Unfortunately, some of the most prevalent symptoms of FOXG1 are inconsolable crying for the first 18-24 months of life, and sleep disturbances. The crying seems to be a sensory processing disorder. Talk to your OT about therapeutic brushing, a technique used to minimize sensory input. As for the sleeping issues, some parents have found a weighted blanket works well. When purchasing a weighted blanket, note that there is a ratio for the weight of the blanket to size of child.
Other parents have reported some success with various supplements and medications such as melatonin and ferrous sulfate (dr. prescribed). It is a good idea to find a good sleep neurologist and schedule a sleep study.
Make sure you consult your doctor before trying any medications or supplements.