Submission Details

The relationship between ANO5 and limb girdle muscular dystrophy (LGMD; also known as LGMDR12 (LGMD2L)), inherited in the autosomal recessive pattern, has been evaluated using the ClinGen Clinical Validity Framework as of July 2020. This association was made using case-level and experimental data. The ANO5 gene is located on chromosome 11p14.3, spanning 90kb. The reference transcript, NM_213599.3, is 86.7kb long with 22 exons encoding a 913-amino acid protein. More than 70 pathogenic and likely pathogenic variants reported in humans with autosomal recessive LGMD are recorded in ClinVar and LOVD, ranging from small deletions and duplications, nonsense, frameshift and splicing to missense variants. Limb girdle muscular dystrophy is characterized by progressive weakness in muscles including, but not limited to, the proximal muscles of the pelvic and shoulder girdle, which can lead to difficulty walking. It is also accompanied by an elevated serum creatine kinase. ANO5 has been reported in association with autosomal recessive LGMD as early as 2010 by Bolduc et al (PMIDs: 20096397). Summary of Case Level Data (12 points): The association is seen in at least 6 probands in 5 publications (PMIDs: 20096397, 21820307, 22336395, 21186264, 25891276). Variants in this gene segregated with disease in 7 additional family members. More case-level evidence is available in the literature (PMIDs: 22402862, 22980763, 22742934, 22499103, 23041008, 26627873, 29970176, 21739273, 27854218, 25864073, 23670307, and others), but the maximum score for genetic evidence (12 pts) has been reached. The mechanism for disease has been reported to be biallelic loss-of-function. Summary of Experimental Data (6 points): This gene-disease relationship is supported by animal models, expression studies, functional assays and rescue evidence. ANO5 is a transmembrane protein highly expressed in muscles (PMIDs:15124103, 17418107, 28489263), mostly localized in intracellular vesicles in muscle cells (PMID:17418107, 22075693). However, a transient localization of ANO5 at plasma membrane cannot be excluded since a small fraction of ANO5 is trafficked to the plasma membrane in heterologous systems (PMID:29124309, 30257928). Even though the exact function of ANO5 is not clear, it has been shown to play a role in muscle cell membrane repair possibly through its phospholipid scrambling activity (PMID:30257928, 20096397, 26911675, 31341644, 26667038, 28559311). Several studies reported rescue of membrane repair and phospholipid scramblase defects in muscle cells from patients and animal models (PMIDs:31341644, 30257928). ANO5 co-localizes with CAV3, another protein associated with muscular dystrophy (PMID:32736698). Two different lines of mice with complete absence of ANO5 do not have any muscle defect (PMIDs:26693275, 26667038), while three animal models with truncating mutations show a muscular dystrophy phenotype (PMIDs: 29789544, 26911675, 30712070). In summary, the ANO5-autosomal recessive limb-girdle muscular dystrophy gene-disease relationship is definitive. This has been repeatedly demonstrated in both research and clinical diagnostic settings. This classification was approved by the ClinGen Limb-Girdle Muscular Dystrophy GCEP on 09/09/20 (SOP Version 7).

This gene curation was re-approved and published on 11/14/24 by the Muscular Dystrophies and Myopathies GCEP to reflect the change in the panel's name from LGMD GCEP to MDM GCEP. As part of this process, the genetic evidence was re-scored in accordance with SOP version 11.

Lumping & Splitting Consideration: OMIM disease entities: Miyoshi muscular dystrophy 3 (613319); Muscular dystrophy, limb-girdle, autosomal recessive 12 (611307); Gnathodiaphyseal dysplasia (166260). Per criteria outlined by the ClinGen Lumping and Splitting Working Group, we found no difference in molecular mechanisms AND inheritance pattern AND phenotypic variability between Miyoshi muscular dystrophy 3 and Muscular dystrophy, limb-girdle, autosomal recessive 12. Therefore, these two disease entities have been lumped into one disease entity, autosomal recessive limb girdle muscular dystrophy (MONDO:0015152). Due to differences in molecular mechanisms AND inheritance pattern, Gnathodiaphyseal dysplasia disease entity was split from the two disorders involving muscular dystrophy. Gene-Disease association between Gnathodiaphyseal dysplasia and ANO5 will be curated by a different GCEP.