Prophase analysis of ring chromosome 13--an attempt at phenotype-karyotype correlation

Early-Onset Diabetes Mellitus in a Patient With a Chromosome 13q34qter Microdeletion Including IRS2

Diabetes mellitus is a multifactorial disease caused by a complex interaction of environmental and genetic factors. Some diabetes mellitus cases, however, are caused by a limited number of mutant genes. Chromosome 13q deletion syndrome, an extremely rare genetic disorder, is caused by structural and functional monosomy of the 13q chromosomal region. We report the case of a 38-year-old Japanese man with Chr13q deletion (a mosaic pattern with heterozygous ring Chr13q) who developed diabetes mellitus. Early-onset diabetes mellitus developed in this patient because of insulin resistance and a lack of adequate insulin secretion. Microarray analysis identified a 4.8-Mb deletion of distal Chr13q, leading to a copy number loss of 40 genes. Among those genes, the insulin receptor substrate 2 gene (IRS2) was the most likely causative candidate for the development of diabetes mellitus in this patient, based on the model of IRS2 knockout mice, which have abnormal glucose and insulin homeostasis closely resembling the human diabetes phenotype. These data provide important information regarding the contribution of a microdeletion of Chr13q, including in IRS2, to the pathogenesis of diabetes mellitus in humans.

Boy with bilateral retinoblastoma due to an unusual ring chromosome 13 with activation of a latent centromere

We present a patient with bilateral retinoblastoma and developmental delay who has an abnormal male karyotype containing 47 chromosomes, including an acentric derivative chromosome 13. We postulate that the derivative 13 occurred after a break at 13q14, with the proximal portion of the chromosome forming a ring and the distal portion undergoing duplication. Thus, this patient is trisomic for 13q14-->qter. The derivative chromosome with duplicated distal portion (13q14-->qter) lacked the 13 centromere and was negative for chromosome 13 alpha-satellite DNA by low stringency FISH. Nevertheless, this chromosome is stably transmitted in lymphocytes and fibroblasts. A single primary constriction was observed at band 13q21, consistent with activation of a latent centromere (neocentromere) at this band. The neocentromere on der(13) was positive for multiple centromeric proteins, suggesting that it acts as the functional centromere. By FISH, the Rb gene was present on the normal 13, the proximally derived ring chromosome, but not on the derivative chromosome. Although there was no evidence for disruption of the Rb gene, this chromosome rearrangement most likely results in abnormal expression of the Rb gene product.

Ring chromosome 13: lack of distinct syndromes based on different breakpoints on 13q

A stillborn male child with anencephaly and multiple malformations was found to have the karyotype 46,XY,r(13) (p11q21.1). The breakpoint at 13q21.1, determined by high resolution banding, is the most proximal breakpoint ever reported in patients with ring chromosome 13. In situ hybridisation with the probe L1.26 confirmed the derivation from chromosome 13 and DNA polymorphism analysis showed maternal origin of the ring chromosome. Our results, together with a review of previous reports of cases with ring chromosome 13 with identified breakpoints, could neither support the theory of distinct clinical syndromes based on different breakpoints on 13q nor correlate the severity of symptoms with instability of the ring.

Familial t(4;13) with abnormal offspring in three generations

A newborn infant girl died at 1 day and was found to have severe intrauterine growth retardation, microcephaly, cleft lip and palate, single umbilical artery, absent thumbs, bicuspid pulmonic valve, pulmonary hypoplasia, malrotation of large and small bowel, and a 46,XX,13q+ chromosome constitution derived from a paternal t(4;13)(q25;q32) with resulting del(13q) and dup(4q). The paternal grandmother and great-grandmother also carried the balanced translocation. Each had had a child with multiple congenital anomalies including "duplex" thumbs. However, a chromosome analysis was not performed on these abnormal infants. Our patient's clinical and cytogenetic manifestations are discussed in relation to the Niebuhr map of chromosome 13.