Ring chromosome 13 with loss of the region D13S317-D13S285: Phenotypic overlap with XK syndrome

Abstract

We report on a patient with a multiple congenital abnormalities/mental retardation (MCA/MR) syndrome including facial abnormalities, agenesis of the corpus callosum, heart defect, 1st ray anomalies of the upper limb, and ambiguous genitalia, whose phenotype overlaps a previous description of XK syndrome. The patient has a ring chromosome (13) with deletion 13q32-qter. Molecular analysis demonstrated loss of the region from D13S317 to D13S285 and a paternal origin of the anomaly.

13q Deletion and central nervous system anomalies: further insights from karyotype-phenotype analyses of 14 patients

“…In our cohort, four patients (2, 4, 5 and 6) fit into group 1, as they carry proximal deletions not extending to q32; eight patients (1,3,(7)(8)(9)(10)(11)(12) show the deletion of the entire 13q32 band (with the exception of patient 3 who lacks only the q32.1 sub-band) and are assigned to group 2; and two patients (13 and 14) seem to belong to group 3 as they carry more distal deletions exclusively involving the q33-q34 bands. Table 2 lists the clinical features indicated as being typical of patients with 13q32 deletions, 3 6 and their presence or absence in our three patient groups.…”

“…Eight of the 14 patients show CNS anomalies (including NTDs). Six have eye abnormalities, including three (patients [10][11][12] who are blind owing to microphthalmos, coloboma and hypoplasia of the optic nerve. Nine patients show facial dysmorphisms, the most frequent of which are hypertelorism (8/9 cases) and a broad and prominent nasal bridge (7/9); other minor anomalies are less frequent, such as a high and narrow palate (5/9), low-set ears (4/9) and epicanthus (4/9).…”

“…Case 10 has been previously described. 12 To define the deletion breakpoints, the patients were investigated by means of FISH, or array-CGH and FISH.…”

Duplications in addition to terminal deletions are present in a proportion of ring chromosomes: clues to the mechanisms of formation

“…For example, case 9 with a 13q deletion of 33.7 Mb died at the age of 3 years because of severe congenital anomalies,10 whereas case 8 with a 13q deletion of 4.5 Mb has moderate mental retardation but no malformations (cases 10 and 14 in Ballarati et al 9). …”

“…In one case (case 33, from Zurich), the ring chromosome was transmitted from a mildly affected mother with low mosaicism to a non-mosaic daughter, while in all the other cases the ring formation had occurred de novo. Three cases, 8 (case 14 in Ballarati et al 9), 9 (case 10 in Ballarati et al 9 and Guala et al 10) and 25 (Baumer et al 11) had already been published.…”