Euchromatic 16p + heteromorphism: First report in North America

Abstract

A heteromorphism of the short arm of 16 (16p+) was discovered in 2 unrelated infants. By G banding, the euchromatic variant appears as a light and a medium dark band just distal to the centromere. This results in an increase of the short arm by about 1/3. The same variant was present in the normal father and the normal paternal grandmother in one family and mildly retarded mother in the 2nd family. The anomalies of the 2 infants are not similar and are apparently unrelated to the 16p+ variant. Though the discovery of such euchromatic variants is highly significant for clinical diagnosis, their genetic significance and mode of origin remain to be elucidated.

Duplication of chromosome region (16)(p11.2 → p12.1) in a mother and daughter with mild mental retardation

“…Behavioral abnormalities, however, were also present in this young patient. A proximal duplication in the short arm of chromosome 16 that in phenotypically normal individuals is segregating as a polymorphism is reported by Thompson and Roberts [1987], Pinel et al [1988], Thompson et al [1990], Bryke et al [1990], Jalal et al [1990], Croci et al [1991], and Barber et al [1999]. Barber et al [1999] reported that a pseudogene cassette for the 16p11.2-specific non-functional immunoglobulin heavy chain segments and the pseudogenetic 16p11.2 creatine transporter region underlie this euchromatic variation of chromosome 16p.…”

“…In contrast to our FISH results that showed two fluorescent spots on the aberrant chromosome 16, Barber et al [1999] reported only one fluorescent spot with enhanced hybridization on the extra material. Jalal et al [1990] report on two patients with an enlarged short arm of chromosome 16. Patient 1 was referred for genetic evaluation because of macrocephaly and hypospadia.…”

“…The second patient Jalal et al [1990] report is a 12-month-old boy. This patient and his mother both have a proximal duplication of 16p that Jalal et al [1990] interpret as a variant.…”

“…16p13.2 appears to lead to the specific trisomy 16p syndrome. Furthermore, a proximal duplication in the short arm of chromosome 16 is known which in phenotypically normal individuals is segregating as a polymorphism [Thompson and Roberts, 1987;Pinel et al, 1988;Bryke et al, 1990;Jalal et al, 1990;Thompson et al, 1990;Croci et al, 1991;Barber et al, 1999]. In the present study the clinical and cytogenetic findings of a 6-yearold child with mild mental retardation and her mother are reported.…”

Rapid identification of a small dicentric supernumerary marker derived from chromosome 16 with a modified FISH technique on amniotic fluid

“…Some cases with an euchromatic 16p+ heteromorphism have been reported in patients with normal phenotype (Bryke et al, 1990;Jalal et al, 1990;Bogart et al, 1991;Ste Âphane and Genevie Áve, 1999). Although more investigations are needed, it seems that the chromosome 16 presents some pericentromeric regions whose partial trisomy has no phenotypical effect and this would help future genetic counselling when a de novo marker derived from this chromosome is found.…”