Using whole exome sequencing and subsequent Sanger sequencing, we identified truncating and missense mutations in the THRA gene in five of six individuals and describe a distinct and consistent phenotype of mild hypothyroidism (growth retardation, relatively high birth length and weight, mild-to-moderate mental retardation, mild skeletal dysplasia and constipation), specific facial features (round, somewhat coarse and flat face) and macrocephaly.