Screening, Diagnosis, and Investigation of Global Developmental Delay and Intellectual Developmental Disorder

Global developmental delay (GDD) and intellectual developmental disorder (IDD) are significant neurodevelopmental conditions in the pediatric population. These conditions result from complex interactions between genetic and environmental factors.

To standardize the screening, diagnosis, and etiological investigation of GDD/IDD in a Neurodevelopment outpatient setting and to determine the main etiologies and diagnostic yield of first-line tests.

A standardized protocol was established for the screening, diagnosis, and etiological investigation of GDD and IDD. The study population comprised children undergoing clinical evaluation for GDD or IDD, assessed prospectively between July 2018 and June 2021, with follow-up data collected until 2024. Developmental and cognitive assessment tools included the Griffiths Mental Development Scales - Third Edition (GMDS-III), the Wechsler Preschool and Primary Scale of Intelligence - Revised (WPPSI-R), and the Wechsler Intelligence Scale for Children - Third Edition (WISC-III). GDD was defined in children aged ≤5 years with a developmental quotient (DQ) or equivalent intelligence quotient (IQeq) below 70. IDD was defined in individuals aged >5 years with IQeq <70, or in cases of severe/profound IDD where standardized testing could not be administered. Statistical analysis was conducted using IBM SPSS® Statistics, version 29 (IBM Corp., Armonk, NY).

A total of 123 children were included, comprising 34 with GDD and 89 with IDD, of whom 30 (34%) had a previous GDD diagnosis. The cohort was predominantly male (65%). In the GDD group, the Griffiths Scale was used in 19 children (mean DQ = 56) and the WPPSI-R in 15 (mean DQ = 51). In the IDD group, the Griffiths Scale was applied in eight (mean DQ = 66.5), the WPPSI-R in 5 (mean DQ = 66.5), and the WISC-III in 76 (mean DQ = 64). First-line etiological investigations included array-CGH in 52 (42%) children, identifying 8 pathogenic variants; FMR1 testing in 39 (32%), identifying two positive cases; and karyotype analysis in 13 (11%), identifying three abnormalities. Cranial MRI was performed in 22 (18%), with abnormal findings in 6 (27%), and EEG in 32 (26%), showing abnormalities in 18 (56%). Autism spectrum disorder was the most frequent associated diagnosis.

A structured protocol enhanced diagnostic consistency and efficiency in children with GDD and IDD. Genetic testing, particularly array-CGH, FMR1 analysis, and karyotype, proved most informative, yielding an overall etiological diagnosis rate of 11%. These findings highlight the importance of evidence-based protocols for comprehensive evaluation and genetic counseling.