Enigma of autism regression mechanistic pathways, clinical phenotypes, and early intervention implications

Table 7 “Never-miss” clinical red flags in children with developmental regression

If you see	Think	Order
Loss of motor skills + hand wringing	Rett syndrome	MECP2 genetic testing
Sudden loss of word understanding	LKS	Overnight sleep EEG
Regression + “sweet” smelling breath/sweat	Metabolic disorder	Urine organic acids/plasma amino acids
Regression + seizures + large head	15q duplication	Chromosomal microarray

The table highlights specific presentations that should prompt consideration of alternative or comorbid diagnoses beyond idiopathic regressive autism and outlines the recommended first-line diagnostic test for each scenario. Early recognition is essential, as several listed conditions have time-sensitive, condition-specific treatments. LKS: Landau-Kleffner syndrome; EEG: Electroencephalogram.