Duplication of 8p23.1: a cytogenetic anomaly with no established clinical significance.

We present seven families with a cytogenetic duplication of the short arm of chromosome 8 at band 8p23.1. The duplication has been transmitted from parents to offspring in four of the seven families. In three families, the source of the extra material and its euchromatic origin were established using FISH with a YAC which was mapped to 8p23.1 and a whole chromosome paint for chromosome 8. FISH signals from this YAC were significantly larger on the duplicated chromosome compared with the normal chromosome in all six family members tested. Comparative genomic hybridisation (CGH) on a representative subject was consistent with these results. The families were ascertained for a variety of mostly incidental reasons including prenatal diagnosis for advanced maternal age. The transmission of this duplication by multiple phenotypically normal family members with no history of reproductive loss suggests the existence of a novel class of 8p23.1 duplications, which can be regarded as euchromatic variants or duplications with no phenotypic effect.

Inv(10)(p11.2q21.2), a variant chromosome.

We present 33 families in which a pericentric inversion of chromosome 10 is segregating. In addition, we summarise the data on 32 families in which an apparently identical inv(10) has been reported in the literature. Ascertainment was through prenatal diagnosis or with a normal phenotype in 21/33 families. In the other 12 families, probands were ascertained through a wide variety of referral reasons but in all but one case (a stillbirth), studies of the family showed that the reason for referral was unrelated to the chromosome abnormality. There has been, to our knowledge, no recorded instance of a recombinant chromosome 10 arising from this inversion and no excess of infertility or spontaneous abortion among carriers of either sex. We propose that inv(10)(p11.2q21.2) can be regarded as a variant analogous to the pericentric inversion of chromosome 2(p11q13). We conclude that prenatal chromosome analysis is not justified for inv(10) carriers. In addition, family investigation of carrier status is not warranted in view of the unnecessary concern this may cause parents and other family members.

Unbalanced translocation in a mother and her son in one of two 5;10 translocation families.

We present two families with different distal long arm 5;10 translocations. In one family the propositus and his mother inherited the same derived chromosome 10 from the maternal grandfather who has a balanced t(5;10)(q35.3;q26.13). The phenotype of both the affected patients is milder and only partially overlaps with that of previous cases of distal 10q deletion. Other previously reported cases of transmitted imbalance are also remarkable for mild phenotype, occurrence of deletions rather than duplications and a strong bias toward maternal as opposed to paternal transmission. In the second family, the propositus inherited a derived chromosome 10 from his mother who carries a balanced (t(5;10)(q35.1;q26.3) translocation; his clinical manifestations are consistent with an emerging phenotype for distal 5q duplications.

The parental origin of de novo X-autosome translocations in females with Duchenne muscular dystrophy revealed by M27 beta methylation analysis.

The parental origin of 3 de novo X-autosome translocations in females with Duchenne Muscular Dystrophy (DMD) was studied by means of methylation analysis using the X-linked probe M27 beta. In all three the translocation was found to be paternal in origin. The parental origin of X-autosome translocations in females with and without DMD is compared with other structural abnormalities of the X and with autosomal translocations.