classic neuroimaging findings described in gm2 gangliosidosis is hyperdense signal in bilateral thalami in non - contrast computed tomography ( ncct ) scan and hypointensity in t2 weighted mri images . hyperdens thalamus in ncct head in a child with neuroregrssion , facial dysmorphism and organomegaly , should lead us to think about gm1 gangliosidosis . a 16-month - old girl presented with history of regression of mile stones for last 6 months . psychomotor development was normal until 12 months of age ; subsequently , she gradually lost ability to sit , neck control , and social smile . she had attained vocabulary of single syllable by 1 year , but subsequently lost it . there was no significant family history . on examination , she had coarse facies , horizontal nystagmus , hepatosplenomegaly , and multiple mongolian spots [ figure 1 ] . on fundus examination , she had bilateral macular cherry red spots [ figure 2 ] . skeletal survey revealed dysostosis multiplex at dorsolumbar junction , as superiorly notched ( inferiorly beaked ) vertebral bodies in the lateral view at the thoracolumbar junction [ figure 3 ] . clinical diagnosis of gm1gangliosidosis was supported with mri brain findings and confirmed with absence of -galactosidase enzyme activity in leukocytes [ figure 4 ] . clinical pictures of a 16-month - oldgirl showing massive hepatosplenomegaly , excessive mongolian spots , and severe failure to thrive photograph of retina in patient with gm1gangliosidosis showing cherry red spot and optic disc edema x - ray of same patient showing dysostosis multiplex at lumbar spine and ncct scan of brain ( axial sections ) at level of thalamus showing bilateral hyperdense thalamus axialt1-weighted image and t2-weighted image at the level of thalamus show diffuse dysmyelination of white matter with bilaterally symmetric thalamic signal change , which appear hyperintense on t1-weighted and hypointense on t2-weighted images gm1gangliosidosis is a rare autosomal recessive lysosomal storage disorder caused by deficiency of lysosomal enzyme -galactosidase , resulting in progressive neural and visceral accumulation of gm1gangliosides , its asialo derivative ga1 , and other minor glycolipids and glycopeptides . three clinical phenotypes can be distinguished and classified by age of onset : infantile , late infantile / juvenile , and adult . the age of onset and rate of progression of the disease depend on the residual activity of enzyme -galactosidase . infantile gm1gangliosidosis , the most common and severe form , is characterized by facial and skeletal abnormalities and neurological deterioration before the age of 6 months . this disorder can be diagnosed by several ways , including lysosomal enzyme assay of low -galactosidase activity in peripheral blood leukocytes or cultured skin fibroblasts , detection of abnormal urinary oligosaccharide excretion , and rectal biopsy . prenatal diagnosis by measurement of enzyme activity in amniotic fluid and cultivated amniotic fluid cells has also been established . the classic neuroimaging findings in patients with infantile gm1gangliosidosis include thalamic hyper density on non contrast computed tomography ( ncct ) scan and hypointense signal of the thalami with persistent high signal intensity of the white matter on t2-weighted images , indicating severely defective myelination[13 ] [ figure 4 ] . significant white matter abnormalities are present only in the infantile form of gm1gangliosidosis , but they are also described in other infantile - onset neuronal storage disorders , such as gm2gangliosidosis and infantile neuronal ceroid lipofuscinosis . a paucity of myelin in gm1gangliosidosis has been demonstrated by several classical neuropathologic and neuroimaging studies of patients and animal models .