Clinical Utility of Testing

Molecular testing is valuable in uncovering UPD as an explanation for imprinting disorders and some recessive diseases. Testing is typically performed for diagnostic purposes on infants, children, or adults when UPD is suspected. Prenatal testing is indicated when confined placental mosaicism is detected. In addition to the clarity a diagnosis brings in most situations, genetic counseling and risk assessments for disorders caused by UPD are greatly affected because recurrence risks are quite different in UPD situations. The recurrence risk for UPD is negligible (<1%) except for that caused by the presence of balanced translocations carried by a parent (perhaps unknown to the parent). Recurrence risks in these situations may be as high as 25%. Uniparental disomy testing after an observation of confined placental mosaicism also

PEGl/MEST 7q32

IGF2, H19, P57KIP2, KVLQT

unknown

11p15

Maternal Paternal

Maternal unknown

Paternal

SNRPN, ZNF127, FZN127, IPW, NDN, PAR1, PAR5 UBE3A

15q11-q13 Maternal

15q11-q13 Paternal unknown

Maternal allows informed reproductive choices or may prepare parents for the birth of an affected child.

UPD involving most chromosomes does not cause obvious abnormalities related to imprinting defects, as only a few chromosomes (6,7,11,14, and 15) are known to contain genes that undergo imprinting. Of these, maternally imprinted genes are present on chromosomes 7,14, 15 and 16, while paternally imprinted genes are contained on chromosomes 6, 11, 14, and 15. Maternally imprinted genes also are suspected, but not confirmed, to be present on chromosomes 2 and 16. No cases are known of either maternal or paternal UPD for chromosomes 3,12,18, or 19. In addition, neither paternal UPD for chromosomes 4,9, or 10, nor maternal UPD for chromosomes 5 or 11, has been reported. Paternal UPD for both the X and Y chromosomes together can only be heterodisomic, of paternal origin, and detected when a paternal X-linked recessive disease is inherited from the father. For many chromosomes, too few examples have been observed to determine a possible phe-notype related to UPD.

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