Table 1.
CRIM status in PCMCs and fibroblasts, and GAA mutations, in 6 patients with inconclusive PBMC CRIM status results.
| Patient | CRIM status in PBMC | CRIM status in skin fibroblasts | Predicted CRIM status based on GAA mutations | GAA mutations | |
|---|---|---|---|---|---|
| Allele 1 | Allele 2 | ||||
| 1 | Indeterminate (90 kDa band) | Negative | Negative | c.437delT (p.Met146ArgfsX7)a | c.2237G>A (p.Trp746X)b |
| 2 | Indeterminate (90 kDa band) | Negative | Negative | c.1754+2T>Ac | c.1822C>T (p.Arg608X)d |
| 3 | Indeterminate (90 kDa band) | Negative | Negative | c.2560C>T (p.Arg854X)e | c.2560C>T (p.Arg854X)e |
| 4 | Indeterminate (90 kDa band) | NA | Negative | c.2560C>T (p.Arg854X)e | c.2560C>T (p.Arg854X)e |
| 5 | Indeterminate (90 kDa band) | Positive (~110 kDa band) | Positive | c.1827delC (p.Tyr609X)f | c.2481+102_2646+31del (p.Gly828_Asn882del)g |
| 6 | Negative (60 kDa band) | NA | Positive | c.2297A>C (p.Tyr766Ser)h | c.2297A>C (p.Tyr766Ser)h |
p.Met146ArgfsX7 is predicted to create a CRIM-negative allele due to introduction of a premature stop codon. To our knowledge, this mutation has not been found in other patients.
c.2237G>A (p.Trp746X) was first reported by Beesley et al [15], and is predicted to create a CRIM-negative allele due to introduction of a premature stop codon. It was previously found in patients who were CRIM negative on fibroblast analysis [7 and 12].
To our knowledge, c.1754+2T>A has not been found in any other patients. However, we have previously identified c.1754+1G>A in a patient who was CRIM-negative on fibroblast analysis, suggesting that abolishment of this splice site could result in a CRIM-negative allele [12]
c.1822C>T (p.Arg608X) was previously reported as a “severity class A” mutation with no predicted expression of the protein [16].
c.2560C>T (p.Arg854X) is common among patients with Pompe disease of African descent [17-20]. In cDNA studies, the allele carrying this mutation was found not to be expressed [21]. Patients who are homozygous for this mutation have been reported to be CRIM negative [7, 22, 23].
1827delC (p.Tyr609X) [24] is predicted to create a CRIM-negative allele due to introduction of a premature stop codon.
p.Gly828_Asn882del is common among patients with Pompe disease of Dutch ancestry and is also found in other populations [25-30]. Previous studies show that this allele is transcribed and produces protein [12, 29].
To our knowledge, p.Tyr766Ser has not been previously reported. We have found p.Tyr766Ser in homozygosity in three patients who are CRIM-positive, but not in any CRIM-negative patients (unpublished data).
Further references and information about previously published mutations are available at www.pompecenter.nl/ (Pompe Center at Erasmus Medical Center).