Table 1.

Results on prevalence rates, risk factors, and explicative hypotheses for depression in ASD.

Study	Sample: n (mean), years, age range	Diagnosis	Assessment of depression	Results on prevalence rates of depression	Risk factors and explicative hypotheses
Gillberg and Billstedt (2000) [7]	n = 35   (age: DK) Range: children and adolescents with autism	ASD	Review of the literature	33% had an additional psychiatric disorder, with depression being the most common diagnosis	Biological factors: comorbid conditions may be markers for underlying pathophysiology
Whitehouse et al. (2009) [10]	n = 35 AS (age: 14.2) Range: 12–17.6 CG: n = 35 NT (age: 14.4) Range: 13.2–16.10	HFASD	CES-DC (Centre for Epidemiological Studies Depression Scale)	33% self-reported significantly higher levels of depressive symptoms than the NT population	Social support: quality of social relationships
Kanner (1943) [11]	n = 11   (age: 5.4) Range: 2.4–11	ASD	DK	One showed tendency towards depression.	Social support: quality of social relationships
Wing (1981) [12]	n = 34   (age: DK) Range: 5–35	HFASD	DK	The most common psychiatric diagnosis was depression (10 subjects: approximately)	Age; cognitive level, capacity for introspection, awareness of deficits (insight), and alexithymia; life events and effects brought about by character came from the domain of repetitive and restricted behaviours
Ghaziuddin et al. (1998) [13]	n = 35 (age: 15) Range: 8–51	HFASD	K–SADS–E (Kiddie-Schedule for Affective Disorders and Schizophrenia-Epidemiological Version)	65% had an additional psychiatric disorder, with depression being the most common (37%)	Histories of first-degree relatives and environmental context
Kanne et al. (2009) [14]	n = 177 (age: 7.3) Range: 3–18 CG: their siblings (n = 148)	Autism	CBCL (Child Behaviour Checklist) C-TRF (Caregiver/Teacher Report Form)	26% presented depression	Cognitive level; histories of first-degree relatives environmental context
Barnhill and Myles (2001) [15]	n = 33 AS (age: 15) Range: 12–17	HFASD	CDI (Children's Depression Inventory)	54% showed depressive symptoms	Cognitive level, capacity for introspection, awareness of deficits (insight), and alexithymia
Leyfer et al. (2006) [16]	n = 109 (age: 9.2) Range: 5–17	Autism	ACI-PL (Autism Comorbidity Interview-Present and Lifetime Version): this is a modification on the Kiddie Schedule for Affective Disorders and Schizophrenia	13% major depression	Biological factors: comorbidity
Mayes et al. (2011) [17]	n = 627 (age: 6.6) Range: 1–17	ASD (64.4% HFASD)	PBS (Pediatric Behaviour Scale)	The maternal descriptions indicated depression in 72% of the HFASD cases	Gender; age; cognitive level, capacity for introspection, awareness of deficits (insight), and alexithymia; social support: quality of social relationships
Mayes et al. (2011) [18]	n = 233 (age: 8.3) Range: 6–16	HFASD (IQ > 79)	PBS	54% of the mothers reported depression in their children	Age; cognitive level, capacity for introspection, awareness of deficits (insight), and alexithymia
Green et al. (2000) [19]	n = 20 AS (age: 13.75) Range: 11–19 CG: n = 20 (age: 14.47) Range: 11–19	HFASD	ICD-10 (Tenth Revision of the International Classification of Disease)	Higher levels of depression than in the CG. Although only 5% satisfied criteria for major depression, 40% showed chronic unhappiness and 55%, irritability	Biological factors: comorbidity
Hurtig et al. (2009) [20]	n = 43 AS or HFA (age: 13) Range: 11–17 GC: n = 217 (age: 13.5)	HFASD	YSR (Youth Self-Report) CBCL (Child Behaviour Checklist) TRF (Teacher Report Form)	33% self-reported significantly higher levels of depressive symptoms than the NT population	Gender
Kim et al. (2000) [21]	n = 59 (19 AS; 40 HFASD) (age: 12) Range: 9–14 CG: n = 1751 Range: 9–14	HFASD	OCHS-R (Ontario Child Health Study-Revised)	17% significant clinical symptomatology of depression	Biological factors: comorbidity
Meyer et al. (2006) [22]	n = 31 AS age: 10.1 Range: 8–14 CG: n = 33 NT	HFASD	BASC-SRP (Behaviour Assessment System for Children-Self Report of Personality) BASC-PRS (Behaviour Assessment System for Children-Parent Report Scale)	Self-reported symptoms of depression higher than in CG	Cognitive level, capacity for introspection, awareness of deficits (insight), and alexithymia
Brereton et al. (2006) [23]	n = 381/367 ASD (age: 7.4) Range: 3.8–24 GC: n = 581 intellectual disability without ASD	ASD	DBC-P (Developmental Behaviour Checklist)	Parents offered significantly higher scores for behaviour problems, anxiety, depression, and irritability compared with normality, as well as higher degrees of anxiety, behaviour problems, depression, and attention-deficit/hyperactivity disorder than in CG	Gender; age

ASD: Autism Spectrum Disorder; AS: Asperger Syndrome; CG: control group; HFASD: high functioning autism spectrum disorder (IQ > 70); NT: neurotypical.

DK: it indicates that the symptom/sign was not discussed in the paper, not that the authors were unable to assess it.