Al-rich Al-Ge solid solutions synthesized under high pressure demonstrate physical properties strikingly different from those of pure Al. In particular, enhanced superconductivity temperature (T c ), anomalies in the phonon spectra and decrease of the Debye temperature have been observed. We show from first-principles, based on calculations of the electronic spectra and Fermi surfaces of Al-Ge substitutional solid solutions, that an electronic topological transition (ETT) takes place in the system. We predict anomalies in transport properties to be revealed experimentally for Al-Ge solid solutions with the Ge concentration ~10at.%. The influence of the ETT on the thermodynamic properties of the system is discussed and, in particular, concentration dependence of the Debye temperature is reproduced in good agreement with experiment.