Alternative titles; symbols
HGNC Approved Gene Symbol: NHLRC1
Cytogenetic location: 6p22.3 Genomic coordinates (GRCh38) : 6:18,120,440-18,122,677 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 6p22.3 | Myoclonic epilepsy of Lafora 2 | 620681 | Autosomal recessive | 3 |
The NHLRC1 gene encodes malin, a single subunit E3 ubiquitin (UBB; 191339) ligase, which contains a RING-HC-type zinc finger and 6 NHL domains and is subclassified as a member of the RING-HCa family (Gentry et al., 2005).
Within an 840-kb region on chromosome 6p22.3 in which the putative EPM2B locus for Lafora disease (620681) was mapped, Chan et al. (2003) identified a single-exon gene, termed NHLRC1. The gene is predicted to encode a 395-amino acid protein, termed malin ('mal' for seizure in French), containing a zinc finger of the RING type and 6 NHL-repeat protein-protein interaction domains. The presence of the RING finger predicts an E3 ubiquitin ligase function. Northern blot analysis indicated 2 transcripts of 1.5 kb and 2.4 kb in all tissues examined, including multiple subregions of the brain. In cultured cells, malin was localized at the endoplasmic reticulum and, to a lesser extent, in the nucleus. These results were similar to those observed for laforin (EPM2A; 607566).
Chan et al. (2003) identified the NHLRC1 gene between markers D6S1688 and D6S1567 on chromosome 6p22.3.
By yeast 2-hybrid screen of a human brain cDNA library, Gentry et al. (2005) found that malin directly bound and interacted with laforin in HEK293T cells in vivo. Laforin is polyubiquitinated in a malin-dependent manner, which leads to laforin degradation. Ubiquitination depended on malin's RING domain but not on its NHL domains, whereas the NHL domains functioned as a substrate-interacting motif to bind laforin. Mutations in the NHLRC1 gene abolished both laforin polyubiquitination and degradation. Gentry et al. (2005) concluded that malin is a single-subunit E3 ligase, that laforin is a malin substrate, and that malin regulates laforin protein concentration. They further suggested that mutations in the NHLRC1 gene resulting in loss of the E3 ligase activity of malin underlie the onset of Lafora disease.
Lohi et al. (2005) showed that laforin is a GSK3B (605004) ser9 phosphatase, and therefore capable of inactivating glycogen synthase (GYS1; 138570) through GSK3. Laforin also interacted with malin, which has been shown to bind GYS1. The authors proposed that laforin, in response to appearance of polyglucosans, directs 2 negative feedback pathways: polyglucosan-laforin-GSK3-GYS1 to inhibit GYS1 activity and polyglucosan-laforin-malin-GYS1 to remove GYS1 through proteasomal degradation.
Cori disease (232400) is a glycogen storage disease characterized by deficiency of the glycogen debranching enzyme AGL (610860). Cheng et al. (2007) showed that malin interacted with mouse Agl and promoted its ubiquitination. Transfection studies in HepG2 cells showed that Agl was cytoplasmic, whereas malin was predominantly nuclear. However, after depletion of glycogen stores, about 90% of transfected cells exhibited partial nuclear Agl staining. Elevation of cAMP increased malin levels and malin/Agl complex formation. Cheng et al. (2007) concluded that ubiquitination of AGL may play a role in the pathophysiology of both Lafora disease and Cori disease.
Mittal et al. (2007) showed that laforin and malin were recruited to aggresomes upon proteasomal blockade, possibly to clear misfolded proteins through the ubiquitin-proteasome system (UPS). Garyali et al. (2009) tested this possibility using a variety of cytotoxic misfolded proteins, including the expanded polyglutamine protein, as potential substrates. Laforin and malin, together with Hsp70 (HSPA1A; 140550) as a functional complex, suppressed the cellular toxicity of misfolded proteins; all 3 members of the complex were required for this function. Laforin and malin interacted with misfolded proteins and promoted their degradation through the UPS, and they were recruited to the polyglutamine aggregates and reduced the frequency of aggregate-positive cells. Garyali et al. (2009) suggested that the malin-laforin complex is a novel player in the neuronal response to misfolded proteins.
In 34 probands with myoclonic epilepsy of Lafora, Chan et al. (2003) identified 17 different mutations in the NHLRC1 gene in 26 families (see MELF2, EPM2B; 620681), including 8 deletions, 1 insertion, 7 missense changes, and 1 nonsense change (see, e.g., 608072.0001). Eighteen families were homozygous and 8 were compound heterozygous for the mutations.
Gomez-Abad et al. (2005) identified 18 mutations, including 12 novel mutations, in the malin gene (see, e.g., 608072.0005-608072.0007) in 23 of 25 patients with Lafora disease who did not have mutations in the laforin gene. P69A (608072.0002) was the predominant mutation, identified in 14 chromosomes from 9 unrelated patients; haplotype analysis suggested a founder effect for only 2 of these families.
Singh et al. (2005) identified 6 different mutations in the NHLRC1 gene in 5 of 8 Japanese families with Lafora disease. Another Japanese family had a mutation in the EPM2A gene, and 2 Japanese families did not have mutations in either gene. Singh et al. (2005) concluded that mutations in the NHLRC1 gene are a common cause of Lafora disease in Japan.
Singh et al. (2006) identified 7 different mutations, including 2 novel mutations, in the NHLRC1 gene in affected members of 8 families with Lafora disease. The authors stated that 39 different mutations had been identified in the NHLRC1 gene.
Ianzano et al. (2005) reported the creation of a Lafora progressive myoclonus epilepsy mutation database.
More than 5% of purebred miniature wirehaired dachshunds (MWHDs) in the United Kingdom suffer an autosomal recessive progressive myoclonic epilepsy (PME), which Lohi et al. (2005) showed to be Lafora disease (620681). Using homozygosity and linkage analysis, they mapped the MWHD disease locus to canine chromosome 35, which is syntenic in its entirety to human 6p25-p21. They then cloned canine Epm2b (NHLRC1). PCR identified a repeat region in affected dogs and revealed biallelic expansion of the dodecamer repeat with 19 to 26 copies of the D sequence. Comparing the amount of Epm2b mRNA in skeletal muscle from 3 affected dogs and 2 controls with quantitative RT-PCR showed that affected mRNA levels were more than 900 times reduced. To determine whether the extra D sequence is specific to MWHDs, Lohi et al. (2005) sequenced Epm2b from 2 normal unrelated dogs from each of 128 breeds. Sixty percent of their chromosomes had 3 repeats (2 Ds and 1 T) and 40%, 2 repeats (1 D and 1 T). Almost all breeds had examples of both variants in homozygous or heterozygous state. They tested the next non-MWHD PME case to present to the clinic, a basset hound, and found a homozygous 14-copy expansion of the repeat. Lohi et al. (2005) devised a test to detect and counteract the mutant allele through controlled breeding.
Criado et al. (2012) found that Epm2b -/- mice bred normally but showed accumulation of Lafora bodies (LBs), characteristic of Lafora disease. LBs were not detected in tissues from wildtype mice at any age or in tissues from Epm2b -/- mice at postnatal day-16 (P16), but LBs were abundant in brain, heart, and skeletal muscle in Epm2b -/- mice at 3 months of age and increased progressively with time. Epm2b -/- mice also showed accumulation of laforin in brain. At P16, when no LBs were detected, laforin was mostly present in the soluble fraction of all examined tissues. Laforin was increasingly found in the insoluble fraction as Epm2b -/- mice aged. Laforin colocalized with ubiquitin and glycogen synthase at 2 distinct polyglucosan structures and accumulated in these structures. Epm2b -/- mice also exhibited compromised autophagy that was independent of activation of the Mtor (601231) pathway. Epm2b -/- mice also displayed neurologic and behavioral abnormalities.
DePaoli-Roach et al. (2012) found that Epm2b -/- mice had normal glucose disposal, insulin sensitivity, and cardiac function.
In 4 French Canadian families with myoclonic epilepsy of Lafora-2 (MELF2; 620681), Chan et al. (2003) identified a homozygous 76T-A change in the NHLRC1 gene, resulting in a cys26-to-ser (C26S) substitution in one of the 7 conserved cysteine residues critical for the zinc-binding ability of the RING finger. Haplotype analysis indicated a founder effect. Singh et al. (2006) devised a DNA-based diagnostic test to specifically screen for the C26S mutation in patients with Lafora disease.
In 3 families with myoclonic epilepsy of Lafora-2 (MELF2; 620681), Chan et al. (2003) identified a homozygous 205C-G change in the NHLRC1 gene, resulting in a pro69-to-ala (P69A) substitution. Four additional affected families had the P69A mutation in compound heterozygosity with another mutation.
Gomez-Abad et al. (2005) identified the P69A mutation in 14 chromosomes from 9 unrelated patients with Lafora disease; haplotype analysis suggested a founder effect for only 2 of these families. One patient who was homozygous for the mutation presented with hepatic failure and did not develop neurologic symptoms. The P69A mutation is located in the zinc RING finger domain of the protein.
In 2 families with myoclonic epilepsy of Lafora-2 (MELF2; 620681), Chan et al. (2003) identified a homozygous 2-bp deletion, 468_469AG, in the NHLRC1 gene. Two additional families had the deletion in compound heterozygosity with a 1-bp deletion (608072.0004), and 1 family had the deletion in compound heterozygosity with the P69A mutation (608072.0002).
In a family with myoclonic epilepsy of Lafora-2 (MELF2; 620681), Chan et al. (2003) identified a homozygous 1-bp deletion, 990G, in the NHLRC1 gene. Two other affected families had compound heterozygosity for the 1-bp deletion and the 468AG deletion (608072.0003).
In a Turkish patient with myoclonic epilepsy of Lafora-2 (MELF2; 620681), Gomez-Abad et al. (2005) identified a homozygous 793C-T transition in the NHLRC1 gene, resulting in an arg265-to-ter (R265X) substitution. The patient presented at age 13 years with myoclonic seizures.
In 2 affected members of a family from Ecuador with myclonic epilepsy of Lafora-2 (MELF2; 620681), Gomez-Abad et al. (2005) identified a homozygous 593T-A transversion in the NHLRC1 gene, resulting in an ile198-to-asn (I198N) substitution in an NHL protein-protein interaction domain. Both patients presented with partial seizures with secondary generalization at ages 5 and 14, respectively. The patient with onset at age 5 years also developed cognitive decline and was unable to attend school.
In an Italian patient with myoclonic epilepsy of Lafora-2 (MELF2; 620681), Gomez-Abad et al. (2005) identified a homozygous 923A-T transversion in the NHLRC1 gene, resulting in an asp308-to-ala (D308A) substitution. The patient presented at age 16 years with myoclonic and absence seizures and developed cognitive decline at age 18 years.
Chan, E. M., Young, E. J., Ianzano, L., Munteanu, I., Zhao, X., Christopoulos, C. C., Avanzini, G., Elia, M., Ackerley, C. A., Jovic, N. J., Bohlega, S., Andermann, E., Rouleau, G. A., Delgado-Escueta, A. V., Minassian, B. A., Scherer, S. W. Mutations in NHLRC1 cause progressive myoclonus epilepsy. Nature Genet. 35: 125-127, 2003. [PubMed: 12958597] [Full Text: https://doi.org/10.1038/ng1238]
Cheng, A., Zhang, M., Gentry, M. S., Worby, C. A., Dixon, J. E., Saltiel, A. R. A role for AGL ubiquitination in the glycogen storage disorders of Lafora and Cori's disease. Genes Dev. 21: 2399-2409, 2007. [PubMed: 17908927] [Full Text: https://doi.org/10.1101/gad.1553207]
Criado, O., Aguado, C., Gayarre, J., Duran-Trio, L., Garcia-Cabrero, A. M., Mouron, S., Juana-Lopez, L., Dominguez, M., Navarro, C., Serratosa, J. M., Sanchez, M., Sanz, P., Bovolenta, P., Knecht, E., Rodriguez de Cordoba, S. Lafora bodies and neurological defects in malin-deficient mice correlate with impaired autophagy. Hum. Molec. Genet. 21: 1521-1533, 2012. Note: Erratum: Hum. Molec. Genet. 21: 4366 only, 2012. [PubMed: 22186026] [Full Text: https://doi.org/10.1093/hmg/ddr590]
DePaoli-Roach, A. A., Segvich, D. M., Meyer, C. M., Rahimi, Y., Worby, C. A., Gentry, M. S., Roach, P. J. Laforin and malin knockout mice have normal glucose disposal and insulin sensitivity. Hum. Molec. Genet. 21: 1604-1610, 2012. [PubMed: 22186021] [Full Text: https://doi.org/10.1093/hmg/ddr598]
Garyali, P., Siwach, P., Singh, P. K., Puri, R., Mittal, S., Sengupta, S., Parihar, R., Ganesh, S. The malin-laforin complex suppresses the cellular toxicity of misfolded proteins by promoting their degradation through the ubiquitin-proteasome system. Hum. Molec. Genet. 18: 688-700, 2009. [PubMed: 19036738] [Full Text: https://doi.org/10.1093/hmg/ddn398]
Gentry, M. S., Worby, C. A., Dixon, J. E. Insights into Lafora disease: malin is an E3 ubiquitin ligase that ubiquitinates and promotes the degradation of laforin. Proc. Nat. Acad. Sci. 102: 8501-8506, 2005. [PubMed: 15930137] [Full Text: https://doi.org/10.1073/pnas.0503285102]
Gomez-Abad, C., Gomez-Garre, P., Gutierrez-Delicado, E., Saygi, S., Michelucci, R., Tassinari, C. A., Rodriguez de Cordoba, S., Serratosa, J. M. Lafora disease due to EPM2B mutations: a clinical and genetic study. Neurology 64: 982-986, 2005. [PubMed: 15781812] [Full Text: https://doi.org/10.1212/01.WNL.0000154519.10805.F7]
Ianzano, L., Zhang, J., Chan, E. M., Zhao, X.-C., Lohi, H., Scherer, S. W., Minassian, B. A. Lafora progressive myoclonus epilepsy mutation database-EPM2A and NHLRC1 (EMP2B) genes. Hum. Mutat. 26: 397 only, 2005. Note: Full article online. [PubMed: 16134145] [Full Text: https://doi.org/10.1002/humu.9376]
Lohi, H., Ianzano, L., Zhao, X.-C., Chan, E. M., Turnbull, J., Scherer, S. W., Ackerley, C. A., Minassian, B. A. Novel glycogen synthase kinase 3 and ubiquitination pathways in progressive myoclonus epilepsy. Hum. Molec. Genet. 14: 2727-2736, 2005. [PubMed: 16115820] [Full Text: https://doi.org/10.1093/hmg/ddi306]
Lohi, H., Young, E. J., Fitzmaurice, S. N., Rusbridge, C., Chan, E. M., Vervoort, M., Turnbull, J., Zhao, X.-C., Ianzano, L., Paterson, A. D., Sutter, N. B., Ostrander, E. A., Andre, C., Shelton, G. D., Ackerley, C. A., Scherer, S. W., Minassian, B. A. Expanded repeat in canine epilepsy. Science 307: 81 only, 2005. [PubMed: 15637270] [Full Text: https://doi.org/10.1126/science.1102832]
Mittal, S., Dubey, D., Yamakawa, K., Ganesh, S. Lafora disease proteins malin and laforin are recruited to aggresomes in response to proteasomal impairment. Hum. Molec. Genet. 16: 753-762, 2007. [PubMed: 17337485] [Full Text: https://doi.org/10.1093/hmg/ddm006]
Singh, S., Sethi, I., Francheschetti, S., Riggio, C., Avanzini, G., Yamakawa, K., Delgado-Escueta, A. V., Ganesh, S. Novel NHLRC1 mutations and genotype-phenotype correlations in patients with Lafora's progressive myoclonic epilepsy. J. Med. Genet. 43: e48, 2006. Note: Electronic Article. [PubMed: 16950819] [Full Text: https://doi.org/10.1136/jmg.2005.039479]
Singh, S., Suzuki, T., Uchiyama, A., Kumada, S., Moriyama, N., Hirose, S., Takahashi, Y., Sugie, H., Mizoguchi, K., Inoue, Y., Kimura, K., Sawaishi, Y., Yamakawa, K., Ganesh, S. Mutations in the NHLRC1 gene are the common cause for Lafora disease in the Japanese population. J. Hum. Genet. 50: 347-352, 2005. [PubMed: 16021330] [Full Text: https://doi.org/10.1007/s10038-005-0263-7]