Guanidinoacetate methyltransferase (GAMT) deficiency: a rare but treatable epilepsy.

Epilepsy commonly presents in childhood as part of a syndrome, and some such children may reach adult services without an underlying syndromic diagnosis. For adult neurologists taking over their care, it is often unclear how hard to search for an underlying diagnosis. The diagnostic yield may be small and such a diagnosis may not change management. Young adults with learning difficulties are also challenging to investigate, as they may not tolerate standard epilepsy tests.We present such a case in which simple tests identified a unifying diagnosis. With the new diagnosis came a new treatment that had a significant impact on seizures and quality of life.