Contribution of Whole-Genome Sequencing and Transcript Analysis to Decipher Retinal Diseases Associated with MFSD8 Variants.

Biallelic gene defects in MFSD8 are not only a cause of the late-infantile form of neuronal ceroid lipofuscinosis, but also of rare isolated retinal degeneration. We report clinical and genetic data of seven patients compound heterozygous or homozygous for variants in MFSD8, issued from a French cohort with inherited retinal degeneration, and two additional patients retrieved from a Swiss cohort. Next-generation sequencing of large panels combined with whole-genome sequencing allowed for the identification of twelve variants from which seven were novel. Among them were one deep intronic variant c.998+1669A>G, one large deletion encompassing exon 9 and 10, and a silent change c.750A>G. Transcript analysis performed on patients' lymphoblastoid cell lines revealed the creation of a donor splice site by c.998+1669A>G, resulting in a 140 bp pseudoexon insertion in intron 10. Variant c.750A>G produced exon 8 skipping. In silico and in cellulo studies of these variants allowed us to assign the pathogenic effect, and showed that the combination of at least one severe variant with a moderate one leads to isolated retinal dystrophy, whereas the combination in trans of two severe variants is responsible for early onset severe retinal dystrophy in the context of late-infantile neuronal ceroid lipofuscinosis.

Screening and Carrier Rate of Neuronal Ceroid Lipofuscinosis in Chihuahua Dogs in Japan.

Neuronal ceroid lipofuscinosis (NCL) is a group of rare lethal neurodegenerative lysosomal storage diseases that occur in a range of dog breeds, including Chihuahuas. Recently, a homozygous single base-pair deletion (c.846delT), which causes a frame shift generating a premature stop codon (p.Phe282Leufs13*) in the canine CLN7/MFSD8 gene, has been identified as a causative mutation for NCL in Chihuahuas. The objective of this study was to determine the frequency of the mutant allele and/or carrier rate of NCL in Chihuahuas in Japan using a newly designed real-time PCR assay. Samples of saliva were randomly collected from 1007 Chihuahua puppies during physical examinations prior to the transportation to pet shops. Screening results revealed a carrier rate of 1.29%, indicating a mutant allele frequency (0.00645) that is considered sufficiently high to warrant measures for the control and prevention of this lethal disease. The genotyping assay designed in this study could make a valuable contribution to the control and prevention of NCL.

Simultaneous Identification of Both MFSD8 and RDH12 Pathogenic Variants in a Chinese Family Affected With Retinitis Pigmentosa.

Retinitis pigmentosa (RP) is characterized by tremendous genetic and phenotypic heterogeneity. Here, we investigate the pathogeny of RP in a family to provide evidence for genetic and reproductive counseling for families. Although this pregnant woman of 8+3 weeks presented with RP, her first baby was born with RP, epilepsy, and cerebellar atrophy. The research identified a compound heterozygous mutation (c.998+3_998+6del/deletion) in the MFSD8 gene of the first born, explaining the cause of the proband's disease, which cannot explain the mother's. Then, a homozygous mutation c.343+1G > A in RDH12 of the mother was found. RT-PCR is employed to find that there is a skipping of exon 10 in MFSD8 and a 15-nucleotide retention of intron5 in RDH12. The coexistence of two independent instances of RP caused by distinct genes in one pedigree is demonstrated. Based on the diagnosis, a prenatal diagnosis performed on the fetus found that the fetus's MFSD8 is affected by the same mutation as the proband. The research underscoring the complexity of RP and the need for the combination of extensive molecular genetic testing and clinical characterization in addition expands the spectrum of MFSD8 mutations. Finally, it is expected that the family members would be prevented from reproducing children with the similar disease.

Novel in-frame deletion in MFSD8 gene revealed by trio whole exome sequencing in an Iranian affected with neuronal ceroid lipofuscinosis type 7: a case report.

BACKGROUND: The neuronal ceroid lipofuscinoses are a group of neurodegenerative, lysosomal storage disorders. They are inherited as an autosomal recessive pattern with the exception of adult neuronal ceroid lipofuscinosis, which can be inherited in either an autosomal recessive or an autosomal dominant manner. The neuronal ceroid lipofuscinoses are characterized by accumulation of autofluorescent lipopigments in the cells and one of the most important pathological manifestations is ceroid accumulation in the lysosomes. Various types of neuronal ceroid lipofuscinoses are categorized based on the clinical manifestations and the genes involved. Accumulatively, 15 different genes have been found so far to be implicated in the pathogenesis of at least nine different types of neuronal ceroid lipofuscinoses, which result in similar pathological and clinical manifestations. CASE PRESENTATION: A 5-year-old Iranian boy affected by a neurodegenerative disorder with speech problems, lack of concentration, walking disability at age of 4 years leading to quadriplegia, spontaneous laughing, hidden seizure, clumsiness, psychomotor delay, and vision deterioration at age of 5 years, which could be the consequence of macular dystrophy, was referred to us for genetic testing. Trio whole exome sequencing, Sanger validation, and segregation analysis discovered a novel in-frame small deletion c.325_339del (p.Val109_Ile113del) in MFSD8 gene associated with neuronal ceroid lipofuscinosis type 7. CONCLUSIONS: The deletion found in this patient affects the exon 5 of this gene which is the region encoding transmembrane domain. Sequencing analysis in this family has shown that the index is homozygous for 15 base pairs in-frame deletion, his uncle has normal homozygous, and his parents are heterozygous. This pattern of mutation inheritance and the signs and symptoms observed in the affected male of this family are compatible with what is described in the literature for neuronal ceroid lipofuscinosis type 7 and, therefore, suggest that the MFSD8 gene deletion found in this study is most probably the cause of disease in this family.