AIM: Mutations in the SLC16A2 gene have been implicated in Allan-Herndon-Dudley 
syndrome (AHDS), an X-linked learning disability* syndrome associated with 
thyroid function test (TFT) abnormalities. Delayed myelination is a non-specific 
finding in individuals with learning disability whose genetic basis is often 
uncertain. The aim of this study was to describe neuroimaging findings and 
neurological features in males with SLC16A2 gene mutations.
METHOD: We reviewed brain magnetic resonance imaging (MRI) findings and 
neurological features in a cohort of five males aged between 1 year 6 months and 
6 years (median 4y) from four families harbouring SLC16A2 gene mutations.
RESULTS: The participants presented aged between 4 and 9 months with initial 
hypotonia and subsequent spastic paraparesis with dystonic posturing and 
superimposed paroxysmal dyskinesias. Dystonic cerebral palsy was the most common 
initial clinical diagnosis, and AHDS was suspected only retrospectively, 
considering the characteristically abnormal thyroid function tests, with high 
serum tri-iodothyronine (T(3)), as the most consistent finding. Brain MRI showed 
absent or markedly delayed myelination in all five participants, prompting the 
suspicion of Pelizaeus-Merzbacher disease in one patient.
INTERPRETATION: Our findings indicate a consistent association between defective 
neuronal T(3) uptake and delayed myelination. SLC16A2 involvement should be 
considered in males with learning disability, an associated motor or movement 
disorder, and evidence of delayed myelination on brain MRI. Although dysmorphic 
features suggestive of AHDS are not always present, T(3) measurement is a 
reliable screening test.