Table 2.

Reason for disease causing mutation was not identified by standard testing. The reason “Genetic heterogeneity” was selected when the presenting phenotype was consistent with that reported due to mutations in this gene but had not been previously tested as several genes are associated with this phenotype

Reason	No. of occurrences	Genetic diagnoses
Whole gene sequencing not previously available	6	TTN
Genetic heterogeneity	5	COL6A1, COL6A3, VCP, DNM2, SLC2A1
Recent gene discovery	3	STIM1, GMPPB
Specific muscle biopsy immunoanalysis not originally performed	3	LAMA2 (2 occurrences), CAV3
Polymorphism reclassified as pathogenic	3	SGCG, CAPN3 (2 occurrences)
Mutation missed by Sanger sequencing	2	CAPN3, COL6A1 mosaic
Disease rarity	2	PIEZO2, MTM1 manifesting carrier
Atypical phenotype	2	MEGF10, DYSF
Inheritance pattern misleading	1	MYH7
Mutation missed by previous gene screening technique (DHPLC)	1	LMNA