Neuronal Ceroid Lipofuscinosis in a Domestic Cat Associated with a DNA Sequence Variant That Creates a Premature Stop Codon inCLN6

Abstract

A neutered male domestic medium-haired cat presented at a veterinary neurology clinic at 20 months of age due to progressive neurological signs that included visual impairment, focal myoclonus, and frequent severe generalized seizures that were refractory to treatment with phenobarbital. Magnetic resonance imaging revealed diffuse global brain atrophy. Due to the severity and frequency of its seizures, the cat was euthanized at 22 months of age. Microscopic examination of the cerebellum, cerebral cortex and brainstem revealed pronounced intracellular accumulations of autofluorescent storage material and inflammation in all 3 brain regions. Ultrastructural examination of the storage material indicated that it consisted almost completely of tightly-packed membrane-like material. The clinical signs and neuropathology strongly suggested that the cat suffered from a form of neuronal ceroid lipofuscinosis (NCL). Whole exome sequence analysis was performed on genomic DNA from the affected cat. Comparison of the sequence data to whole exome sequence data from 39 unaffected cats and whole genome sequence data from an additional 195 unaffected cats revealed a homozygous variant in CLN6 that was unique to the affected cat. This variant was predicted to cause a stop gain in the transcript due to a guanine to adenine transition (ENSFCAT00000025909:c.668G>A; XM_003987007.5:c.668G>A) and was the sole loss of function variant detected. CLN6 variants in other species, including humans, dogs, and sheep, are associated with the CLN6 form of NCL. Based on the affected cat's clinical signs, neuropathology and molecular genetic analysis, we conclude that the cat's disorder resulted from the loss of function of CLN6. This study is only the second to identify the molecular genetic basis of a feline NCL. Other cats exhibiting similar signs can now be screened for the CLN6 variant. This could lead to establishment of a feline model of CLN6 disease that could be used in therapeutic intervention studies.

CLN6’s luminal tail-mediated functional interference between CLN6 mutants as a novel pathomechanism for the neuronal ceroid lipofuscinoses

“…In consequence, the 132fsX mutant is likely to disturb the 239fsX mutant's structure, thereby nullifying its anti-aggregate activity. Recently, a homozygous mutation in cat CLN6 has been reported, where a guanine to adenine change (c.668G>A) creates a termination codon at Trp 223 (pTrp223Ter) (Katz et al 2020). Like human CLN6, cat CLN6 is also predicted to have seven transmembrane domains based on TMHMM, a membrane protein topology prediction program (http://www.cbs.dtu.dk/services/TMHMM/) and the Trp223 is situated in the fifth transmembrane domain (Supporting Fig.…”

Enzyme based diagnosis of type 1 and 2 neuronal ceroid lipofuscinoses

“…Table (5) showed the characteristics and laboratory findings of the 6 cases with NCL1. The clinical manifestations of the 6 cases with NCL1 showed that all the cases suffered from seizures, five out of 6 cases (83.3%) diagnosed with NCL1 had brain atrophy, regression of acquired milestones and optic problems, while 4 out of 6 cases (66.6%) had ataxia and microcephaly.…”

“…Table (5) showed the characteristics and laboratory findings of the 6 cases with NCL 2. The clinical manifestations of the 6 cases with NCL2 showed that all the cases suffered from seizures and regression of acquired milestones, five out of 6 cases (83.3%) diagnosed with NCL2 had brain atrophy, three out of 6 (50%) had ataxia and 2 out of 6 (33.3%) had optic problems, microcephaly was not evident in any of the diagnosed cases.…”

“…The NCLs are considered as lysosomal storage diorders (LSDs) because of two hallmarks: the lysosomal accumulation of ceroid lipopigments and the lysosomal presence of many NCL proteins 4 . However, the collected material in NCLs is not specific for a disease and subunit c of mitochondrial ATP synthase or sphingolipid activator proteins A and D are the principle storage materials 5 .…”

Precision medicine in cats—The right biomedical model may not be the mouse!

“…Recent WGS studies in domestic cats have implicated causal variants in novel genes, including KIF3B variants causing retinal degeneration ( OMIA 002267-9685 ), UGDH causing disproportionate dwarfism ( OMIA 000187-9685 ), and GDF7 associated with another brain dysmorphology ( OMIA 000478-9685 ), all diseases with undiagnosed human patients [ 11 – 13 ]. New models for neuronal ceroid lipofuscinosis ( OMIA 001962-9685 ; OMIA 001443-9685 ) have further utilized WGS and now WES in domestic cats [ 14 , 15 ]. Intergenic structural variation (SV) and genome organization variation are becoming more recognized as keys to gene function.…”