Hand development in trisomy 21

The aetiology of atypical bone health in individuals with Down syndrome

PURPOSE

Trisomy 21 (T21), more commonly known as Down syndrome (DS) is a genetic condition where every cell in the body has an additional copy of chromosome 21. Despite improvements in our management of DS-associated health risks, we still do not understand how T21 impacts human bone health. This is a critical area of research owing to increased life expectancy of people with DS, and the predisposition of individuals with DS to early-onset osteoporosis and osteopenia.

METHODS

We have conducted a scoping review using the methodological framework of Arksey and O'Malley (2005) which analysed the existing data on bone growth, development, maintenance and repair in T21 using the Medical Subject Headings (MeSH) terms: Trisomy 21, Down syndrome, Down's syndrome, bone development, bone growth, bone maintenance, fracture risk, osteoporosis, bone mineral density, bone strength, bone mineral content, bone formation, bone repair, osteoblast, osteoclast, osteocyte, osteomacs. A total of 31 papers were identified. After screening, 16 articles were included in full-text review.

RESULTS

There was a total of eleven in vivo animal model studies identified and included in the scoping review. Of those eleven, ten revealed a difference in bone growth and development in animal models of DS, and two found that bone maintenance and repair in animal models of DS is reduced with both studies reporting an osteoporotic bone phenotype in male and female mice. All five studies that included human participants reported impacts on bone growth and development with reduced bone growth rates and delayed bone maturation in individuals with DS. At the time of review, there were no human studies directly investigating bone maintenance and repair in individuals with DS.

CONCLUSION

We found documented evidence that T21 impacts bone growth and development, maintenance and repair in both animal models and human studies.

2-Butoxyethanol Female-Rat Model of Hemolysis and Disseminated Thrombosis: X-Ray Characterization of Osteonecrosis and Growth-Plate Suppression

We recently proposed a chemically induced rat model for human hemolytic disorders associated with thrombosis. The objective of the present investigation was to apply a noninvasive, high-magnification X-ray analysis, the Faxitron radiography system, to characterize the protracted bone damage associated with this 2-butoxyethanol model and to validate it by histopathology. Groups of female Fischer 344 rats were given 0, 250, or 300 mg of 2-butoxyethanol/kg body weight daily for 4 consecutive days. Groups were then sacrificed 2 hours or 26 days after the final treatment. The treated animals displayed a darkened purple-red discoloration on the distal tail. Histopathological evaluation, including phosphotungstic acid-hematoxylin staining of animals sacrificed 2 hours after the final treatment, revealed disseminated thrombosis and infarction in multiple organs, including bones. The Faxitron MX-20 specimen radiography system was used to image selected bones of rats sacrificed 26 days posttreatment. Premature thinning of the growth plate occurred in the calcaneus, lumbar and coccygeal vertebrae, femur, and ilium of the treated animals. Areas of decreased radiographic densities were seen in the diaphysis of the femur of all treated animals. The bones were then examined histologically and showed a range of changes, including loss or damage to growth plates and necrosis of cortical bone. No thrombi were seen in the animals sacrificed at 30 days, but bone and growth plate changes consistent with prior ischemia were noted. The Faxitron proved to be an excellent noninvasive tool that can be used in future studies with this animal model to examine treatment modalities for the chronic effects of human thrombotic disorders.

Phenotypic variability in fetuses with down syndrome: a case-control pathological evaluation

OBJECTIVES

Evaluation of morphological and morphometric characteristics of fetuses with Down syndrome based on a detailed postmortem examination and comparison of these fetuses with a control group of fetuses with normal karyotype to improve the prenatal knowledge of Down syndrome characteristics.

MATERIAL AND METHODS

A case-control study was undertaken in a tertiary referral hospital. The Down syndrome fetuses (50) were compared with chromosomally normal fetuses (47) matched for gestational age. Biometric and morphological parameters were compared.

RESULTS

The biometry of fetuses with Down syndrome differs from control fetuses only in the occipitofrontal diameter and in the nasal bone length. There were craniofacial anomalies in 96% of fetuses with Down syndrome and in 51% of fetuses with normal karyotype. With the exception of small ears, all craniofacial features analyzed were significantly different between Down syndrome fetuses and control fetuses. All extremity features of fetuses with Down syndrome were significantly different from fetuses without Down syndrome. There were 31 fetuses with Down syndrome (62%) with 55 internal anomalies. Nineteen fetuses (38.8%) showed 27 cardiac anomalies. Six fetuses had more than one anomaly. There were 18 fetuses (36%) with 28 noncardiac anomalies.

DISCUSSION

The importance of studying the morphological characteristics of fetuses with Down syndrome is the contribution to a better knowledge of fetal characteristics and probably to optimize prenatal diagnosis.

Sonographic visualization of the middle phalanx of the fetal fifth digit between 13 and 17 weeks of gestation

OBJECTIVE

To assess in utero visualization of the middle phalanx of the fifth digit (MPFD) between 13 and 17 weeks of gestation.

METHODS

This was a prospective cross-sectional study in which women attending for fetal sonographic examination between 13 + 0 and 17 + 6 weeks of gestation were evaluated for the presence of the middle phalanx of the fifth digit (MPFD). A total of 682 fetuses with normal findings on first-trimester anatomical examination were recruited. Using transvaginal multifrequency 4-8 and 5-9 MHz probes, the fifth finger was examined in both axial and lateral views until optimal visualization of the MPFD was achieved.

RESULTS

The MPFD was visualized in 14.3% (2/14) of cases at 13 weeks, 70.3% (154/219) at 14 weeks, 82.2% (240/292) at 15 weeks, 97.4% (111/114) at 16 weeks and 100% (43/43) at 17 weeks of gestation.

CONCLUSIONS

Ultrasound visualization of the MPFD gradually increases during the 13- to 17-week period. This emphasizes the limited role of non-ossification of the MPFD as a sonographic marker of Down syndrome before 17 weeks of gestation.

Fetal development of the hand, digits and digit ratio (2D:4D)

OBJECTIVE

The purpose of this study was to investigate growth patterns in human hands, digits and digit ratio (2D:4D) during the fetal period.

METHODS

The study is carried out on 161 human fetuses (83 males, 78 females) free from external pathology or malformation with ages ranging between 9 and 40 weeks of gestation. Following general external measurements, length and width of the hand, digit lengths separate for each hand was measured, hand index and the ratio of the lengths of the 2nd finger to the 4th finger (2D:4D index) was computed.

RESULTS

Means and standard deviations of the parameters with respect to gestational weeks, months and trimesters were calculated. There was a significant correlation between all parameters and gestational age (p<0.001). No significant differences were observed between sexes or sides for any of the parameters (p>0.05). 2D:4D ratio was significantly higher in females compared to males (p<0.05) and mean 2D:4D did not change with gestational age.

CONCLUSION

Detailed information of hand and digit parameters related to the fetal period will reveal the extent of biological variations of hand and digit parameters to be used in future studies. We hope that data acquired in this study will facilitate other studies on hand and digit anomalies, pathologies and variations as well as diagnoses and treatments of such conditions conducted in obstetrics, perinatology, forensic medicine and fetal pathology departments.

Short hard palate in prenatal trisomy 21

OBJECTIVE

The aim of the present study was for the first time to examine on postmortal material the total midpalatal length of the hard palate and the length of its two components (the maxillary and palatine parts) in trisomy 21 fetuses, and to compare the results to normal standards.

DESIGN

Material from 31 human fetuses with genetically verified trisomy 21 was studied. The fetuses were derived from legally induced or spontaneous abortions. Palates were, after sectioning, radiographed in lateral projection (Grenz Ray radiographic apparatus). Cephalometric measurements were performed with a digital caliper. Statistically, the length measurements for the two groups were compared, adjusting for crown rump length (CRL) through linear regression. At two specific ages (150 and 170 mm CRL), the length of the palatal components in trisomy 21 was compared to normal standards.

RESULTS

For CRL 150 mm and CRL 170 mm it appears that all three palatal lengths, total length, maxillary length, and palatinal length are significantly shorter in fetuses with trisomy 21.

CONCLUSION

The main conclusion of our study is that the total palatal length in prenatal trisomy 21 is shorter than normal and that this is due both to a shortness of the maxillary and the palatine components of the hard palate.

Comparison of fetal nasal bone assessment by ultrasound at 11-14 weeks and by postmortem X-ray in trisomy 21: a prospective observational study

OBJECTIVE

To compare nasal bone assessment by ultrasound examination at 11-14 weeks' gestation and postmortem X-ray examination in fetuses with trisomy 21.

METHODS

Twenty-one fetuses with trisomy 21 which had undergone sonographic examination at 11-14 weeks for measurement of nuchal translucency thickness and assessment of the nasal bones were examined by postmortem X-ray following termination of pregnancy.

RESULTS

The nasal bones were absent in 11/21 (52.4%) fetuses on ultrasound examination at 11-14 weeks and in 10/21 (47.6%) fetuses on X-ray examination at 14 to 25 + 5 weeks. Ultrasound and X-ray findings were discordant in 9/21 (42.9%) cases. Eight of 11 (72.7%) fetuses with absent nasal bones on ultrasound examination had a nuchal translucency thickness > 95th centile.

CONCLUSION

The high incidence of absent nasal bones in first-trimester fetuses with trisomy 21 is compatible with a developmental delay. Prior to inclusion of nasal bone assessment into risk calculation for trisomy 21, the independence of absence of nasal bones by ultrasound and increased nuchal translucency above the 95th centile at 11-14 weeks should be investigated more extensively.

A histological and radiological investigation of the nasal bone in fetuses with Down syndrome

OBJECTIVES

Previous studies of nasal bone development in Down syndrome have used radiographs or ultrasound for the detection of nasal bone length or nasal bone absence. The aim of this study was to investigate the presence and size of the nasal bones in postmortem Down syndrome fetuses by means of radiographs and histological examination.

METHODS

Thirty-three aborted human fetuses (gestational age 14-25 weeks) with Down syndrome were included. A mid-sagittal tissue block was excised from the skull base to the foramen magnum and along the lateral aspect of the spine. Radiographs of the tissue block were taken in lateral, frontal and axial projections. The length of the nasal bone was measured. The tissue blocks were cut in serial sections and stained. The crown-rump length (CRL), foot length (FL) and number of ossified bones in the hand and foot (CNO) were recorded.

RESULTS

A total of 8/33 fetuses had bilateral nasal bone absence and two had unilateral absence. In fetuses with radiographically diagnosed nasal bone absence, no nasal bone could be found histologically. The majority of the Down syndrome fetuses had CRL, FL and CNO values within the range of those for normal age-matched fetuses. Nasal bone length was normal or reduced.

CONCLUSIONS

Absence of the nasal bone was registered by postmortem examination in one-third of fetuses with Down syndrome. In some fetuses this could be a result of delayed maturation associated with Down syndrome. The phenotypic differences in nasal bone appearance may reflect genotypic differences in the Down syndrome group.

Histological investigation of the palatine bone in prenatal trisomy 21

OBJECTIVE

The purpose of the present study was to investigate the horizontal part of the palatine bone in palates from human fetuses with trisomy 21 to improve the phenotypic classification of the genotypic anomaly.

METHODS

Material from 23 human trisomy 21 fetuses was included in the study. The crown rump lengths of the fetuses ranged from 80 mm to 190 mm, corresponding to about 12 to 21 weeks of gestational age. The material was examined histologically.

RESULTS AND CONCLUSIONS

Histological examination demonstrated four different palatal phenotypes on the basis of the development of the horizontal part of the palatine bone: type I, palatine bone complete; type II, the mesial region of the horizontal part of the palatine bone is lacking; type III, complete absence of the horizontal part of the palatine bone; and type IV, auxiliary bones in the region of the transpalatine suture. This finding shows that different types of malformations may occur in the horizontal part of the palatine bone in human trisomy 21 fetuses.

Postnatal structure of the sella turcica in Down syndrome

The purpose of this study was to analyze the shape of the sella turcica in a group of patients with Down syndrome and compare the findings with those made earlier in human fetuses with Down syndrome. Profile radiographs from 78 patients (age 4 months to 50 3/12 years) were analyzed. A tracing was made of each sella turcica, and the shape was compared with that of a normal sella, including the normal growth pattern from childhood to adulthood. Sella turcica structure could be classified into three morphological types, defined as: type I, almost normal appearance; type II, deviations in the anterior wall; and type III, deviations in the floor of the sella turcica. Compared with previously registered prenatal structural deviations in the sella turcica, it can be concluded that the postnatal radiographic material reflects the prenatal findings, because type I, both prenatally and postnatally, is by far the most common, whereas the remaining types are uncommon, both prenatally and postnatally. The study confirms the relevance of prenatal investigations for postnatal diagnostics as previously documented in sella turcica analyses of prenatal and postnatal myelomeningocele cases.