What is Pervasive Developmental Disorder (PDD)?

Pervasive Developmental Disorder (PDD)

Pervasive Developmental Disorder (PDD) is a group of neurodevelopmental conditions characterized by impairments in social interaction, communication, and restricted, repetitive patterns of behavior that has now been reclassified under Autism Spectrum Disorder (ASD) in the DSM-5 due to lack of evidence supporting reliable diagnostic differences among PDD subtypes. 1

Definition and Classification

PDD previously encompassed several conditions in the DSM-IV-TR:

• Autistic Disorder: Characterized by marked impairment in social interaction, communication, and restricted/repetitive behaviors with onset before age 3
• Asperger's Disorder: Distinguished by preserved language acquisition and formal speech but with social difficulties and restricted interests
• PDD-Not Otherwise Specified (PDD-NOS): Subthreshold cases with social interaction problems and some communication difficulties or restricted behaviors
• Childhood Disintegrative Disorder (CDD): Normal development for at least 2 years followed by significant regression in multiple skill areas
• Rett's Disorder: Primarily affecting females, caused by MeCP2 gene mutations with characteristic hand-wringing stereotypies 1

Diagnostic Evolution

In 2013, the DSM-5 consolidated these conditions under a single diagnosis of Autism Spectrum Disorder (ASD) because:

• There was insufficient evidence to support reliable diagnostic differences among PDD subtypes 1
• Diagnostic domains were reduced from three to two: (1) social communication/interaction deficits and (2) restricted, repetitive patterns of behaviors and interests
• The strict requirement for onset before age 3 was changed to "early developmental period"
• Sensory abnormalities were incorporated into the diagnostic criteria
• Severity scales were added for each core domain 1

Clinical Features

PDD/ASD is characterized by:

1. Social communication impairments:

   • Difficulty with social-emotional reciprocity
   • Deficits in nonverbal communication
   • Challenges developing and maintaining relationships

2. Restricted, repetitive patterns of behavior:

   • Stereotyped or repetitive movements
   • Insistence on sameness and routines
   • Highly restricted, fixated interests
   • Hyper- or hypo-reactivity to sensory input 1, 2

Epidemiology

• Current prevalence estimates of ASD are approximately 1 in 110 children (9 per 1,000) 1
• Earlier studies of autism alone showed prevalence of 10-16 per 10,000 1
• More recent studies suggest higher rates, with significant increases in diagnosed cases over the past two decades 1
• Males are affected 3-4 times more frequently than females 1

Etiology

The etiology of PDD/ASD is multifactorial with strong genetic components:

• Genetic factors (primary role):

  • Heritability estimated at approximately 90% 2
  • Sibling recurrence risk of 4-19%, much higher than general population 1, 2
  • Specific recurrence risks: 7% if first affected child is female, 4% if male 1
  • If multiple children are affected, recurrence risk increases to 25-35% 1
  • Twin studies show 70% concordance in monozygotic twins (90% using broader phenotypic definition) versus 3% in dizygotic twins 1

• Associated genetic conditions:

  • Tuberous sclerosis complex
  • Fragile X syndrome
  • Rett syndrome
  • Chromosomal abnormalities (15q11-13, 7q22-31, 13q, 17q11, 2q, 16p) 2

• Environmental factors:

  • Advanced parental age
  • Closer spacing of pregnancies
  • Extreme prematurity (<26 weeks gestation)
  • Prenatal exposure to certain environmental chemicals 2

Clinical Presentation and Recognition

• First symptoms typically appear during the first two years of life, but diagnosis is often delayed 3
• Children with autism show first symptoms at mean age of 15 months but are diagnosed at mean age of 76 months 3
• Children with Asperger's syndrome show first symptoms at mean age of 26 months but are diagnosed at mean age of 110 months 3
• PDD-NOS has been found to have a distinct pattern in most cases (97%) - impairments in social reciprocity and communication without significant repetitive and stereotyped behaviors 4

Comorbidities

Individuals with PDD/ASD frequently have comorbid conditions:

• Epilepsy (5-46% of cases) 2
• Motor impairments (delayed milestones, apraxia, hypotonia) 2
• Sleep disturbances (53-78% of individuals) 2
• Anxiety disorders 2
• Other psychiatric disorders including affective disorders, schizophrenia-like psychosis, and Tourette's disorder 5

Differential Diagnosis

PDD/ASD must be distinguished from:

• Schizophrenia: Distinguished by age of onset, presence of hallucinations/delusions, and social relationship patterns 1
• Developmental language disorders: These lack other prerequisite symptoms of PDD such as social relatedness issues 1
• Childhood disintegrative disorder: Distinguished by normal development for at least 2 years before regression 1
• Rett syndrome: Primarily affects females with characteristic hand-wringing stereotypies 1

Importance of Early Diagnosis

Early identification and intervention are critical for improving outcomes in individuals with PDD/ASD 2. The significant delay between first symptoms and diagnosis (often 5+ years) highlights the need for:

• Systematic screening
• Training of primary care providers
• Increased awareness of the heterogeneous presentation of these disorders 3

Genetic Evaluation and Counseling

Genetic evaluation is recommended for all individuals with suspected ASD:

• Chromosomal microarray analysis
• Fragile X testing
• MECP2 sequencing (particularly for females) 2

Genetic counseling is essential for families regarding recurrence risk, which is significantly higher than general population prevalence 1, 2.