Review of the clinical cytogenetic literature provides compelling evidence for a specific relationship between imbalance of particular chromosomes or chromosomal regions and the appearance of defined patterns of phenotypic abnormalities. In many instances, detailed phenotypic mapping has made it possible to assign portions of a phenotype to relatively small chromosome segments, which are sometimes referred to as "critical regions." However, since these regions are usually defined by a subset of the phenotypic manifestations of an aneuploidy syndrome--generally those anomalies that are regarded as most characteristic or readily observable--it is important not to fall into the trap of thinking that it is imbalance of only these regions that has deleterious effects on development and function. Thus, in Down syndrome, the presence of an extra copy of the proximal part of 21q22.3 appears to result in the typical physical phenotype--as defined principally in terms of the characteristic facial and hand anomalies and congenital heart defect--in addition to mental retardation. But, duplication of proximal 21q also affects mental development, and the regions responsible for many other aspects of the Down syndrome phenotype, including Alzheimer disease, have not been defined at all. Therefore, it remains likely that loci present on many parts of the long arm of chromosome 21 play a role in the development of the overall phenotype of Down syndrome. The immediate effect at the molecular level of an aneuploidy-caused alteration in gene dose appears to be a non-compensated commensurate change in the production of gene products.(ABSTRACT TRUNCATED AT 250 WORDS)

The consequences of chromosome imbalance.

We report on a father and daughter with a partial 9p duplication, dup(9)(p22p24). Their phenotype, albeit mild, is characteristic of partial trisomy 9p. Fluorescence in situ hybridisation (FISH) was used to characterise further and confirm the G banding finding. This is the first reported instance of trisomy 9p occurring in two successive generations. The duplicated segment in these two patients is among the smallest segments reported. Comparison of our two patients and 144 reported patients with trisomy 9p (partial or complete trisomy) suggests that the 9p22 region may be responsible for the observed phenotype in 9p duplication cases.

https://jmg.bmj.com/content/jmedgenet/33/12/1045.full.pdf

Molecular cytogenetic characterisation of the first familial case of partial 9p duplication (p22p24).

We have classified patients referred for suspicion of the Brachmann-De Lange syndrome (BDLS) into two groups using techniques of numerical taxonomy. Patients with the syndrome share an array of abnormal characteristics, and those without it have different abnormal characteristics. A group of 30 characters that best distinguish the two groups of patients was used to construct a diagnostic index. The index score is expected to divide 99% of patients into those with and without the syndrome, leaving 1% in a "zone of doubt." All 46 patients used to construct the index and 16 new patients had scores in either the BDLS or non-BDLS range and none were in the zone of doubt. A previously published index using metacarpal-phalangeal measurements, although less discriminatory, confirmed our findings in 84% of 25 patients tested, the remainder having scores in the zone of doubt for that index.

Definition and Diagnosis of the Brachmann-De Lange Syndrome

Short trunk dwarfism involving skeletal anomalies of vertebrae and ribs have been reported under various names. Both dominant and recessive and severe and mild conditions are found. We report on a patient without a severe handicap by age 3 years despite severe involvement of the thorax at birth, suggesting that a more complete classification of such anomalies is needed for counseling. We have used an objective method to classify 39 informative patients from the literature, 35 said to have a recessive disease and four a dominant one. Two patients with the costovertebral segmentation defect with mesomelia (COVESDEM) syndrome were added for comparison with our patient. The results of cluster analysis show that there are three phenotypic groups of patients. Cluster 1 contains 19 patients with a severe form of spondylothoracic dysplasia; cluster 2 includes patients with a mild autosomal recessive and a dominant type; cluster 3 groups the two sibs with the COVESDEM syndrome and our patient. One must be cautious in advising families of the prognosis for a child with severe structural chest deformity since it may not be severe from a functional point of view. More data are needed for complete discrimination between the mild autosomal recessive and dominant forms.

Spondylocostal/spondylothoracic dysostosis: The clinical basis for prognosticating and genetic counseling

We report onafather anddaughter with apartial 9pduplication, dup(9)(p22p24). Theirphenotype, albeit mild,ischaracteristic ofpartial trisomy9p.Fluorescenceinsituhybridisation (FISH)was usedtocharacterise further andconfirm theG bandingfinding. Thisisthefirst reported instance oftrisomy 9poccurring intwosuccessive generations. The duplicated segmentinthesetwopatients is among thesmallest segmentsreported. Comparison ofourtwopatients and144 reported patients withtrisomy 9p(partial orcomplete trisomy) suggests thatthe 9p22regionmay beresponsible forthe observedphenotype in 9p duplication cases. (JMedGenet 1996;33:1045-1047) mostofthese patients, thetrisomic segment was inherited fromreciprocal translocation carrier parents, withonlyasmallnumberoccurring asdenovoduplications. We describe thefirst familial instance ofpartial 9p duplication, dup(9)(p22p24), occurring intwosuccessive generations. Fluorescence insitu hybridisation (FISH)wasusedtocharacterise theconventional cytogenetic findings further. Thisis amongthesmallest reported duplicated segmentsresulting inthecharacteristic partial trisomy9pphenotype, albeit mildinourtwo patients, andtheonlyfamily witha direct duplication intwosuccessive generations. Reviewof144reported trisomy 9ppatients, and comparison ofourtwopatients specifically with 11non-translocation patients, suggests that the 9p22region mayberesponsible fortheobserved phenotype inthis syndrome.

Molecular cytogenetic characterisation ofthe first familial caseofpartial 9pduplication (p22p24)

A set of descriptors was developed and used to code patients with 4p or 9p monosomy or trisomy, "blind" as to their karyotype. Techniques of numerical taxonomy were used to classify the patients on the basis of their phenotypic resemblance. As expected, the results confirm strong phenotype-karyotype correlations. When cytogenetic interpretations are uncertain, the phenotypic findings may confirm or refute the interpretations. The approach has practical implications, providing further knowledge of phenotypic effects of specific chromosomal segments, which will aid cytogeneticists in their search for karyotypic defects. More important, the results also serve as an excellent model for developing strategies for the classification of syndromes of unknown etiology.

Formal analysis of dysmorphism: Objective methods of syndrome definition

Origin of the Supernumerary Chromosome in Trisomy 21

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Formal analysis of dysmorphism: Objective methods of syndrome definition

Origin of the Supernumerary Chromosome in Trisomy 21