ClinVar Genomic variation as it relates to human health

This variant was determined to be likely pathogenic according to ACMG Guidelines, 2015 [PMID:25741868].

Variant summary: MFSD8 c.1235C>T (p.Pro412Leu) results in a non-conservative amino acid change located in the Major facilitator superfamily domain (IPR020846) of the encoded protein sequence. Five of five in-silico tools predict a damaging effect of the variant on protein function. The variant allele was found at a frequency of 2e-05 in 251370 control chromosomes (gnomAD). c.1235C>T has been reported in the literature in multiple individuals/families affected with Neuronal Ceroid-Lipofuscinosis (Batten Disease) and cone-rod dystrophy (e.g. Aldahmesh_2009, Di Fruscio_2015, Zare-Abdollahi_2019). These data indicate that the variant is very likely to be associated with disease. Experimental evidence evaluating an impact on protein function demonstrated the variant enhanced its proteolytic cleavage in lysosomes (Steenhuis_2012). Three ClinVar submitters (evaluation after 2014) cite the variant as pathogenic/likely pathogenic. Based on the evidence outlined above, the variant was classified as pathogenic.

For these reasons, this variant has been classified as Pathogenic. Experimental studies have shown that this missense change affects MFSD8 function (PMID: 22668694). Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) has been performed at Invitae for this missense variant, however the output from this modeling did not meet the statistical confidence thresholds required to predict the impact of this variant on MFSD8 protein function. ClinVar contains an entry for this variant (Variation ID: 1005). This missense change has been observed in individual(s) with clinical features of neuronal ceroid lipofuscinosis (PMID: 19277732; Invitae). In at least one individual the data is consistent with being in trans (on the opposite chromosome) from a pathogenic variant. It has also been observed to segregate with disease in related individuals. This variant is present in population databases (rs267607235, gnomAD 0.006%). This sequence change replaces proline, which is neutral and non-polar, with leucine, which is neutral and non-polar, at codon 412 of the MFSD8 protein (p.Pro412Leu).

The p.P412L variant (also known as c.1235C>T), located in coding exon 11 of the MFSD8 gene, results from a C to T substitution at nucleotide position 1235. The proline at codon 412 is replaced by leucine, an amino acid with similar properties. A study analyzing the functional proteolytic cleavage activity of this gene in COS-7 cells found that this variant resulted in increased proteolytic cleavage of the CLN7 protein in lysosomes presumably resulting in a non-functional protein (Steenhuis et al. Biochim Biophys Acta. 2012;1822 (10):1617-28). In another study, the p.P412L variant (referred to as c.1398C>T) was identified in a homozygous state in a consanguineous Saudi Arabian family with three affected children. The index case was a 10-year-old boy who developed progressive blindness, focal seizures with secondary generalized tonic clonic convulsions, and progressive decline in cognitive function in association with the Turkish variant of late-infantile Neuronal Ceroid Lipofuscinosis, characterized by a later age of onset and a more severe seizure phenotype (Aldahmesh et al. Neurogenetics. 2009;10:307-311). This variant was previously reported in the SNPDatabase as rs267607235. This variant was not reported in population-based cohorts in the following databases: NHLBI Exome Sequencing Project (ESP) and 1000 Genomes Project. In the ESP, this variant was not observed in 6,503 samples (13,006 alleles) with coverage at this position.This amino acid position is highly conserved in available vertebrate species. In addition, this alteration is predicted to be deleterious by in silico analysis. Based on the majority of available evidence to date, this variant is likely to be pathogenic.

Based on the classification scheme VCGS_Germline_v1.1.1, this variant is classified as pathogenic. Following criteria are met: 0102 - Loss-of-function is a known mechanism of disease for this gene. (N) 0106 - This gene is known to be associated with autosomal recessive disease. (N) 0200 - Variant is predicted to result in a missense amino acid change from proline to leucine (exon 12). (N) 0251 - Variant is heterozygous. (N) 0304 - Variant is present in gnomAD <0.01 for a recessive condition (5 heterozygotes, 0 homozygotes). (P) 0501 - Missense variant consistently predicted to be damaging by multiple in silico tools or highly conserved with a major amino acid change. (P) 0600 - Variant is located in an annotated domain or motif, (the junction btw transmembrane domain 10 and 9; PMID:19277732). (N) 0705 - No comparable variants have previous evidence for pathogenicity. (N) 0802 - Moderate previous evidence of pathogenicity. This variant has been reported as homozygous and compound heterozygous in two families with neuronal ceroid lipofuscinosis and cone rod dystrophy, respectively (LOVD, ClinVar, PMID: 19277732, PMID: 31006324). (P) 0901 - Strong evidence for segregation with disease in two families (PMID: 19277732, PMID: 31006324). (P) 1002 - Moderate functional evidence supporting abnormal protein function. Assays demonstrated that mutant protein was more readily cleaved and degraded (PMID:22668694). (P) 1208 - Inheritance information for this variant is not currently available. (N) Legend: (P) - Pathogenic, (N) - Neutral, (B) - Benign