Down syndrome--a disruption of homeostasis

An anatomical study of a duplication 6p based on two sibs

Dup (6p) patients have a peculiar facial appearance (frontal bossing, hypotelorism, hypoplastic midface), low birthweight, cardiovascular defects, small kidneys, and psychomotor retardation. We thought that a detailed anatomical dissection would more precisely define the syndrome, which has been developed from clinical evaluations and autopsy reports. Our patient, a female adolescent, died at 17 11/12 years and is the oldest patient with this syndrome to be described. The brain and skull showed the greatest number of abnormalities. The brain was smaller than normal and abnormally shaped. Many of the skull abnormalities, including shortened basisphenoid/basiocciput, reduced size of cranial fossae, and steep orbital roofs, may be attributed to the brain's shape. There were no olfactory bulbs, and only one rudimentary olfactory tract was present. Other findings were the following: a high interventricular septal defect and right ventricular hypertrophy, absence of uterus and vagina, hypoplastic ovaries, a common mesentery, two left extensor indicis bellies, bilateral absence of palmaris brevis and of peroneus tertius. Our results are compared with anomalies found in other aneuploidy syndromes. Variations in some organ systems may be similar to those whose presence Shapiro [1983] has attributed to amplified developmental instability. Relationships between the brain shape and size and skull abnormalities are also discussed. From 16 reported cases, a detailed autopsy report of the affected brother, and our anatomical findings, we suggest that this syndrome may also be characterized by arhinencephaly, common mesentery, absent uterus in the female, and growth retardation in those surviving the neonatal period.

Increased adhesiveness of trisomy 21 cells and atrioventricular canal malformations in Down syndrome: a stochastic model

Based on the finding that fetal trisomy 21 fibroblasts explanted from lungs and endocardial-cushion-derived structures appear more adhesive in vitro than those from normal control individuals, we present a stochastic model for atrioventricular (AV) canal malformations in Down syndrome (DS). Computer simulations were performed to model the normal anatomic sequences of cushion-to-cushion and cushion-to-septum fusion in AV canal development. In these simulations, random-walking endocardial cells were allowed to migrate, divide, and adhere with programmable probabilities. Low values of intercellular adhesiveness engendered simulations resembling normal AV canal development; higher values of adhesiveness yielded deficiencies of AV canal development as seen in DS. Moderately high levels of adhesiveness resulted in abnormalities in only a proportion of multiple, independently performed simulations. The model successfully predicts the temporospatial sequence of anatomic events in cushion-to-septum fusion, clinical variability among individuals with the same genotype based on chance alone, and amplified developmental instability as observed in individuals with DS.

The phenotypic and cytogenetic spectrum of partial trisomy 9

A new patient with trisomy for the chromosome segment 9pter----q22 is compared to 19 previously reported cases of partial trisomy 9. Manifestations such as microcephaly, prominent nasal root, bulbous nose, and down-turned corners of the mouth are common to patients with trisomic segments extending from 9p21 to 9q13, while intra-uterine growth retardation, cleft lip/palate, skeletal anomalies, and heart defects are more common with trisomic segments extending through 9q22-9q32. A graphic method illustrates this progression in the partial trisomy 9 malformation spectrum as the triplicated chromosome region extends from bands 9p21 to 9q32. More severe and random defects are observed with complete trisomy 9 or tetrasomy 9p, suggesting an extreme excess of material greatly increases developmental variability.

Interstitial deletion of chromosome 3p: report of a patient and delineation of a proximal 3p deletion syndrome

We report on a patient with a de novo interstitial deletion of the proximal portion of the short arm of chromosome 3 (p12----14.2). The deleted portion excludes the constitutive fragile site assigned to band 3p14. The phenotype of the patient, together with that of three previously reported cases, seems to be sufficiently characteristic to allow the delineation of a proximal 3p deletion syndrome.

Gross anatomical studies of a newborn infant with the Meckel syndrome

A male infant with the Meckel syndrome was studied anatomically. The findings were compared to those from eight trisomy 13 cases to determine whether or not the superficial similarities between the two syndromes were matched by similarities in the internal variations. Emphasis was on the head and limbs. In the head, major differences were found in the nasal bones, mandible, and tongue. In the limbs, the skeletal variations were more severe in the Meckel syndrome infant, but he lacked the muscle variations diagnostic of trisomy 13.

Genetics, ageing and dementia

The contribution of genetic differences to variation in ageing and the relationship of ageing to certain types of dementia are discussed. Neuropathological changes commonly found in the ageing brain are present in more severe form in Alzheimer-type dementia, Down's syndrome, multi-infarct dementia, and a substantial number of patients with Parkinson's disease. An increased frequency of ageing-associated changes outside the brain have been reported in Alzheimer-type dementia, Down's syndrome, and multi-infarct dementia, although the evidence is generally meagre and in many cases requires further corroboration. Genetic studies of Alzheimer-type dementia support the existence of heterogeneity on the basis of family history and age of onset; early onset is associated with greater genetic risk and severity of abnormality. The increasing evidence of an association between DNA damage, premature ageing, and neuronal cell loss may provide insights into the aetiology of these and other forms of dementia.

Developmental pathogenesis of chromosome disorders: report on two newly recognized signs of Down syndrome

Testing the hypothesis of amplified developmental instability in autosomal trisomies as proposed by Shapiro we predicted and found an increased frequency of symphalangies in the toes of patients with Down syndrome. In our X-ray study of the feet of 71 adults with trisomy 21 we also detected a greater than normal number of sesamoid bones. A corollary to Shapiro's hypothesis is a dependence on ethnic origin of the frequency of symptoms in Down syndrome. Compared to data from Europe, toe symphalangies are more prevalent in Japan. We predict this anomaly to occur even more often in Japanese patients with trisomy 21.

Analysis of gross anatomical variations in human triploidy

Three cases of human triploidy were dissected in detail to determine whether or not there are any specific patterns of morphologic variation associated with this form of polyploidy. No specific constellations of anatomic variation were observed. However, each body did have a greater than normal number of variations among muscles that tend to be variable in the normal population. Two bodies showed a marked increase in the size of the thigh muscles, two bodies had eyeballs that were larger than normal, and two bodies had anomalous attachments of the extraocular muscles. The sample size is not large enough to draw any specific conclusions concerning the pathogenesis of these variations. However, the findings do suggest that careful examination of additional specimens will be of value in providing further information about the genotype/phenotype relationships in human triploidy.