Child and Adolescent Psychiatry

278 Chapter 33

classified as receiving better rearing. Any risk transmitted from adoptive
parents was probably mediated by psychosocial factors.
Box 33.2 illustrates how high and low congenital risk interacted with
better and worse rearing:

Among adoptees experiencing better rearing, high congenital risk was
linked to four times the rate of convictions, 12% versus 3%, suggesting
a considerable biological effect.
Among adoptees at low congenital risk, worse rearing more than dou-
bling the rate of convictions from 3% to 7%, suggesting a substantial
effect for psychosocial environment.
The really striking finding was that when adoptees at high risk also
experienced worse rearing, the conviction rate soared from 12% to
40%. This shows a strong interaction whereby increased biological risk
leads to a far poorer outcome when combined with a less favourable
environment. Or to put it another way, the effect of an adverse envi-
ronmental influence is greater when combined with genetic (or other
biological) susceptibility.
Paradoxically, the strong interaction between biological and environ-
mental risk justifies some therapeutic optimism. This is because the
adoptees with the double disadvantage of high congenital risk and worse
rearing environment have the most to gain from intervention – potentially
dropping their conviction rate in this instance from 40% to 12% if their
adoptive parents can be helped to improve their child rearing. Far from
being ‘heartsink cases’ for whom nothing can be done, they may be
particularly dramatic responders.
In general, genetic liability can translate into poorer outcomes through
several mechanisms. First, it may directly lead to psychopathology

Box 33.2Interaction between biological and social risk: conviction

rates for teenage adoptees according to risk status of biological

and adoptive parents (based on data from Bohman, 1996)

%

Criminality

50

40

30

20

10

0

Better rearing Worse rearing

Low congenital risk

High congenital risk