Partial trisomy 13q21toqter de novo due to a recombinant chromosome rec(13)dup q

Genomewide scan for nonsyndromic cleft lip and palate in multigenerational Indian families reveals significant evidence of linkage at 13q33.1-34

Nonsyndromic cleft lip with or without cleft palate (CL-P) is a common congenital anomaly with incidence ranging from 1 in 300 to 1 in 2,500 live births. We analyzed two Indian pedigrees (UR017 and UR019) with isolated, nonsyndromic CL-P, in which the anomaly segregates as an autosomal dominant trait. The phenotype was variable, ranging from unilateral to bilateral CL-P. A genomewide linkage scan that used approximately 10,000 SNPs was performed. Nonparametric linkage (NPL) analysis identified 11 genomic regions (NPL>3.5; P<.005) that could potentially harbor CL-P susceptibility variations. Among those, the most significant evidence was for chromosome 13q33.1-34 at marker rs1830756 (NPL=5.57; P=.00024). This was also supported by parametric linkage; MOD score (LOD scores maximized over genetic model parameters) analysis favored an autosomal dominant model. The maximum LOD score was 4.45, and heterogeneity LOD was 4.45 (alpha =100%). Haplotype analysis with informative crossovers enabled the mapping of the CL-P locus to a region of approximately 20.17 cM (7.42 Mb) between SNPs rs951095 and rs726455. Thus, we have identified a novel genomic region on 13q33.1-34 that harbors a high-risk variant for CL-P in these Indian families.

Characterization of a familial balanced rec(13) in a child with mild MR and his half-sibling with two structurally rearranged chromosomes 13

In this report, we describe a 7-year-old child with mild mental retardation, developmental delay, and learning disabilities. His karyotype contained a rearrangement of chromosome 13, which appeared to include a duplication of 13q31-qter and a deletion of 13p12-pter regions. The chromosomal origin of the additional material was confirmed by fluorescence in situ hybridization (FISH) using a whole chromosome painting probe specific for chromosome 13. Family studies showed that his mother carried a balanced inversion of chromosome 13 and that his half-brother carried the balanced pericentric inversion of chromosome 13 from his mother as well as another structural rearrangement involving chromosome 13 presumably from his father. The findings from this study suggested that the proband's abnormal 13 resulted from an unbalanced crossing-over between the normal and maternal inverted chromosome 13.

Phenotype-karyotype correlation in patients trisomic for various segments of chromosome 13

Analysis of clinical and cytogenetic findings taken from 62 published cases of partial trisomies of chromosome 13 showed that 15 had partial trisomy for the proximal long arm and 47 had trisomy for the distal long arm. Persistence of fetal haemoglobin (Hb F), increased projections of polymorphonuclear leucocytes (PMN), depressed nasal bridge, cleft lip/palate, and clinodactyly were more frequent in patients with proximal trisomy 13. In the distal trisomy group, the common features included haemangioma, bushy eyebrows, long curled eyelashes, prominent nasal bridge, long philtrum, thin upper lip, highly arched palate, and hexadactyly. In addition, several other features were common to both the groups, often showing inconsistency even when the same segment was in trisomy. The influence of the second aneusomy as the most likely cause for such inconsistent and overlapping phenotypes is discussed in view of the fact that 42 of 62 cases were derived from a balanced translocation carrier parent.

Pericentric inversions. Problems and significance for clinical genetics

A review is given of the incidence, cytogenetics, and biologic relevance of pericentric inversions (pii). In 251 cases in the literature and our patients, 96 different inversion forms with different breakpoints are found. Eighteen of these cases have been observed several times in unrelated families; they are classified as types. The problem of pii in the heterochromatic regions of chromosomes 1 and 9 is especially emphasized and the investigations required are pointed out. The significance of the individual pii is checked with regard to their behavior in meiosis and their phenotypical relevance. An approximately 1:1 segregation is found. Fertility, stillbirth, and rates of abortion are not statistically altered. The gonadal findings available at present in man are reported and commented on. The occurrence of aneusomic recombinants among the live offspring of carriers shows a marked dependence on the length of the relative inversion segments. Since these are distinctly below average in inversion types, they only result in recombinants in exceptional cases. Certain pointers to an above-random common occurrence of other chromosomal aberrations are not found in families with pii. A correlation between pii and clinical symptoms likewise cannot be detected. However, in this connection it is pointed out that trisomic mosaics were observed jointly with pii(9) and pii(22). The review is completed by a brief examination of the literature concerning the significance of pii in evolution.

Clinical delineation of proximal and distal partial 13q trisomy

The most relevant phenotypic features seen in both proximal and distal partial trisomy 13 have been identified from a review of 35 cases. Clinical delineation of either proximal or distal partial trisomy 13 has been demonstrated through the use of conspicuous phenotypic differences. The findings of persistent foetal Hb and increased number of nuclear projections on neutrophils are consistent findings associated with partial trisomy of a proximal segment of chromosome 13 and are diagnostic for trisomy of a partial segment of chromosome 13 that contains bands 13q12 and 13q14. The physical features of polydactyly and hemangioma have been mapped to bands 13q31 and 13q32----13qter and provide a differential diagnosis for a distal trisomic segment of chromosome 13 that may include bands 13q22----13qter. A segment of chromosome 13 has been identified that does not produce any detectable phenotypes in the triplicated state. The possible role of a triplicated 13q segment in altering expression of structural and regulatory systems elsewhere in the genome has been examined. Distinct clinical syndromes involving either a partial proximal or partial distal trisomic segment of chromosome 13 may be phenotypically defined.

Familial pericentric inversion of chromosome 13 resulting in duplication 13q22 to qter

A 10-year-old male with a recombinant (13)dup q chromosome is reported. The recombinant chromosome originated from a maternal pericentric inversion which was present in two of his four normal sibs. A segregation analysis of 60 pregnancies from which one of the parents was a carrier of inv(13) showed a significant predominance of males among the viable offspring.

Two Robertsonian translocations in a boy with mental retardation

An 8-year-old boy with mental retardation was found to be a mosaic, showing three different cell lines, 46,XY/46,XY,-21,+t(q21q21)/45,XY,-13,-21,+t(q13q21) in cultured peripheral blood cells.

Meiotic consequences of pericentric inversions of chromosome 13

A case is presented demonstrating meiotic consequences of inheritance of a pericentric inversion, inv(13)(p13q21), and suggesting, together with other similar reports reviewed, that certain manifestations (highly arched palate, long philtrum, polydactyly, microphthalmia, and capillary hemangiomata) result from duplication of the distal 13q while others (cleft lip/palate, scalp defects, congenital heart disease) result from duplication of the proximal 13q.