Longitudinal clinical and neuro-radiological findings in a patient with leukoencephalopathy with brain calcifications and cysts (Labrune syndrome)

Expanding the Natural History of SNORD118-Related Ribosomopathy: Hints from an Early-Diagnosed Patient with Leukoencephalopathy with Calcifications and Cysts and Overview of the Literature

Leukoencephalopathy with calcifications and cysts (LCC) is a rare autosomal recessive disorder showing a pediatric or adult onset. First described in 1996 by Labrune and colleagues, it was only in 2016 that bi-allelic variants in a non-protein coding gene, SNORD118, were found as the cause for LCC, differentiating this syndrome from coats plus (CP). SNORD118 transcribes for a small nucleolar RNA, which is necessary for correct ribosome biogenesis, hence the classification of LCC among ribosomopathies. The syndrome is characterized by a combination of white matter hyperintensities, calcifications, and cysts on brain MRI with varying neurological signs. Corticosteroids, surgery, and recently bevacizumab, have been tried with unclear results since the natural history of the disease remains elusive. To date, 67 patients with a pediatric onset of disease have been described in the literature, with a clinical-radiological follow-up carried out in only eleven of them. We described the clinical-radiological follow-up from birth to almost five years of age of a late-preterm patient diagnosed with LCC and carried out a thorough overview of pediatric patients described in the literature. It is important to gather serial clinical-radiological data from other patients to depict the natural history of this disease, aiming to deeply depict genotype-phenotype correlations and make the role of new therapeutics clearer.

Leukoencephalopathy with calcifications and cysts: A case report with literature review

Leukoencephalopathy with calcifications and cysts (LCC; OMIM #614561) is a rare disease and at present there are less than 100 cases reported worldwide. Mutations in the SNORD118 gene is now known to be the cause of LCC. We present a case who was heterozygous for the n.70G>A and n.6C>T sequence variants of the SNORD118 gene, variants which to date have not been described. Compared with the cases that we reviewed, our patient had the second longest time to diagnosis (age 56) from onset of symptoms 40 years prior. Moreover, his cousin's family has a high prevalence of epilepsy. This paper reviewed all published reports to date that had descriptive cases involving LCC as well as testing for the SNORD118 gene. Since 1996 only 85 patients have been described in 59 case reports. In this review, we summarize their clinical features, especially central nervous system symptoms, treatment, pathology, and gene testing results.

Case report and discussion of pregnancy in a woman with Labrune syndrome and neurofibromatosis type 1

Labrune syndrome is a rare neurological autosomal recessive condition characterised by leukoencephalopathy, cerebral calcification and parenchymal cysts. Pregnancy has not been previously reported in an individual with this condition. This case report details the pregnancy of a primiparous woman with Labrune syndrome and neurofibromatosis type 1 who experienced a seizure in the second trimester of pregnancy, but went on to deliver her baby at term with good outcome for mother and baby. The case highlights the importance of pre-pregnancy advice in women with genetic conditions, and a multidisciplinary approach to the care of women with rare and complicated medical conditions during pregnancy.

U8 variants on the brain: a small nucleolar RNA and human disease

Small nucleolar RNAs (snoRNAs) are non-coding RNAs vital for ribosomal RNA (rRNA) maturation. The U8 snoRNA, encoded by the SNORD118 gene in humans, is an atypical C/D box snoRNA as it promotes rRNA cleavage rather than 2′–O–methylation and is unique to vertebrates. The U8 snoRNA is critical for cleavage events that produce the mature 5.8S and 28S rRNAs of the large ribosomal subunit. Unexpectedly, single nucleotide polymorphisms (SNPs) in the SNORD118 gene were recently found causal to the neurodegenerative disease leukoencephalopathy, brain calcifications, and cysts (LCC; aka Labrune syndrome), but its molecular pathogenesis is unclear. Here, we will review current knowledge on the function of the U8 snoRNA in ribosome biogenesis, and connect it to the preservation of brain function in humans as well as to its dysregulation in inherited white matter disease.

Paediatric neurosurgical implications of a ribosomopathy: illustrative case and literature review

Ribosomopathies are rare, recently defined entities. One of these, Labrune syndrome, is recognisable radiologically by its distinctive triad of leukoencephalopathy, intracranial calcifications and cysts (LCC). These cysts may have neurosurgical implications at different ages because of their progressive expansion and local mass effect. The aetiology of LCC is related to a widespread cerebral microangiopathy and is due to a genetic mutation in SNORD118, responsible for stabilisation of the large ribosomal subunit during assembly.

Neuroimaging findings in leukoencephalopathy with calcifications and cysts: case report and review of the literature

Leukoencephalopathy with cerebral calcifications and cysts (LCC) is a neurological disorder characterized by the radiological triad of white matter abnormalities, intracranial calcifications and cystic lesions variable in size resulting from a diffuse cerebral microangiopathy. Typically, progressive focal neurological deficits and seizures are the first clinical manifestation, but the severity of symptoms can vary according to the size and location of the cystic lesions holding compressive effects on the surrounding brain tissue. The most common histopathological finding is diffuse microangiopathy, which might be associated to pathogenic mutations in SNORD118 gene causing Labrune syndrome. Similar neuroradiological appearances have been found in the Coats plus syndrome, a systemic disorder caused by a genetic diffuse microangiopathy that affects not only the brain but also the retina and multiple organs, with a more complex clinical picture that address the diagnosis; biallelic mutations in CTC1 gene, encoding the conserved telomere maintenance component 1 (CTC1), are responsible of this systemic disorder. The aim of this contribution is to review the existing literature focusing on the neuroimaging characteristics by reporting cases in which radiological findings were highly suggestive for LCC.

Leukoencephalopathy with calcifications and cysts: Genetic and phenotypic spectrum

Biallelic mutations in SNORD118, encoding the small nucleolar RNA U8, cause leukoencephalopathy with calcifications and cysts (LCC). Given the difficulty in interpreting the functional consequences of variants in nonprotein encoding genes, and the high allelic polymorphism across SNORD118 in controls, we set out to provide a description of the molecular pathology and clinical spectrum observed in a cohort of patients with LCC. We identified 64 affected individuals from 56 families. Age at presentation varied from 3 weeks to 67 years, with disease onset after age 40 years in eight patients. Ten patients had died. We recorded 44 distinct, likely pathogenic, variants in SNORD118. Fifty two of 56 probands were compound heterozygotes, with parental consanguinity reported in only three families. Forty nine of 56 probands were either heterozygous (46) or homozygous (three) for a mutation involving one of seven nucleotides that facilitate a novel intramolecular interaction between the 5' end and 3' extension of precursor-U8. There was no obvious genotype-phenotype correlation to explain the marked variability in age at onset. Complementing recently published functional analyses in a zebrafish model, these data suggest that LCC most often occurs due to combinatorial severe and milder mutations, with the latter mostly affecting 3' end processing of precursor-U8.

Systemic involvement in adult-onset leukoencephalopathy with intracranial calcifications and cysts (Labrune syndrome) with a novel mutation of the SNORD118 gene

BACKGROUND AND PURPOSE

Although Labrune syndrome is a well-known disorder characterized by a typical neuroradiological triad, namely leukoencephalopathy, intracranial calcifications and cysts, there are no reports of systemic involvement in this disorder. This paper attempts to describe a peculiar clinical manifestation related to a novel mutation in the SNORD118 gene.

METHODS

Clinical examination, brain and total-body imaging, and neurophysiological and ophthalmological investigations were performed. Amplification of the SNORD118 gene and Sanger sequencing were integrated to investigate potential causative mutations.

RESULTS

A 69-year-old woman, with a long history of episodes of vertigo and gait imbalance, was referred to our hospital for progressive cognitive and motor deterioration. Computed tomography and magnetic resonance imaging disclosed diffuse bilateral leukoencephalopathy in periventricular and deep white matter, widespread calcifications and numerous cysts in the brain, liver, pancreas and kidneys. The genetic analysis revealed two biallelic variants in the SNORD118 gene, one of which is novel (n.60G>C).

CONCLUSIONS

This is the first report of adult-onset Labrune syndrome with an unusual systemic involvement presenting a novel mutation in the SNORD118 gene.

Ribosomopathies: Old Concepts, New Controversies

Ribosomopathies are a diverse subset of diseases caused by reduced expression of, or mutations in, factors necessary for making ribosomes, the protein translation machinery in the cell. Despite the ubiquitous need for ribosomes in all cell types, ribosomopathies manifest with tissue-specific defects and sometimes increased cancer susceptibility, but few treatments target the underlying cause. By highlighting new research in the field, we review current hypotheses for the basis of this tissue specificity. Based on new work, we broaden our understanding of the role of ribosome biogenesis in diverse tissue types throughout embryonic development. We also pose the question of whether previously described human conditions such as aging can be at least partially attributed to defects in making ribosomes.