Diseases under autism
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I now have sufficient information from the textbooks. Here is a comprehensive overview:
Autism Spectrum Disorder (ASD) — Associated Conditions & Classification
What is ASD?
Autism Spectrum Disorder (ASD) is a phenotypically heterogeneous group of neurodevelopmental syndromes characterized by:
- Deficits in social communication and interaction
- Restricted and repetitive behaviors
It is typically evident during the second year of life, though milder cases may go unidentified until middle childhood.
Disorders Under the Autism Spectrum (Pre-DSM-5 Classification)
Before DSM-5, five overlapping disorders were recognized under the umbrella of Pervasive Developmental Disorders (PDDs). DSM-5 collapsed them all into the single diagnosis of Autism Spectrum Disorder, but they remain clinically important:
| Disorder | Key Features |
|---|---|
| Autistic Disorder (Classic Autism) | Core deficits in social communication + repetitive behaviors; often with language delay and intellectual disability |
| Asperger Disorder | Social impairment + repetitive behaviors, but without significant language delay or intellectual disability |
| Rett Syndrome | Predominantly in females; normal development for ≥6 months → stereotyped hand movements, loss of purposeful hand use, declining social engagement, poor coordination, decreasing language. Now linked to MECP2 gene mutation |
| Childhood Disintegrative Disorder | Normal development for ~2 years → loss of skills in language, social responsiveness, play, motor skills, or bladder/bowel control |
| Pervasive Developmental Disorder – Not Otherwise Specified (PDD-NOS) | Subthreshold or atypical presentations that don't fully meet criteria for the above |
ICD-10 still recognizes these as separate entities. DSM-5 uses the unified ASD label.
Conditions Commonly Co-occurring with ASD
ASD frequently occurs alongside other neurodevelopmental and psychiatric conditions:
| Co-occurring Condition | Notes |
|---|---|
| Intellectual Disability | ~1/3 of children with ASD meet criteria for intellectual disability |
| ADHD (Hyperactivity, Impulsivity, Inattention) | Very common; methylphenidate and atomoxetine studied for ASD+ADHD |
| Epilepsy / Seizure Disorders | Elevated prevalence in ASD |
| Anxiety Disorders | Frequently co-morbid |
| Mood Disorders / Irritability | Treated with risperidone (FDA-approved) or aripiprazole (FDA-approved) |
| Self-injurious Behavior | Common in severe ASD |
| Obsessive-Compulsive-like behaviors | Repetitive and stereotyped behaviors can overlap with OCD |
| Language/Communication Disorders | Aberrant language development is an associated (not core) feature in DSM-5 |
| Gastrointestinal disorders | Higher prevalence reported in ASD populations |
Genetic Associations
ASD has a significant heritable contribution (family and twin studies). Key genetic links include:
- Fragile X syndrome — most common single-gene cause of ASD
- Tuberous sclerosis
- MECP2 mutations — associated with Rett syndrome
- Chromosomal copy number variants (CNVs) — deletions/duplications at multiple loci
- Up to 15% of cases may have an identifiable genetic etiology
DSM-5 Severity Levels
DSM-5 specifies severity based on the level of support required:
| Level | Social Communication | Restricted/Repetitive Behaviors |
|---|---|---|
| Level 1 (Requiring support) | Noticeable impairments without support | Inflexibility causes significant interference |
| Level 2 (Requiring substantial support) | Marked deficits, limited social interaction | Frequent behaviors noticeable to casual observers |
| Level 3 (Requiring very substantial support) | Severe deficits, very limited social initiation | Extreme difficulty with flexibility, distress when changed |
Pharmacological Management Summary
| Target Symptom | Drug | Notes |
|---|---|---|
| Irritability / Aggression | Risperidone (FDA-approved), Aripiprazole (FDA-approved) | First-line for severe irritability |
| Hyperactivity / Inattention | Methylphenidate, Atomoxetine, Guanfacine, Clonidine | Less effective than in pure ADHD |
| Repetitive Behaviors | Fluoxetine (modest evidence), mood stabilizers | Mixed results in studies |
| Olanzapine | Irritability | Significant weight gain limits use |
Sources: Kaplan and Sadock's Synopsis of Psychiatry; Kaplan & Sadock's Comprehensive Textbook of Psychiatry
Pervasive
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Here is a detailed breakdown of all Pervasive Developmental Disorders (PDDs) — the original classification system that preceded DSM-5's unified ASD diagnosis:
Pervasive Developmental Disorders (PDDs)
Pervasive Developmental Disorders was the umbrella term used in DSM-IV and remains partially in ICD-10. It included five distinct disorders, all sharing impairments in socialization, communication, and behavior — but differing in severity, onset, and specific features.
DSM-5 collapsed all five into a single diagnosis: Autism Spectrum Disorder (ASD).
1. Autistic Disorder (Classic Autism)
Core triad of impairments:
- Deficits in social communication and interaction
- Restricted, repetitive behaviors and interests
- Language delay (often severe)
Key features:
- Typically identified in the second year of life (severe cases in the first year)
- Poor or absent eye contact; atypical attachment behavior
- Children may not differentiate parents from strangers
- Intense interest in narrow, idiosyncratic topics
- ~1/3 have co-occurring intellectual disability
- In up to 25% of cases, some language develops and is subsequently lost
- Average age of diagnosis: ~3.1 years
2. Asperger Disorder (Asperger Syndrome)
Core features:
- Impairment in social relatedness
- Repetitive and stereotyped behaviors
- No significant language delay
- No intellectual disability — cognitive and adaptive skills are age-appropriate
Key distinction from autistic disorder:
- Social communication is impaired, but language and cognitive function are preserved
- Often goes undiagnosed until middle childhood or later
- Average age of diagnosis: ~7.2 years (much later than classic autism)
- Subtle deficits in pragmatic language (e.g., back-and-forth conversation, reading social cues)
3. Rett Syndrome
Pattern:
- Occurs almost exclusively in females
- Associated with MECP2 gene mutation (X-linked)
Phases:
| Phase | Features |
|---|---|
| Early (0–6 months) | Normal development |
| Regression | Stereotyped hand-wringing movements; loss of purposeful hand use |
| Continued regression | Diminishing social engagement, declining language, poor coordination |
| Late | Severe intellectual and motor disability; seizures common |
Key point: Rett syndrome was removed from DSM-5 ASD due to its known genetic cause, but remains in ICD-10. High glutamate levels have been found in these patients.
4. Childhood Disintegrative Disorder (Heller's Syndrome)
Pattern:
- Normal development for at least 2 years
- Followed by significant regression in at least 2 of these areas:
- Language (expressive or receptive)
- Social responsiveness
- Play
- Motor skills
- Bladder or bowel control
Key distinction: The extended period of normal development (≥2 years) before regression sets it apart from classic autism.
Prognosis: Generally poor; most retain severe impairment. Rarer than autistic disorder.
5. Pervasive Developmental Disorder — Not Otherwise Specified (PDD-NOS)
Also called atypical autism in ICD-10.
Features:
- Subthreshold presentation — does not fully meet criteria for any of the above disorders
- Impairments in social interaction + either communication deficits OR repetitive behaviors, but not all criteria met
- Average age of diagnosis: ~3.9 years
- Functions as a "catch-all" for clinically significant autistic features that don't fit elsewhere
Summary Comparison Table
| Disorder | Language Delay | Intellectual Disability | Onset | Sex Bias | Genetic Link |
|---|---|---|---|---|---|
| Autistic Disorder | Yes (often severe) | ~1/3 of cases | Year 1–2 | M > F (4:1) | Polygenic |
| Asperger Disorder | No | No | Later childhood | M > F | Polygenic |
| Rett Syndrome | Yes (progressive) | Yes (severe) | After 6 months | Female only | MECP2 mutation |
| Childhood Disintegrative Disorder | Yes (regression) | Yes | After age 2 | M slightly > F | Unknown |
| PDD-NOS | Variable | Variable | Variable | M > F | Variable |
DSM-5 / ICD-10 Status
| Classification System | Approach |
|---|---|
| DSM-5 | All five collapsed into Autism Spectrum Disorder (single continuum diagnosis with severity levels 1–3) |
| ICD-10 | Retains separate categories (Childhood Autism, Atypical Autism, Asperger Syndrome, Rett Syndrome, etc.) |
Sources: Kaplan and Sadock's Synopsis of Psychiatry; Kaplan & Sadock's Comprehensive Textbook of Psychiatry
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