Partial deletion of distal 17q

A 2.3Mb deletion of 17q24.2-q24.3 associated with 'Carney Complex plus'

We present a 12-year-old with a de novo interstitial deletion of approximately 2.3Mb in chromosome band 17q24.2-q24.3, which was identified by array CGH. The most characteristic features in this case are posterior laryngeal cleft and the presence of numerous freckles and lentigines in childhood. Growth restriction, microcephaly and moderate mental retardation are also prominent features but are frequently seen with other chromosomal anomalies. The microdeletion causes haploinsufficiency of PRKAR1A (protein kinase, cAMP-dependent, regulatory 1alpha), which is known to cause Carney Complex but this diagnosis alone does not account for all of her problems and she therefore has 'Carney Complex plus'. This report illustrates the practical benefits associated with a clear cytogenetic diagnosis, as regular endocrinological and cardiac screening is required.

Mild phenotype in two siblings with distal monosomy 12p13.31-->pter

We report two sibs with trisomy for the region 2p25.1--> pter and monosomy for the region 12p13.31--> pter, due to adjacent-1 segregation of a maternal balanced reciprocal translocation, 46,XX,t(2;12)(p25.1;p13.31). These sibs presented with a mild phenotype, but nevertheless showed features of each of the contributing aneusomies. Monosomy 12p has previously been considered to have a variable and indistinct phenotype. Comparison of these patients with previous reports showed that many features, including microcephaly, facial dysmorphia, developmental and growth delay and dental and digital anomalies are frequently associated with monosomy for 12p. Many of these features are common to other aneusomies, thereby mitigating against a distinct 12p monosomy syndrome at this time. However, the combination of digital and dental anomalies may suggest the presence of this particular monosomy. The proband and his sister had some of the more non-specific features of 2p trisomy syndrome, and comparison with previous reports suggested that the characteristic 2p trisomy syndrome is more usually associated with larger or more proximal trisomies of 2p.

Del(18p) shown to be a cryptic translocation using a multiprobe FISH assay for subtelomeric chromosome rearrangements

We have previously described a fluorescence in situ hybridisation (FISH) assay for the simultaneous analysis of all human subtelomeric regions using a single microscope slide. Here we report the use of this multiprobe FISH assay in the study of a patient whose karyotype was reported by G banding analysis as 46,XX,del(18)(p11.2). Although the proband had some features suggestive of a chromosomal abnormality, relatively few of the specific features of del(18p) were present. She was a 37 year old female with mild distal spinal muscular atrophy (SMA), arthritis of the hands, an abnormal chest shape (pectus excavatum), and an unusual skin condition (keratosis pilaris). Reverse chromosome painting with degenerate oligonucleotide primer-polymerase chain reaction (DOP-PCR) amplified del(18p) chromosomes as a probe confirmed the abnormality as del(18p), with no evidence of any other chromosome involvement. Subsequently, the multiprobe FISH assay confirmed deletion of 18p subtelomeric sequence. However, the assay also showed that sequences corresponding to the 2p subtelomeric probe were present on the tip of the shortened 18p. The patient is therefore monosomic for 18p11.2-pter and trisomic for 2p25-pter, and the revised karyotype is 46,XX,der(18)t(2;18)(p25; p11.2). We believe that a proportion of all cases reported as telomeric deletions may be cryptic translocations involving other chromosome subtelomeric regions. Further studies such as this are necessary to define accurately the clinical characteristics associated with pure monosomy in chromosomal deletion syndromes.

Trisomy 2p: analysis of unusual phenotypic findings

We present three probands with partial trisomies 2p21-23 due to ins(4;2)(q21;p21p23) pat, 2p23-pter due to t(2;4)(p23;q35)mat, and 2p21-pter due to t(2;11)(p21;q23.3)mat. More than 50 cases of partial trisomy 2p have been reviewed and some abnormalities, unusual for most other types of structural autosomal imbalance, have been found in patients with inherited forms of 2p trisomy and in their non-karyotyped sibs. Neural tube defects (anencephaly, occipital encephalocele, and spina bifida) were found in five probands and 4/6 affected non-karyotyped sibs. The only triplicated segment common to all was 2p24. Different forms of "broncho-pulmonary a/hypoplasia" (including two cases of lung agenesis) were described in four patients (overlapping triplicated segment was 2p21-p25). Three patients (with overlapping triplicated segment 2p23-p25) had diaphragmatic hernia. Abnormal rotation of the heart or L-transposition of large vessels (with or without visceral heterotaxia) was found in two infants (overlapping triplicated segment 2p23-p24). In two patients with common triplicated segment 2p22.3-p25, neuroblastoma has been described. The occurrence of all these defects may be explained either by the action of the same gene(s) mapped to 2p24 or by action of some independent factors located in different segments of the short arm. Although the latter hypothesis is much less probable, it can not be rejected at the present time. We propose the existence of a genetic system controlling surveillance of an abnormal embryo to explain the phenotypic differences between patients with the same imbalance within a family. In some "restrictive" combinations the abnormal embryos will die, although in "permissive" combinations they can survive.

Campomelic dysplasia and autosomal sex reversal caused by mutations in an SRY-related gene

Induction of testis development in mammals requires the presence of the Y-chromosome gene SRY. This gene must exert its effect by interacting with other genes in the sex-determination pathway. Cloning of a translocation chromosome breakpoint from a sex-reversed patient with campomelic dysplasia, followed by mutation analysis of an adjacent gene, indicates that SOX9, an SRY-related gene, is involved in both bone formation and control of testis development.

Assignment of an autosomal sex reversal locus (SRA1) and campomelic dysplasia (CMPD1) to 17q24.3-q25.1

We have mapped the autosomal sex reversal locus, SRA1, associated with campomelic dysplasia (CMPD1) to 17q24.3-q25.1 by three independent apparently balanced de novo reciprocal translocations. Chromosome painting indicates that the translocated segment of 17q involves about 15% of chromosome 17 in all three translocations, corresponding to a breakpoint at the interphase between 17q24-q25. All three 17q breakpoints were localized distal to the growth hormone locus (GH), and proximal to thymidine kinase (TK1). Due to the distal location of the breakpoints, previously mentioned candidate genes, HOX2 and COL1A1, can be excluded as being involved in CMPD1/SRA1. The mouse mutant tail-short (Ts) which maps to the homologous syntenic region on mouse chromosome 11, displays some of the features of CMPD1.

A de novo translocation t(3;17)(q26.3;q23.1) in a child with Cornelia de Lange syndrome

A female infant with Cornelia de Lange syndrome and severe limb reduction defects is described. Chromosome analysis showed a de novo translocation with breakpoints at 3q26.3 and 17q23.1. This is the first reported case of a de novo translocation associated with this syndrome.

Miller-Dieker syndrome with ring chromosome 17

A girl presented at 6 weeks of age with failure to thrive and arching of the back. She had various dysmorphic features, hepatosplenomegaly, and developmental delay. The electroencephalogram and cranial ultrasound were abnormal, and a computed tomogram showed lissencephaly and apparent agenesis of the corpus callosum. Because of frequent aspiration she became oxygen dependent. She later developed intractable convulsions and died at the age of 9 months.