Ring chromosome 3 in a retarded boy

Chromosome r(3)(p25.3q29) in a Patient with Developmental Delay and Congenital Heart Defects: A Case Report and a Brief Literature Review

Ring chromosome 3, r(3), is an extremely rare cytogenetic abnormality with clinical heterogeneity and only 12 cases reported in the literature. Here, we report a 1-year-old girl presenting distinctive facial features, developmental delay, and congenital heart defects with r(3) and a ∼10-Mb deletion of chromosome 3pterp25.3 (61,891-9,979,408) involving 42 known genes which was detected using G-banding karyotyping and CytoScan 750K-Array. The breakpoints in r(3) were mapped at 3p25.3 and 3q29. We also analyzed the available information on the clinical features of the reported cases with r(3) and 3p deletion syndrome in order to provide more valuable information of genotype-phenotype correlations. To our knowledge, this is the largest detected fragment described in r(3) cases and the second r(3) study using whole-genome microarray.

Clinical, cytogenetic and molecular study in a case of r(3) with 3p deletion and review of the literature

Ring chromosome 3 is a rare abnormality with only 10 patients described in the literature. We report a patient with r(3) and ∼6-Mb distal 3p deletion. Single nucleotide polymorphism array, multiplex ligation-dependent probe amplification and fluorescence in situ hybridization techniques revealed that the ring was formed by a break in 3p26.1 and fusion with the subtelomeric region of 3q. The patient presents delayed psychomotor development, growth failure, minor anomalies and other features similar to patients with 3p monosomy. The analysis of 300 metaphase cells using G-banding and fluorescence in situ hybridization with centromeric probe revealed ring instability resulting in cells with secondary aberrations and with ring loss that could also be related to some phenotypic characteristics such as growth delay. This is the first patient with r(3) studied using molecular techniques that determined the exact breakpoints in order to establish a better karyotype-phenotype correlation.

Chromosome 3p23 break with ring formation and translocation of displaced 3p23-->pter segment to 6pter

An 11 year old boy with short stature, learning difficulties, and no obvious facial anomalies has a ring (3)(p23q29) formed by a break in the short arm at 3p23 and subsequent fusion with 3qter. A second rearrangement involving translocation of the displaced 3p23-->pter segment to chromosome 6 at 6pter is non-reciprocal with no obvious loss of distal 6pter material. The involvement of one chromosome in two separate rearrangements is uncommon. The patient's relatively mild phenotype appears to be associated with the "ring syndrome" and ring instability in division rather than from any segmental aneuploidy resulting from the presence of the two rearrangements.

Loss of the 3p25.3 band is critical in the manifestation of del(3p) syndrome: karyotype-phenotype correlation in cases with deficiency of the distal portion of the short arm of chromosome 3

Two patients with monosomy for the distal portion of the short arm of chromosome 3 are described. Chromosome analysis on prometaphase cells demonstrated a karyotype of 46,XX,del(3) (p25.3) in one patient and 46,XX,r(3)(p26.1q29) in the other. The former patient showed characteristic clinical manifestations of the 3p- syndrome, including growth failure, mental retardation, microcephaly with a flat occiput, triangular face, synophrys, blepharoptosis, hypertelorism, broad and flat nose, long philtrum, down-turned mouth, micrognathia, apparently lowset and malformed ears, fingers abnormalities, and deafness. The latter patient had a nonspecific phenotype with mental retardation, growth failure and microcephaly. Karyotype-phenotype comparisons in the present cases and 16 previously reported cases with deficiency of the distal portion of 3p suggests that deficiency of the 3p25.3 band is critical to produce the main clinical manifestations of the del(3p) syndrome.

The phenotype of ring chromosome 3

A male child with mental retardation and poor growth was found to have a 46,XY,r3 (p26 leads to q29) karyotype in 92% of his peripheral lymphocytes and 90% of his cultured fibroblasts. Comparison of this patient's dysmorphic features with previously reported cases of ring 3 or deletion 3p suggests a clinical syndrome derived mainly from deletion of 3p26 leads to pter. The syndrome consists of mental retardation, pre- and postnatal growth retardation, microcephaly, hypertonia, digital anomalies, and a characteristic facies with ptosis, epicanthal folds, broad nasal root, down-turned corners of the mouth, and dysplastic ears.