ได้รับค่าพยากรณ์ที่ จำกัด Given the limited positive predictive value of both genetic and
ในเชิงบวกของทั้งสองทางพันธุกรรมและปัจจัยความเสี่ยงด้านสิ่งแวดล้อมสำหรับการวินิจฉัยในภายหลังของโรคจิตเภทการศึกษาที่ผ่านมาได้มุ่งเน้นไปที่วิธีการอื่นenvironmental risk factors for the later diagnosis of schizophrenia,
ๆ recent studies have focused on other methods for detecting individuals
ในการตรวจสอบบุคคลที่มีความเสี่ยงสูงสำหรับการแปลงเป็นโรคจิต ยกตัวอย่างเช่นใน treatmentseeking at high risk for conversion to psychosis. For example, in treatmentseeking
กับบุคคลที่มีอาการ prodromal individuals with prodromal symptoms of schizophrenia, about
ของโรคจิตเภทประมาณหนึ่งในสามจะแปลงเป็นโรคจิตในช่วงหลายปีข้างหน้า. one-third will convert to psychosis over the next several years.
แต่ประมาณสองในสามของบุคคลที่กำลังมองหาการรักษาที่มีสองคนหรือมากกว่าของลักษณะบางอย่าง (เช่นความเสี่ยงทางพันธุกรรมด้วย ที่ผ่านมาการเสื่อมสภาพในการทำงานระดับสูงของเนื้อหาความคิดที่ผิดปกติหรือหวาดระแวงการด้อยค่าทางสังคมหรือประวัติศาสตร์ของการใช้สารเสพติด) จะแปลง(แคนนอน et al., 2008) สายอื่น ๆ ของหลักฐานที่ชี้ให้เห็นว่าการเบี่ยงเบนจากวิถีการพัฒนาปกติในรูปแบบงานที่เกี่ยวข้องกับการกระตุ้นสมองหรือการปรากฏตัวของneurophysiological นี้ (Gee et al, 2012). การปรับเปลี่ยนที่รู้จักกันที่จะเชื่อมโยงกับโรคจิตเภท (Shaikh et al, 2012;. Ziermans et al, . 2012) คาดการณ์การแปลง การศึกษาเหล่านี้เป็นตัวแทนของตัวอย่างที่สำคัญของความคืบหน้าการทำในการระบุบุคคลที่มีความเสี่ยงและในการทำนายการแปลงทางคลินิกโรคจิตเภทแต่การศึกษาต่อไปมีความจำเป็นก่อนที่จะ pre- จองแทรกแซงสามารถนำมาใช้อย่างน่าเชื่อถือโดยเฉพาะอย่างยิ่งถ้าการแทรกแซงผู้ดำเนินการที่มีศักยภาพสำหรับผลทางการแพทย์ที่ไม่พึงประสงค์หรือปาน. อนาคตของการแทรกแซงมาตรการสำหรับโรคจิตเภทการใช้งานที่ประสบความสำเร็จของการแทรกแซงมาตรการสำหรับโรคจิตเภทต้องไม่เพียงแต่ความสามารถในการ indentify บุคคลที่มีความเสี่ยง แต่ยังความรู้เกี่ยวกับเวลาและวิธีการที่จะเข้าไปแทรกแซง However, about two-thirds of treatment-seeking individuals who have
two or more of certain characteristics (e.g. genetic risk with recent
deterioration in function, high levels of unusual thought content or
paranoia, social impairment or history of substance use) will convert
(Cannon et al., 2008). Other lines of evidence suggest that deviations
from normal developmental trajectories in task-related patterns of
brain activation (Gee et al., 2012) or the presence of neurophysiological
alterations known to be associated with schizophrenia (Shaikh
et al., 2012; Ziermans et al., 2012) predict conversion. These studies
represent important examples of the progress being made in identifying
at-risk individuals, and in predicting conversion to clinical
schizophrenia, but further studies are needed before pre-emptive
interventions can be reliably applied, especially if those interventions
carry potential for adverse medical effects or stigma.
The future of preemptive interventions for schizophrenia
The successful use of preemptive interventions for schizophrenia
requires not only the ability to indentify at-risk individuals, but also
knowledge of when and how to intervene. Consider, for example, the
potential contribution of a deficient number of dendritic spines on
DLPFC layer 3 pyramidal neurons to the deficits in working memory
that are present before the onset of psychosis. If these spine deficits
reflect a failure in the normal exuberant spine proliferation during the
third trimester of gestation or early childhood, then preemptive
interventions might need to be delivered quite early in life and targeted
to molecular pathways that regulate spine formation. Alternatively, if
spine deficits reflect excessive spine pruning during late childhood–
adolescence (Feinberg, 1982; Hoffman & Dobscha, 1989), then
preemptive interventions could be delivered later and directed at
molecular pathways that regulate spine maintenance. The idea that a
deficit in the excitatory connectivity of DLPFC layer 3 pyramidal
neurons, which is critical for normal working memory function
(Goldman-Rakic, 1995), arises during late childhood–adolescence is
consistent with evidence that individuals who are later diagnosed with
schizophrenia have normal working memory function at age 7 years,
but then fail to show the typical age-related improvement in working
memory performance (Reichenberg et al., 2010). In addition, teenagers
at high risk for schizophrenia, especially those who later became
psychotic, had poorer performance on neurocognitive measures than
comparison subjects, although this dysfunction was milder than in
individuals in their first psychotic episode (Seidman et al., 2010).
Finally, many studies indicate that high-risk subjects who convert to
schizophrenia have greater reductions in PFC gray matter volume
during adolescence than do non-converters (Pantelis et al., 2003;
Borgwardt et al., 2007; Sun et al., 2009; McIntosh et al., 2011;
Mechelli et al., 2011), an expected finding if spines are being
excessively pruned. Furthermore, the expression of gene products that
have been implicated in spine maintenance are altered in schizophrenia,
providing both a potential molecular basis for excessive spine
pruning and novel drug targets (Hill et al., 2006; Ide & Lewis, 2010).
The design of preemptive interventions directed against spine deficits
might also be informed by knowledge of the types of spines that are
affected. Spines have distinct morphologies that reflect different types of
synaptic plasticity; small, thin (learning) spines are considered to be
transient and critical for rapid plasticity, whereas large, mushroomshaped
(memory) spines are thought to be stable and essential for longterm
plasticity (Kasai et al., 2003). Thin spines have been proposed to be
key elements in ‘dynamic network connectivity’, an ongoing and rapid
strengthening or elimination of excitatory connections in the DLPFC
that provides the mental flexibility characteristic of working memory
(Arnsten et al., 2010). Consistent with this hypothesis, thin spine
density in monkey DLPFC is positively correlated with working
memory ability (Dumitriu et al., 2010). If a lower density of thin spines
in the DLPFC contributes to impaired working memory in individuals
with schizophrenia, then it may be possible to reverse this deficit through
pharmacological means. For example, estrogen treatment increases thin
spine density in monkey DLPFC (Tang et al., 2004; Hao et al., 2007),
and estrogen receptor modulators have been reported to improve
symptoms in postmenopausal women with schizophrenia (Kulkarni
et al., 2010; Usall et al., 2011).
The decrease in presynaptic GAD67 (Curley et al., 2011) and
postsynaptic GABAA a1 subunit-containing receptors (Glausier &
Lewis, 2011) at PV basket neuron inputs to layer 3 pyramidal neurons
in schizophrenia suggest that PV basket cell inhibition is lower in
schizophrenia. Such a reduction in inhibition has been hypothesized to
represent a compensatory response to an upstream deficit in layer 3
pyramidal cell excitation (due to their dendritic spine deficit) that
would help re-balance DLPFC excitation and inhibition (Lewis et al.,
2012). The presynaptic downregulation of GAT1 (Woo et al., 1998)
and the postsynaptic upregulation of GABAA a2 subunit-containing
receptors (Volk et al., 2002) at PV chandelier cell–pyramidal cell
inputs are also thought to be compensatory to the spine deficit,
because in ‘quiet’ circuits GABA inputs from chandelier cells can be
excitatory (Woodruff et al., 2011). Consistent with this hypothesis, in
proof-of-concept studies a novel compound that enhances GABA
neurotransmission at GABAA receptors containing a2 subunits was
associated with improved working memory performance in subjects
with schizophrenia (Lewis et al., 2008) and in an animal model of the
cognitive deficits of schizophrenia (Castner et al., 2010), although a
larger clinical trial in chronically ill subjects with schizophrenia did
not show evidence of benefit (Buchanan et al., 2011). The possibility
that this or a related therapeutic strategy would be of benefit at an early
stage of the illness, especially prior to the onset of psychosis, remains
to be determined (Lewis, 2011).
The alterations in cortical circuits that underlie the cognitive
abnormalities in schizophrenia might also be targeted through
behavioral interventions. For example, recent studies using different
behavioral approaches have reported functional improvements in
individuals with schizophrenia. Subjects with chronic schizophrenia
who participated in 80 hours of computerized training of cognitive
processes, compared with those engaged in a computer games control
condition, exhibited improvement in reality monitoring and improved
social functioning 6 months later (Subramaniam et al., 2012). Relative
to patients with chronic schizophrenia who received standard treatment
alone, those who also received up to 18 months of cognitive
therapy focused on correcting dysfunctional beliefs and adapted for
neurocognitive impairments exhibited improvements in global functioning
and reductions in both avolition and positive symptoms (Grant
et al., 2012). A 2-year trial of cognitive enhancement therapy, which
combines computer-assisted neurocognitive training and group-based
social cognition exercises, was associated with both improvement in
social cognition and greater preservation of gray matter volume in
patients with schizophrenia treated within the first 5 years of onset of
psychosis (Eack et al., 2010). The effectiveness of these interventions
might actually be greater if used in individuals at risk, but before the
onset of psychosis, as the intervention would be delivered at a stage of
life when the targeted neural circuits normally have greater plasticity,
and before the function of these circuits has borne the brunt of illness
chronicity. In addition, relative to pharmacological approaches,
behavioral interventions offer potential advantages in terms of a
lower risk of adverse side-effects and less stigma.
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