Two genes have been identified as incurring vulnerability for depressive disorder. The first one, the MAOA gene, is responsible for the functioning of monoamine oxidase, and the second is the serotonin transporter gene (5-HTT). The serotonin transporter gene, which is involved in the process of making serotonin available, is present in homozygous long alleles, a heterozygous one long and one short allele pair, and homozygous short alleles. A large longitudinal study in New Zealand found a relationship of early environmental stress and subsequent depression in children with one or two short alleles, but not in those children in the sample with
two long alleles. Because the short alleles are less efficient in transcription, this finding suggests that the availability of the transporter gene may provide a marker for vulnerability to depression. Thus, a stress-diathesis model for the emergence of depression may best fit with these data.

The finding that identical twins do not have 100 percent concordance suggests a role for nongenetic factors in the emergence of major depressive disorder. Despite a lack of definitive evidence, given the stress-diathesis hypotheses of depression, genetic vulnerability in combination with a variety of social factors, including level of family conflict, abuse or neglect, conflict, family socioeconomic status, and parental separation or divorce, may play a significant role in the emergence of depressive disorders in children. Evidence indicates that boys whose fathers died before they were 13 years of age are at greater risk than controls to develop depression.

The psychosocial impairment that characterizes depressed children lingers far after recovery from the index episode of depression. These deficits can be compounded by the relatively long duration of at least 1 year for a dysthymic episode and an average of 9 months to 1 year for a depressive episode in a child or adolescent. For an adolescent, a major depressive episode significantly interferes with social and academic skills, which are poorly accomplished or unaccomplished during the episode. Among preschoolers with depressive clinical presentations, the role of environmental influences is likely to have a significant impact on the course and recovery of the young child.

Major depressive disorder in children is diagnosed most easily when it is acute and occurs in a child without previous psychiatric symptoms. Often, however, the onset is insidious, and the disorder occurs in a child who has had several years of difficulties with hyperactivity, separation anxiety disorder, or intermittent depressive symptoms.

According to the DSM-IV-TR diagnostic criteria for major depressive episode, at least five symptoms must be present for a period of 2 weeks, and there must be a change from previous functioning. Among the necessary symptoms is either a depressed or irritable mood or a loss of interest or pleasure. Other symptoms from which the other four diagnostic criteria are drawn include a child’s failure to make expected weight gains, daily insomnia or hypersomnia, psychomotor agitation or retardation, daily fatigue or loss of energy, feelings of worthlessness or inappropriate guilt, diminished ability to think or concentrate, and recurrent thoughts of death. These symptoms must produce social or academic impairment. To meet the diagnostic criteria for major depressive disorder, the symptoms cannot be the direct effects of a substance (e.g., alcohol) or a general medical condition. A diagnosis of major depressive disorder is not made within 2 months of the loss of a loved one, except when marked functional impairment, morbid preoccupation with worthlessness, suicidal ideation, psychotic symptoms, or psychomotor retardation is present.

A major depressive episode in a prepubertal child is likely to be manifest by somatic complaints, psychomotor agitation, and mood-congruent hallucinations. Anhedonia is also frequent, but anhedonia, as well as hopelessness, psychomotor retardation, and delusions, are more common in adolescent and adult major depressive episodes than in those of young children. Adults have more problems with sleep and appetite than depressed children and adolescents. In adolescence, negativistic or frankly antisocial behavior and the use of alcohol or illicit substances can occur and may justify the additional diagnoses of oppositional defiant disorder, conduct disorder, and substance abuse or dependence. Feelings of restlessness, grouchiness, aggression, sulkiness,
reluctance to cooperate in family ventures, withdrawal from social activities, and a desire to leave home are all common in adolescent depression. School difficulties are likely. Adolescents may be inattentive to personal appearance and show increased emotionality, with particular sensitivity to rejection in love relationships.

Children can be reliable reporters about their own behavior, emotions, relationships, and difficulties in psychosocial functions. They may, however, refer to their feelings by many names. Clinicians, therefore, must ask children about feeling sad, empty, low, down, blue, or very unhappy and about feeling like crying or about having a bad feeling that is present most of the time. Depressed children usually identify one or more of these terms as their persistent feeling. Clinicians should assess the duration and periodicity of the depressive mood to differentiate relatively universal, short-lived, and sometimes frequent periods of sadness, usually after a frustrating event, from a true, persistent depressive mood. The younger the child, the more imprecise his or her time estimates are likely to be.

Mood disorders tend to be chronic if they begin early. Childhood onset may be the most severe form of mood disorder and tends to appear in families with a high incidence of mood disorders and alcohol abuse. The children are likely to have such secondary complications as conduct disorder, alcohol and other substance abuse, and antisocial behavior. Functional impairment associated with a depressive disorder in childhood extends to practically all areas of a child’s psychosocial world; school performance and behavior, peer relationships, and family relationships all suffer. Only highly intelligent and academically oriented children with no more than a moderate depression can compensate for their difficulties in learning by substantially increasing their time and effort. Otherwise, school performance is invariably affected by a combination of difficulty concentrating, slowed thinking, lack of interest and motivation, fatigue, sleepiness, depressive ruminations, and preoccupations. Depression in a child may be misdiagnosed as a learning disorder. Learning problems secondary to depression, even when long-standing, are corrected rapidly after a child’s recovery from the depressive episode.

Children and adolescents with major depressive disorder may have hallucinations and delusions. Usually, these psychotic symptoms are thematically consistent with the depressed mood, occur with the depressive episode (usually at its worst), and do not include certain types of hallucinations (such as conversing voices and a commenting voice, which are specific to schizophrenia). Depressive hallucinations usually consist of a single voice speaking to the person from outside of his or her head, with derogatory or suicidal content. Depressive delusions center on themes of guilt, physical disease, death, nihilism, deserved punishment, personal inadequacy, and (sometimes) persecution. These delusions are rare in prepuberty, probably because of cognitive immaturity, but are present in about one half of psychotically depressed adolescents.

Adolescent onset of a mood disorder can be difficult to diagnose when first seen if the adolescent has attempted self-medication with alcohol or other illicit substances. In a recent study, 17 percent of young persons with a mood disorder first received medical attention because of substance abuse. Only after detoxification could the psychiatric symptoms be assessed properly and the mood disorder diagnosed correctly.

Dysthymic disorder in children and adolescents consists in a depressed or irritable mood for most of the day, for more days than not, over a period of at least 1 year. DSM-IV-TR notes that in children and adolescents, irritable mood can replace the depressed mood criterion for adults and that the duration criterion is not 2 years but 1 year. According to the DSM-IV-TR diagnostic criteria, at least three of the following symptoms must accompany the depressed or irritable mood: poor self-esteem, pessimism or hopelessness, loss of interest, social withdrawal, chronic fatigue, feelings of guilt or brooding about the past, irritability or excessive anger, decreased activity or productivity, and poor concentration or memory. During the year of the disturbance, these symptoms do not resolve for more than 2 months at a time. In addition, the diagnostic criteria for dysthymic disorder specify that during the first year, no major depressive episode emerges. To meet the DSM-IV-TR diagnostic criteria for dysthymic disorder, a child must not have a history of a manic or hypomanic episode. Dysthymic disorder is also not diagnosed if the symptoms occur exclusively during a chronic psychotic disorder or if they are the direct effects of a substance or a general medical condition. DSM-IV-TR provides for specification of early onset (before 21 years of age) or late onset (after 21 years of age).

A child or adolescent with dysthymic disorder may have had a major depressive episode before developing a dysthymic disorder, but it is much more common for a child with dysthymic disorder for more than 1 year to have major depressive episode. In this case, both depressive diagnoses are given (double depression). Dysthymic disorder in children is known to have an average age of onset that is several years earlier than the age of onset of major depressive disorder. Controversy exists among clinicians and researchers about whether dysthymic disorder is best categorized as a chronic, insidious version of major depressive disorder or represents a separate disorder. Occasionally, young persons fulfill the criteria for dysthymic disorder, except that their episodes last only 2 weeks to several months, with symptom-free intervals lasting for 2 to 3 months. These minor mood presentations in children are likely to indicate severe mood disorder episodes in the future. Knowledge suggests that the longer, the more recurrent, the more frequent, and perhaps the less related to social stress these episodes are, the greater is the likelihood of a severe mood disorder in the future. When minor depressive episodes follow a significant stressful life event by less than 3 months, it is often part of an adjustment disorder.