AGS typically has onset in the first year of life, usually at the age of around four months. Early symptoms include irritability, feeding difficulties, sleep disturbances and recurrent fevers in the absence of any evidence of infection. They are frequently accompanied by a slowing of head growth, and thus microcephaly. In addition, children often show an increasingly apparent psychomotor delay and/or a loss of early acquired skills.
In a smaller percentage of children, the disease manifests itself in the neonatal period, the picture in these cases being characterised by neurological symptoms and increased dimensions of the liver and spleen (hepatosplenomegaly), together with signs of dysfunction of these two organs, namely anaemia, reduction of the number of platelets in the blood (thrombocytopenia) and raised transaminases. In these cases, the cerebral calcifications and the microcephaly are sometimes already present at birth.
After this initial stage, the disease tends to become stable and not show any further progression.
During or immediately after the onset phase, the neurological signs typical of AGS progressively appear. Affected subjects generally show both pyramidal and extrapyramidal signs and a picture of spastic-dystonic tetraplegia, often associated with abnormal eye movements.
Another typical finding is the presence of the “startle reaction” in response to even mild sensory (acoustic or tactile) stimuli. Some patients show epileptic seizures and EEG abnormalities: it can sometimes be difficult to distinguish between episodes of an epileptic nature and the abovementioned startle reactions.
Aicardi-Goutières syndrome presents a certain clinical heterogeneity, as there have been descriptions of late-onset cases with an atypical age at onset (after the age of 1 year). In these subjects the clinical picture is less severe, being characterised by the conservation of some motor skills and by relative preservation of intellectual function.
Some patients have extraneurological signs, the most common being transitory chilblain-like skin lesions affecting the hands, feet and ears (erythematous and desquamative, with swelling of the fingers and toes).
Other clinical features, less frequent but nevertheless described in the literature, include: hypothyroidsm, insulin-dependent diabetes mellitus, transitory antidiuretic hormone deficiency, glaucoma.