Cochlear implantation candidacy criteria have continued to evolve over the years, and cochlear implantation is possible with many inner-ear and brain anomalies with good hearing and linguistic outcomes. Cystic leukoencephalopathy without megalencephaly is a rare disease in children, with only 30 cases reported in the literature, but it is associated with hearing loss in only three cases. Radiological investigations can help in diagnosing this rare entity before proceeding with cochlear implantation. A four-year-old female child born out of consanguinity with normal psychomotor development, bilateral sensorineural hearing loss and an incidental magnetic resonance imaging finding of cystic leukoencephalopathy without megalencephaly underwent successful cochlear implantation. Her post-operative period was uneventful with successful mapping of the cochlear implant. This is the first reported case of cystic leukoencephalopathy without megalencephaly and with sensorineural hearing loss in which cochlear implantation was performed successfully. White matter and temporal lobe abnormalities should not deter paediatric cochlear implantation.

RNASET2 mutation has been reported in patients with cystic leukoencephalopathy without megalencephaly and the Aicardi-Goutieres syndrome. Both disorders are Mendelian mimics of congenital cytomegalovirus infection with overlapping features, including leukoencephalopathy, white matter alterations, intracranial calcification, delayed psychomotor development, intelligence disability and seizures. Only eight families with RNASET2 mutation have been previously reported. Whole exome sequencing was performed and copy number variants were described by read-depth strategy. We identified a novel nonsense variant c.128G>A (p. W43*) and a 430 Kb 6q27 microdeletion encompassing RNASET2. Our patient did not show anterior temporal lobe subcortical cysts, hearing loss, dystonia or extra-neurological features. Our results provided further genetic and phenotypic information of RNASET2 mutation in Chinese patients and highlighted the importance for physicians to consider RNASET2-related disorders when diagnosing patients with congenital brain infection-like phenotypes.

Cystic leukoencephalopathy without megalencephaly is a disorder related in some cases to RNASET2 mutations and characterized by bilateral anterior temporal subcortical cysts and multifocal lobar white matter lesions with sparing of central white matter structures. This phenotype significantly overlaps with the sequelae of in utero cytomegalovirus (CMV) infection, including the presence of intracranial calcification in some cases. Aicardi-Goutières syndrome (AGS) is another inherited leukodystrophy with cerebral calcification mimicking congenital infection. Clinical, radiological and biochemical criteria for the diagnosis of AGS have been established, although the breadth of phenotype associated with mutations in the AGS-related genes is much greater than previously envisaged. We describe the clinical, biochemical and radiological findings of five patients demonstrating a phenotype reminiscent of AGS. All patients were found to carry biallelic mutations of RNASET2. Our patients illustrate the clinical and radiological overlap that can be seen between RNASET2-related leukodystrophy and AGS in some cases. Our data highlight the need to include both disorders in the same differential diagnosis, and hint at possible shared pathomechanisms related to auto-inflammation which are worthy of further investigation.