Congenital CLN8 disease of neuronal ceroid lipofuscinosis: a novel phenotype

INTRODUCTION

CLN8 disease is one of the thirteen recognized genetic types of neuronal ceroid lipofuscinosis, a group of neurodegenerative lysosomal storage disorders, most frequent in childhood. A putative 286 amino acids transmembrane CLN8 protein with unknown function is affected. Pathological variants in the CLN8 gene were associated with two different phenotypes: variant late-infantile in individuals from many countries worldwide, and epilepsy progressive with mental retardation, appearing in Finnish and Turkish subjects.

CASE REPORT

The girl showed psychomotor delay and dementia since birth, tonic-clonic seizures, myoclonus, ataxia with cerebellar atrophy, and early death at 12 years old. Electron microscopy of the skin showed mixed GROD, curvilinear, fingerprint cytosomes and mitochondrial hypertrophy. Two pathological DNA variants in the CLN8 gene (exon 2 c.1A>G; p.?/ exon 3 c.792C>G; p.Asn264Lys) were found confirming a compound heterozygous genotype.

CONCLUSION

This case is the Latin American index for a new congenital phenotype of the CLN8 disease. The congenital phenotype has to be added to the clinical spectrum of the CLN8 disease. The suspicion of CLN8 disease should be genetically sustained in challenging cases of a neurodegenerative syndrome with psychomotor delay since birth, speech difficulty and seizures. The course includes ataxia, cerebellar atrophy, and early death.

Therapeutic approaches to the challenge of neuronal ceroid lipofuscinoses

The Neuronal Ceroid Lipofuscinoses (NCLs) are lysosomal storage diseases (LSDs) affecting the central nervous system (CNS), with generally recessive inheritance. They are characterized by pathological lipofuscin-like material accumulating in cells. The clinical phenotypes at all onset ages show progressive loss of vision, decreasing cognitive and motor skills, epileptic seizures and premature death, with dementia without visual loss prominent in the rarer adult forms. Eight causal genes, CLN10/CTSD, CLN1/PPT1, CLN2/TPP1, CLN3, CLN5, CLN6, CLN7/MFSD8, CLN8, with more than 265 mutations and 38 polymorphisms (http://www.ucl.ac.uk/ncl) have been described. Other NCL genes are hypothesized, including CLN4 and CLN9; CLCN6, CLCN7 and possibly SGSH are under study. Some therapeutic strategies applied to other LSDs with significant systemic involvement would not be effective in NCLs due to the necessity of passing the blood brain barrier to prevent the neurodegeneration, repair or restore the CNS functionality. There are therapies for the NCLs currently at preclinical stages and under phase 1 trials to establish safety in affected children. These approaches involve enzyme replacement, gene therapy, neural stem cell replacement, immune therapy and other pharmacological approaches. In the next decade, progress in the understanding of the natural history and the biochemical and molecular cascade of events relevant to the pathogenesis of these diseases in humans and animal models will be required to achieve significant therapeutic advances.