tors keep up with the lat­est research on ADHD.

The Study:

Young adult men­tal health and func­tion­al out­comes in an 18-year prospec­tive cohort of twins (British Jour­nal of Psy­chi­a­try). From the abstract:

  • BACKGROUND: Atten­tion-deficit hyper­ac­tiv­i­ty dis­or­der (ADHD) is asso­ci­at­ed with men­tal health prob­lems and func­tion­al impair­ment across many domains. How­ev­er, how the lon­gi­tu­di­nal course of ADHD affects lat­er func­tion­ing remains unclear.
  • AIMS: We aimed to dis­en­tan­gle how ADHD devel­op­men­tal pat­terns are asso­ci­at­ed with young adult functioning.
  • METHOD: The Envi­ron­men­tal Risk (E‑Risk) Lon­gi­tu­di­nal Twin Study is a pop­u­la­tion-based cohort of 2232 twins born in Eng­land and Wales in 1994–1995. We assessed ADHD in child­hood at ages 5, 7, 10 and 12 years and in young adult­hood at age 18 years. We exam­ined three devel­op­men­tal pat­terns of ADHD from child­hood to young adult­hood — remit­ted, per­sis­tent and late-onset ADHD — and com­pared these groups with one anoth­er and with non-ADHD con­trols on func­tion­ing at age 18 years. We addi­tion­al­ly test­ed whether group dif­fer­ences were attrib­ut­able to child­hood IQ, child­hood con­duct dis­or­der or famil­ial fac­tors shared between twins.
  • RESULTS: Com­pared with indi­vid­u­als with­out ADHD, those with remit­ted ADHD showed poor­er phys­i­cal health and socioe­co­nom­ic out­comes in young adult­hood. Indi­vid­u­als with per­sis­tent or late-onset ADHD showed poor­er func­tion­ing across all domains, includ­ing men­tal health, sub­stance mis­use, psy­choso­cial, phys­i­cal health and socioe­co­nom­ic out­comes. Over­all, these asso­ci­a­tions were not explained by child­hood IQ, child­hood con­duct dis­or­der or shared famil­ial factors.
  • CONCLUSIONS: Long-term asso­ci­a­tions of child­hood ADHD with adverse phys­i­cal health and socioe­co­nom­ic out­comes under­score the need for ear­ly inter­ven­tion. Young adult ADHD showed stronger asso­ci­a­tions with poor­er men­tal health, sub­stance mis­use and psy­choso­cial out­comes, empha­sis­ing the impor­tance of iden­ti­fy­ing and treat­ing adults with ADHD.

The Study in Context:

About SharpBrains

SHARPBRAINS is an independent think-tank and consulting firm providing services at the frontier of applied neuroscience, health, leadership and innovation.
SHARPBRAINS es un think-tank y consultoría independiente proporcionando servicios para la neurociencia aplicada, salud, liderazgo e innovación.

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