AGS, or Aicardi-Goutières syndrome, is a rare genetic disorder that causes severe brain inflammation in infants and young children. The disease triggers the body’s antiviral immune response even when no virus is present, leading to chronic damage to the brain and, in many cases, the skin. Most children develop symptoms within the first year of life, though later-onset forms also occur.
How AGS Affects the Body
AGS belongs to a group of conditions called interferonopathies. Interferons are proteins your immune system releases to fight viruses. In AGS, genetic mutations cause cells to overproduce these proteins constantly, as if the body is fighting an infection that doesn’t exist. This persistent false alarm drives inflammation in the brain, spinal cord, and other organs.
The root problem lies in how cells handle their own genetic material. Normally, enzymes inside cells break down leftover bits of DNA and RNA so they don’t trigger an immune reaction. In AGS, those cleanup enzymes are faulty. Fragments of the cell’s own nucleic acids accumulate in the wrong places, and the immune system mistakes them for viral invaders. This kicks off a signaling chain that ramps up interferon production, which in turn fuels more inflammation in a self-reinforcing cycle.
Genes Linked to AGS
Seven genes are currently known to cause AGS: TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, ADAR1, and IFIH1. All of them are involved in processing or sensing nucleic acids. Over 50% of AGS patients carry mutations in the three genes that encode the RNase H2 enzyme complex, making these the most common genetic cause.
Most forms of AGS follow an autosomal recessive inheritance pattern, meaning a child must inherit a faulty copy of the gene from each parent. The exception is IFIH1, which causes AGS through a single dominant mutation that makes the immune sensor it encodes overly sensitive to RNA. These IFIH1 mutations are often spontaneous rather than inherited from a parent.
The specific gene involved can influence how the disease presents. TREX1 mutations, for example, tend to cause the most severe early-onset form with extensive white matter damage in the brain. RNASEH2B mutations are more commonly associated with later onset and delayed development of the brain’s protective myelin coating.
Symptoms in Early and Later Onset
AGS can appear in two broad patterns. In the early-onset form, signs are present at or shortly after birth. These include rapid involuntary twitching of the arms, legs, and face, feeding difficulties, an abnormally small head (microcephaly), seizures, and inflammation of the liver, brain, and spinal cord. Some infants also develop skin rashes and have enlarged livers or spleens. Because these symptoms closely resemble a congenital infection like cytomegalovirus or toxoplasmosis, early AGS is frequently misdiagnosed.
In the later-onset form, children may appear healthy for weeks or months before symptoms emerge. Parents often notice irritability, inconsolable crying, intermittent unexplained fevers, and a slowing of head growth. Muscle stiffness (spasticity) and involuntary muscle contractions (dystonia) develop progressively. Many children experience developmental regression, losing skills they had previously gained. Vision problems, feeding difficulties, and a drop in platelets (the blood cells responsible for clotting) can also occur.
One of the more distinctive features of AGS is chilblains, painful red or purple swelling on the fingers, toes, and ears that worsens in cold, damp weather. While chilblains can happen in otherwise healthy people, their presence in a young child with neurological problems is a strong clinical clue pointing toward AGS.
How AGS Is Diagnosed
Brain imaging is central to diagnosis. CT and MRI scans reveal three hallmark findings: calcium deposits in the brain, white matter abnormalities, and brain shrinkage. In a study of 121 children with confirmed AGS, calcium deposits appeared in about 91% of cases, typically as small spots in the deep brain structures and white matter. White matter abnormalities were present in over 99%, with patterns ranging from involvement of just the front and side regions to widespread damage throughout the brain. Some children with TREX1 mutations develop cysts deep within the white matter, a more recently recognized feature.
A spinal fluid analysis provides further evidence. The classic finding is an elevated white blood cell count in the cerebrospinal fluid, a sign of ongoing brain inflammation. Even more telling is the level of interferon-alpha in the spinal fluid, which was elevated on 91% of occasions tested in one large clinical study. Importantly, interferon levels can be high even when the white blood cell count looks normal, so both measures are valuable. Genetic testing confirms the diagnosis by identifying mutations in one of the seven known AGS genes.
Treatment Options
There is no cure for AGS. Treatment has historically been supportive, focusing on managing seizures, feeding difficulties, muscle stiffness, and skin symptoms. Physical therapy helps maintain mobility and comfort.
The most promising targeted approach involves JAK inhibitors, medications that block the signaling pathway downstream of interferons. A JAK1/2 inhibitor called baricitinib has been used in small clinical studies. Results show clear improvement in skin symptoms and systemic inflammation markers. Neurological outcomes, however, have been less encouraging. One real-world study found a statistically significant but minor improvement on a neurological severity scale, with no meaningful change in movement disorders or daily-life functioning. This suggests that once brain damage has occurred, blocking interferon signaling may not reverse it, though earlier treatment could potentially change that picture.
Outlook and Severity
AGS varies widely in severity depending on the gene involved and when symptoms begin. Children with early-onset TREX1 mutations tend to have the most severe course, with profound disability from infancy. Those with RNASEH2B mutations often have a milder trajectory, with some individuals retaining the ability to walk and communicate.
The disease can be fatal, particularly in the first years of life, though many individuals survive into adulthood with significant neurological impairment. Because AGS is so rare, large-scale survival statistics are limited. The condition follows a pattern common to congenital neurological disorders: a wide spectrum from severe early death to decades-long survival with varying levels of disability. Families receiving this diagnosis benefit from connecting with specialist centers experienced in interferonopathies, where care teams can coordinate neurological, immunological, and developmental support.