Clinical findings and cytogenetic analysis of small supernumerary ring chromosomes 7: report of two new cases

The Spectrum of the Prader-Willi-like Pheno- and Genotype: A Review of the Literature

Prader-Willi syndrome (PWS) is a rare genetic syndrome, caused by the loss of expression of the paternal chromosome 15q11-q13 region. Over the past years, many cases of patients with characteristics similar to PWS, but without a typical genetic aberration of the 15q11-q13 region, have been described. These patients are often labelled as Prader-Willi-like (PWL). PWL is an as-yet poorly defined syndrome, potentially affecting a significant number of children and adults. In the current clinical practice, patients labelled as PWL are mostly left without treatment options. Considering the similarities with PWS, children with PWL might benefit from the same care and treatment as children with PWS. This review gives more insight into the pheno- and genotype of PWL and includes 86 papers, containing 368 cases of patients with a PWL phenotype. We describe mutations and aberrations for consideration when suspicion of PWS remains after negative testing. The most common genetic diagnoses were Temple syndrome (formerly known as maternal uniparental disomy 14), Schaaf-Yang syndrome (truncating mutation in the MAGEL2 gene), 1p36 deletion, 2p deletion, 6q deletion, 6q duplication, 15q deletion, 15q duplication, 19p deletion, fragile X syndrome, and Xq duplication. We found that the most prevalent symptoms in the entire group were developmental delay/intellectual disability (76%), speech problems (64%), overweight/obesity (57%), hypotonia (56%), and psychobehavioral problems (53%). In addition, we propose a diagnostic approach to patients with a PWL phenotype for (pediatric) endocrinologists. PWL comprises a complex and diverse group of patients, which calls for multidisciplinary care with an individualized approach.

Molecular cytogenetic analysis and clinical manifestations of a case with de novo mosaic ring chromosome 7

AIM

Clinical and molecular cytogenetic investigations of a newborn girl exhibiting facial dysmorphism with developmental delay.

METHODS

Phenotypic evaluation was first applied to examine the proband's developmental status. Computed tomography and colour transcranial Doppler were used then to investigate her brain structure and function. Subsequently, chromosomal abnormalities were examined by karyotyping and fluorescent in situ hybridization was performed to investigate size of fragments lost at the two distal ends of the ring chromosome 7. In addition, multicolour banding was applied to rule out structural rearrangement occurs in between the ring chromosome 7.

RESULTS

The proband was born with mosaic supernumerary ring chromosome 7, without a normal karyotype detected in the peripheral blood lymphocytes. The distal arm of chromosome 7p (at least 255 kb from the telomere) was part of an extra ring chromosome 7. In addition, the distal arm of 7q, at least 8 kb from the telomere, was missing. There was no other chromosomal rearrangement detected by multicolour banding.

INTERPRETATION

This is the 19th reported case of complete ring chromosome 7 mosaicism and the first survived case with mosaic supernumerary ring 7 without a normal karyotype detected in the peripheral lymphocytes.

Maternal heterodisomy/isodisomy and paternal supernumerary ring of chromosome 7 in a child with Silver-Russell syndrome

Silver-Russell syndrome (SRS) is clinically variable although most cases have several common signs. Different chromosomes and chromosomal regions have been associated with SRS. Maternal uniparental disomy (UPD) of chromosome 7 is responsible for 5-10% of cases, probably because of an imbalance between maternal and paternal imprinted genes and more recently maternal duplication or epimutations in the 11p15 imprinted region have been described. To date, only two patients with maternal UPD7 and a mosaic condition for a supernumerary ring 7 marker have been reported, and we here report a further case. Standard QFQ banding of lymphocytes as well as fluorescence in-situ hybridization analyses were performed to identify and characterize the supernumerary marker. UPD testing was performed on both the patient's and parents' DNA using chromosome 7 microsatellite markers. The patient demonstrated a ring in about 4% of the analysed cells. On the basis of cytogenetic and molecular results, break points were tentatively identified as 7p11.2 and 7q21. Maternal hetero-/iso-UPD and a paternal origin for the supernumerary ring were demonstrated. Clinical data comparison between our patient who has a SRS phenotype and cases with hetero-/iso-UPD7 mat and mosaicism for a paternally derived chromosome 7 ring and previously reported ring 7 cases suggest that the SRS phenotype is probably because of the UPD rather than to the partial trisomy.

Rearrangements of the Williams-Beuren syndrome locus: molecular basis and implications for speech and language development

The Williams-Beuren syndrome (WBS) locus on human chromosome 7q11.23 is flanked by complex chromosome-specific low-copy repeats that mediate recurrent genomic rearrangements of the region. Common genomic rearrangements arise through unequal meiotic recombination and result in complex but distinct behavioural and cognitive phenotypes. Deletion of 7q11.23 results in WBS, which is characterised by mild to moderate intellectual disability or learning difficulties, with relative cognitive strengths in verbal short-term memory and in language and extreme weakness in visuospatial construction, as well as anxiety, attention-deficit hyperactivity disorder and overfriendliness. By contrast, duplication results in severely delayed speech and expressive language, with relative strength in visuospatial construction. Although deletion and duplication of the WBS region have very different effects, both cause forms of language impairment and suggest that dosage-sensitive genes within the region are important for the proper development of human speech and language. The spectrum and frequency of genomic rearrangements at 7q11.23 presents an exceptional opportunity to identify gene(s) directly involved in human speech and language development.

Severe expressive-language delay related to duplication of the Williams-Beuren locus

The Williams-Beuren syndrome (WBS) locus, at 7q11.23, is prone to recurrent chromosomal rearrangements, including the microdeletion that causes WBS, a multisystem condition with characteristic cardiovascular, cognitive, and behavioral features. It is hypothesized that reciprocal duplications of the WBS interval should also occur, and here we present such a case description. The most striking phenotype was a severe delay in expressive speech, in contrast to the normal articulation and fluent expressive language observed in persons with WBS. Our results suggest that specific genes at 7q11.23 are exquisitely sensitive to dosage alterations that can influence human language and visuospatial capabilities.