Aicardi-Goutieres syndrome

December 31, 2014

Synonyms

Overview

Aicardi–Goutières syndrome, which is completely distinct from the similarly named Aicardi syndrome, is a rare, usually early onset childhood, inflammatory disorder most typically affecting the brain and the skin (neurodevelopmental disorder).The majority of affected individuals experience significant intellectual and physical problems, although this is not always the case. The clinical features of AGS can mimic those of in utero acquired infection, and some characteristics of the condition also overlap with the autoimmune disease systemic lupus erythematosus (SLE).Following an original description of eight cases in 1984,the condition was first referred to as 'Aicardi–Goutières syndrome' in 1992,and the first international meeting on AGS was held in Pavia, Italy, in 2001.

Symptoms

The initial description of AGS suggested that the disease was always severe, and was associated with unremitting neurological decline, resulting in death in childhood.As more cases have been identified, it has become apparent that this is not necessarily the case, with many patients now considered to demonstrate an apparently stable clinical picture, alive in their 4th decade.Moreover, rare individuals with pathogenic mutations in the AGS-related genes can be minimally affected (perhaps only with chilblains) and are in mainstream education, and even affected siblings within a family can show marked differences in severity.

In about ten percent of cases, AGS presents at or soon after birth (i.e. in the neonatal period). This presentation of the disease is characterized by microcephaly, neonatal seizures, poor feeding, jitteriness, cerebral calcifications (accumulation of calcium deposits in the brain), white matter abnormalities, and cerebral atrophy; thus indicating that the disease process became active before birth i.e. in utero.These infants can have hepatosplenomegaly and thrombocytopaenia, very much like cases of transplacental viral infection. About one third of such early presenting cases, most frequently in association with mutations in TREX1, die in early childhood.

Otherwise the majority of AGS cases present in early infancy, sometimes after an apparently normal period of development.During the first few months after birth, these children develop features of an encephalopathy with irritability, persistent crying, feeding difficulties, an intermittent fever (without obvious infection), and abnormal neurology with disturbed tone, dystonia, an exaggerated startle response, and sometimes seizures.Glaucoma can be present at birth, or develop later.Many children retain apparently normal vision, although a significant number are cortically blind. Hearing is almost invariably normal. Over time, up to 40% of patients develop so-called chilblain lesions, most typically on the toes and fingers and occasionally also involving the ears.They are usually worse in the winter.

Symptoms:

Cognitive impairment
Holoprosencephaly
Hypertonia
Porencephaly

Causes

AGS is a genetically heterogeneous disease resulting from mutations in any of seven genes encoding: TREX1 - a 3-prime repair exonuclease with preferential activity on single stranded DNA (TREX1);the three non-allelic components of the RNase H2 endonuclease complex acting on ribonucleotides in RNA:DNA hybrids (RNASEH2A, RNASEH2B, RNASEH2C);a Sam domain and HD domain containing protein which functions as a deoxynucleoside triphosphate triphosphohydrolase (SAMHD1);an enzyme catalysing the hydrolytic deamination of adenosine to inosine in double-stranded RNA (ADAR1);and the cytosolic double-stranded RNA receptor MDA5 (encoded by IFIH1). Mutations in the gnee OCLN on chromosome chromosome 5q13.2, which is thought to cause band-like calcification in the brain, have been discovered in affected individuals and categorized as BLCPMG which often associated with AGS.In most cases, except for IFIH1- and rare cases of TREX1- and ADAR1-related disease, these mutations follow an autosomal recessive inheritance pattern (and thus the parents of an affected child face a 1 in 4 risk of having a further child similarly affected at every conception). Most cases are inherited in an autosomal recessive pattern, although rare autosomal dominant cases have been reported.

Diagnosis

Laboratory: normal metabolic and infective screening. An increase in the number of white cells (particularly lymphocytes) in the CSF, and high levels of interferon-alpha activity and neopterin in the CSF are important clues - however, these features are not always present. More recently, a persistent elevation of mRNA levels of interferon-stimulated gene transcripts have been recorded in the peripheral blood of almost all cases of AGS with mutations in TREX1, RNASEH2A, RNASEH2C, SAMHD1, ADAR1 and IFIH1, and in 75% of patients with mutations in RNASEH2B. These results are irrespective of age. Thus, this interferon signature appears to be a very good marker of disease.

Neuroradiology: The spectrum of neuroradiological features associated with AGS is broad, but is most typically characterised by the following:

Cerebral calcifications: Calcifications on CT (computed tomography) are seen as areas of abnormal signal, typically bilateral and located in the basal ganglia, but sometimes also extending into the white matter. Calcifications are usually better detected using CT scans (and can be missed completely on MRI (magnetic resonance imaging)).
White matter abnormalities: These are found in 75-100% of cases, and are best visualised on MRI. Signal changes can be particularly prominent in frontal and temporal regions. White matter abnormalities sometimes include cystic degeneration.
Cerebral atrophy: is seen frequently.

Genetics: pathogenic mutations in any of the seven genes known to be involved in AGS.

Treatment

Treatment is symptomatic and supportive. There is very limited information available on the use of manual treatments for Aicardi-Goutieres syndrome. After an extensive review of the information available to us, we were unable to find any information on the use of integrated neuromuscular re-education in Aicardi-Goutieres syndrome. However, chest physiotherapy can be used to treat respiratory issues. Chest physiotherapy involves drumming on the back and chest with cupped hands to loosen secretions. This form of therapy has been shown to improve outcomes of respiratory complications. In addition, stretching, poitioning and range-of-motion excercises may be beneficial to muscles and the spine.

At the moment there are no therapies specifically targeting the underlying cause of AGS. Current treatments address the symptoms, which can be varied both in scope and severity. Many patients benefit from tube-feeding. Drugs can be administered to help with seizures / epilepsy. The treatment of chilblains remains problematic, but particularly involves keeping the feet / hands warm. Physical therapy, including the use of splints can help to prevent contractures, although injections of botulinum toxin (Botox) and surgery are sometimes required. Occupational therapy can help with development, and the use of technology (e.g. Assistive Communication Devices) can facilitate communication. Patients should be regularly screened for treatable conditions, most particularly glaucoma and endocrine problems (especially hypothyroidism).