Given that mosaic Cdkn1c-MADM-7 mice (all cells are Cdkn1cflox/+) with heterozygous Cdkn1c deletion in Emx1+ lineage show microcephaly similar like cKO-Cdkn1c-MADM-7 mice, we conclude that the growth-promoting function of Cdkn1c is also highly dosage sensitive. The gene discussed is CDKN1C; the disease is microcephaly.