With a number of hotspots, either autism and schizophrenia were observed depending on the copy-number variation (CNV) at that location.Statistical research showed that schizophrenia is more common in combination with 1q21.1 deletion syndrome. On the other side, autism is significantly more common with 1q21.1 duplication syndrome. Further research confirmed that the odds on a relation between schizophrenia and deletions at 1q21.1, 3q29, 15q13.3, 22q11.21 en Neurexin 1 (NRXN1) and duplications at 16p11.2 are at 7.5% or higher. Common variations in the BCL9 gene, which is in the distal area, confer risk of schizophrenia and may also be associated with bipolar disorder and major depressive disorder.Research is done on 10–12 genes on 1q21.1 that produce DUF1220-locations. DUF1220 is an unknown protein, which is active in the neurons of the brain near the neocortex. Based on research on apes and other mammals, it is assumed that DUF1220 is related to cognitive development (man: 212 locations; chimpanzee: 37 locations; monkey: 30 locations; mouse: 1 location). It appears that the DUF1220-locations on 1q21.1 are in areas that are related to the size and the development of the brain. The aspect of the size and development of the brain is related to autism (macrocephaly) and schizophrenia (microcephaly). It has been proposed that a deletion or duplication of a gene that produces DUF1220-areas might cause growth and development disorders in the brain Another relation between macrocephaly with duplications and microcephaly with deletions has been seen in research on the HYDIN Paralog or HYDIN2.
This part of 1q21.1 is involved in the development of the brain. It is assumed to be a dosage-sensitive gene. When this gene is not available in the 1q21.1 area, it leads to microcephaly. HYDIN2 is a recent duplication (found only in humans) of the HYDIN gene found on 16q22.2. Research on the genes CHD1L and PRKAB2 within lymphoblast cells  lead to the conclusion that anomalies appear with the 1q21.1-deletion syndrome:

CHD1L is an enzyme which is involved in untangling the chromatides and the DNA repair system. With 1q21.1 deletion syndrome a disturbance occurs, which leads to increased DNA breaks. The role of CHD1L is similar to that of helicase with the Werner syndrome
PRKAB2 is involved in maintaining the energy level of cells. With 1q21.1-deletion syndrome this function was attenuated.GJA5 has been identified as the gene that is responsible for the phenotypes observed with congenital heart diseases on the 1q21.1 location. In case of a duplication of GJA5 tetralogy of Fallot is more common. In case of a deletion other congenital heart diseases than tetralogy of Fallot are more common. References
Further reading
External links
DECIPHER database entry for 1q21.1 deletion syndrome
1q21.1 deletion, GeneReviews NCBI Bookshelf
Orpha.net