Table 1.

Overview of phenotypes described in Foxp2 mutation, retinoic acid receptor (RAR) mutation and RA excess/depletion treatments.

Deficit		Foxp2 mutation		RA receptor mutation	RA excess/depletion
		Homozygous	Heterozygous
Development
	Embryogenesis defects	–	–	–	+
	Lethality	++	–	+	++
	Aberrant basal ganglia development	++	+	++	++
Cellular
	Basal ganglia cell identity defects	NT	–	+	++
	Decreased neurite growth and branching	++	NT	NT	NT
	Aberrant neuronal activity in striatum	++	++	–	+
	Unable to induce LTD	NT	++	++	NT
	Unable to induce LTP	NT	NT	++	NT
Behavior
	General motor control deficits	++	–	++	++
	Motor learning deficits	N/A	+	++	++
		(postnatal lethality)			(postnatal treatment)
	Spatial learning deficits	N/A	NT	+	+
		(postnatal lethality)

–, no effect; +, mild effect; ++, strong effect; N/A, not applicable; NT, not tested.