We present time-resolved spectroscopy and photometry of the dwarf nova SBSS 1108+574 , obtained during the 2012 outburst . Its quiescent spectrum is unusually rich in helium , showing broad , double-peaked emission lines from the accretion disc . We measure a line flux ratio He i 5875/H \alpha = 0.81 \pm 0.04 , a much higher ratio than typically observed in cataclysmic variables ( CVs ) . The outburst spectrum shows hydrogen and helium in absorption , with weak emission of H \alpha and He i 6678 , as well as strong He ii emission . From our photometry , we find the superhump period to be 56.34 \pm 0.18 minutes , in agreement with the previously published result . The spectroscopic period , derived from the radial velocities of the emission lines , is found to be 55.3 \pm 0.8 minutes , consistent with a previously identified photometric orbital period , and significantly below the normal CV period minimum . This indicates that the donor in SBSS 1108+574 is highly evolved . The superhump excess derived from our photometry implies a mass ratio of q = 0.086 \pm 0.014 . Our spectroscopy reveals a grazing eclipse of the large outbursting disc . As the disc is significantly larger during outburst , it is unlikely that an eclipse will be detectable in quiescence . The relatively high accretion rate implied by the detection of outbursts , together with the large mass ratio , suggests that SBSS 1108+574 is still evolving towards its period minimum .