Clinical Picture and Etiology of Neurodevelopmental Disorders: Attention-Deficit/Hyperactivity Disorder (ADHD), Autism Spectrum Disorders, Intellectua

Neurodevelopmental Disorders (DSM-5)

These disorders begin early in development, often before school age, and are characterized by developmental deficits that cause impairments of personal, social, academic, or occupational functioning.

1. Attention-Deficit/Hyperactivity Disorder (ADHD)

Clinical Picture:

• Key Features:

  • Persistent pattern of inattention and/or hyperactivity-impulsivity.

  • Interferes with functioning or development.

  • Symptoms present before age 12 years.

  • Symptoms observed in two or more settings (e.g., home, school, work).

• Inattention symptoms (examples):

  • Fails to give close attention to details; careless mistakes.

  • Difficulty sustaining attention in tasks or play.

  • Seems not to listen when spoken to directly.

  • Difficulty organizing tasks and activities.

  • Avoids/dislikes tasks requiring sustained mental effort.

  • Often loses things necessary for tasks (e.g., school materials, keys).

  • Easily distracted by extraneous stimuli.

  • Forgetful in daily activities.

• Hyperactivity and impulsivity symptoms (examples):

  • Fidgets, taps hands or feet, squirms in seat.

  • Leaves seat when remaining seated is expected.

  • Runs about or climbs in inappropriate situations (in adolescents/adults: restlessness).

  • Unable to play or engage quietly.

  • "On the go," acting as if "driven by a motor."

  • Talks excessively.

  • Blurts out answers before questions are completed.

  • Difficulty waiting turn.

  • Interrupts or intrudes on others.

• Specifiers (presentation types):

  • Predominantly Inattentive Presentation

  • Predominantly Hyperactive-Impulsive Presentation

  • Combined Presentation

Etiology:

• Genetic factors:

  • High heritability (up to 76%).

  • First-degree relatives have higher rates.

• Neurobiological factors:

  • Dysfunction in frontal-striatal circuits (prefrontal cortex and basal ganglia).

  • Deficits in dopamine and norepinephrine systems.

• Environmental factors:

  • Low birth weight, prenatal exposure to tobacco or alcohol.

  • Lead exposure.

• Psychosocial factors:

  • Family adversity and parental psychopathology may exacerbate symptoms but do not cause ADHD.

2. Autism Spectrum Disorder (ASD)

Clinical Picture:

• Key Features:

  • Persistent deficits in social communication and social interaction across multiple contexts.

  • Restricted, repetitive patterns of behavior, interests, or activities.

  • Symptoms must be present in the early developmental period.

  • Symptoms cause clinically significant impairment.

• Social communication deficits (examples):

  • Deficits in social-emotional reciprocity (e.g., abnormal social approach, reduced sharing of interests/emotions).

  • Deficits in nonverbal communicative behaviors (e.g., abnormal eye contact, lack of facial expressions).

  • Deficits in developing, maintaining, and understanding relationships.

• Restricted and repetitive behaviors (examples):

  • Stereotyped or repetitive motor movements, use of objects, or speech (e.g., echolalia).

  • Insistence on sameness, inflexible adherence to routines.

  • Highly restricted, fixated interests (e.g., strong attachment to unusual objects).

  • Hyper- or hyporeactivity to sensory input (e.g., adverse response to specific sounds/textures).

• Severity Specifiers:

  • Based on level of support required for social communication and restricted behaviors.

• Associated Features:

  • Intellectual disability and/or language impairment.

  • Motor deficits, including odd gait.

  • Self-injurious behavior.

  • Uneven cognitive abilities (e.g., strengths in memory but deficits in abstract thinking).

Etiology:

• Genetic factors:

  • High heritability; concordance rates are higher in monozygotic twins.

  • Multiple genetic pathways; rare mutations and chromosomal abnormalities (e.g., fragile X syndrome) linked.

• Neurobiological factors:

  • Abnormalities in brain structure and function (e.g., accelerated brain growth early in life).

  • Differences in amygdala, hippocampus, and cerebellum.

• Environmental factors:

  • Advanced parental age, prenatal exposure to certain medications (e.g., valproate).

  • Very low birth weight and prenatal infections might increase risk.

• Psychosocial factors:

  • No evidence that parenting style causes ASD (debunks "refrigerator mother" theory).

3. Intellectual Disability (Intellectual Developmental Disorder)

Clinical Picture:

• Key Features:

  • Deficits in intellectual functions confirmed by clinical assessment and standardized testing (IQ approximately 70 or below).

  • Deficits in adaptive functioning that result in failure to meet developmental and sociocultural standards for personal independence and social responsibility.

  • Onset during the developmental period (childhood).

• Areas of Deficits:

  • Conceptual domain: Academic learning, abstract thinking, executive function.

  • Social domain: Awareness of others’ experiences, empathy, interpersonal communication skills, social judgment.

  • Practical domain: Personal care, job responsibilities, money management, recreation.

• Severity Specifiers (based on adaptive functioning, not IQ alone):

  • Mild

  • Moderate

  • Severe

  • Profound

• Associated Features:

  • Motor deficits, difficulties in emotional regulation.

  • Risk for psychiatric comorbidities (e.g., mood disorders, ADHD).

Etiology:

• Genetic factors:

  • Chromosomal disorders (e.g., Down syndrome, fragile X syndrome).

  • Single-gene disorders.

• Prenatal factors:

  • Maternal infections (e.g., rubella, cytomegalovirus).

  • Exposure to toxins (e.g., alcohol — fetal alcohol syndrome).

  • Malnutrition during pregnancy.

• Perinatal factors:

  • Birth complications (e.g., asphyxia, prematurity).

• Postnatal factors:

  • Traumatic brain injury.

  • Severe neglect or abuse.

  • Severe environmental deprivation.

• Unknown causes:

  • In many cases, the exact cause remains unidentified.

Summary Table