Figure 1
SGCE myoclonus-dystonia: autosomal dominant transmission with reduced penetrance. The patient pedigree was simplified for privacy. The patient is indicated by the arrow. The patient’s brother and female cousin were symptomatically affected with myoclonus but did not undergo confirmatory genetic testing. The patient’s grandmother (generation I) was likely the carrier of a maternally imprinted pathogenic SGCE allele that upon transmission to generation II was again maternally imprinted and silenced. However, once paternally transmitted by the patient’s father and uncle, the autosomal dominant transmission pattern re-emerges in generation III. In generation IV, there is only a 2.5% chance each of the patient’s young daughters will be affected in their lifetime due to maternal imprinting.
Figure 2
A genetics pearl for counseling patients with SGCE myoclonus-dystonia: Penetrance of the SGCE pathogenic variant differs for children of male versus female carriers.