A partial duplication of the distal segment of the long arm of chromosome 5 (q31 leads to qter) was observed in an infant with congenital malformations and dysmorphic features. The phenotypically normal father had a balanced translocation between the long arm of chromosome 5 and the short arm of chromosome 9: 46,XY,t(5;9)(q31;p24). The clinical and cytogenetic data obtained from six patients with partial duplications of two different long arm segments of chromosome 5 suggest that partial duplication of the distal long arm of chromosome 5 is associated with microcephaly, hypertelorism, epicanthus, strabismus, large upper lip, low-set, dysplastic ears, in addition to growth and psychomotor retardation. Partial duplication of the proximal part of the long arm of chromosome 5, on the other hand, is associated mainly with musculoskeletal abnormalities including muscle hypotrophy and hypotonia, scoliosis, lordosis, pectus carinatum, cubitus valgus, and genu valgum, in addition to psychomotor retardation. The dysmorphic features in this latter group include a bulging forehead, short nose, thick upper lip, low-set protruding ears and tapering, thin fingers.
Aneuploidy and structural chromosome rearrangements comprise a significant group of abnormalities in the general population. The true incidence of such abnormalities can be obtained by large research studies of consecutive newborns. In practice, the observed incidence of such chromosome abnormalities is obtained by karyotyping subjects who present for clinical reasons. The difference between the observed clinically indicated rates and the assumed rate (by comparison with data from consecutive newborn studies) would allow the estimation of the unrecognised chromosome abnormality load in the general population. The difference between these two rates would provide valuable data concerning the appropriateness of selection techniques for routine chromosome analysis. This paper reports such a study, from Queensland, Australia. A total population 5-year survey (19761980) of the diagnosed chromosome abnormalities in this unselected primary population of 2.2 million people is reported. Five hundred and eighty-nine chromosome abnormalities were detected in a consecutive series of 6092 karyotypes performed (9.7%). This figure is significantly lower than that found in most other reported series where case selection for karyotyping is determined by clinical criteria. In this current study the annual diagnostic rate for chromosome abnormalities was 5.41 per 100,000 of the general population. Cumulative frequency histograms for all types of chromosome abnormality, by age, are presented: In current practice, 32% of chromosome abnormalities are not diagnosed until adult life. Fifty percent of cases of chromosome abnormality (of all types) remain undiagnosed by the age of 1 year, in spite of a relatively liberal acceptance rate on the part of laboratories offering routine karyotyping services. It is concluded that a positive diagnostic rate greater than lo%, in routine chromosome laboratories, probably indicates that more than half the true cases of chromosome abnormality in a population are being missed.
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