Errors of morphogenesis and inborn errors of immunity 20 years after the discovery of DiGeorge anomaly

Rubinstein-Taybi Syndrome with thymic hypoplasia

We report the autopsy findings in a 20-month-old boy with Rubinstein-Taybi syndrome and DiGeorge sequence. No visible thymus was demonstrated at the time of autopsy. With careful microscopic examination, a few pieces of thymic tissues found near the thyroid gland showed remarkable depletion of both thymocytes and cortical epithelial cells. Immunohistological staining with T-cell surface antigens resulted in a definite positive reaction. Repeated respiratory infections present in this patient may, in part, be attributable to thymic hypoplasia. Other major anomalies included broad thumbs and great toes, microphthalmia, arrhinencephaly, patent ductus arteriosus, stenosis of the ureterovesicular junction, bilateral cryptorchidism, and minor facial anomalies.

DiGeorge anomaly associated with 10p deletion

DiGeorge anomaly (DGA) represents a heterogeneous entity, which is often sporadic, although familial cases and the association with monosomy 22q11 have been reported. Recently, a few patients with 10p deletion syndrome and immunological and other laboratory findings similar to DGA have been described. We report on an additional case of partial DGA associated with 10p deletion.

The DiGeorge sequence. II. Immunologic findings in partial and complete forms of the disorder

We present immunological in vitro data on a group of 16 patients with the DiGeorge sequence (DGS). Detailed tests gave evidence that the decrease in number and function of mature T-cells is closely correlated with phenotypic expression and represents a wide immunological spectrum ranging from normal function to severe combined immunodeficiency with B-cells. Careful immunological testing in DGS may help to plan therapeutic procedures (i.e. thymic factor therapy or bone marrow transplantation), may also have prognostic significance and help to gain insight into mechanisms operative in disturbances of T-cell regulation.

The DiGeorge syndrome. I. Clinical evaluation and course of partial and complete forms of the syndrome

This study describes clinical signs and symptoms in 16 patients with the DiGeorge syndrome (DGS). Diagnosed on the basis of typical facial stigmata, a broad spectrum of severity is seen with respect to congenital heart disease, hypoparathyroidism and immunologic parameters. A simple index of severity is introduced that clearly differentiates complete forms of the syndrome (cDGS) with poor prognosis from partial forms of the syndrome (pDGS). Of 13 pDGS patients, 12 are still living; 8 underwent corrective heart surgery without infectious complications. Moderate to severe mental retardation is seen in all pDGS patients. Due to the lack of thymus function, immunodeficiency is a result of cDGS, whereas immunoregulatory disturbances (hypergammaglobulinaemia, high titres of specific antibody production) prevail in pDGS patients.

Human chromosome 22

The acrocentric chromosome 22, one of the shortest human chromosomes, carries about 52 000 kb of DNA. The short arm is made up essentially of heterochromatin and, as in other acrocentric chromosomes, it contains ribosomal RNA genes. Ten identified genes have been assigned to the long arm, of which four have already been cloned and documented (the cluster of lambda immunoglobulin genes, myoglobin, the proto-oncogene c-sis, bcr). In addition, about 10 anonymous DNA segments have been cloned from chromosome 22 specific DNA libraries. About a dozen diseases, including at least four different malignancies, are related to an inherited or acquired pathology of chromosome 22. They have been characterised at the phenotypic or chromosome level or both. In chronic myelogenous leukaemia, with the Ph1 chromosome, and Burkitt's lymphoma, with the t(8;22) variant translocation, the molecular pathology is being studied at the DNA level, bridging for the first time the gap between cytogenetics and molecular genetics.

Embryologic and other developmental considerations of thirty-eight possible variants of the DiGeorge anomaly

The DiGeorge anomaly (DGA) represents a polytopic developmental field defect that can be caused by a number of different chromosomal, mendelian, toxic, or metabolic factors operating in early embryonic life. If the affected field is thought to be focused on either the fourth branchial arch or the third branchial pouch, with variable cephalad or caudad extension, 38 different combinations of malformations can include DiGeorge anomalies, 24 complete and 14 partial DGA, with the constraints that the field defect must be contiguous (involvement of more than one branchial arch or pouch requires involvement of all intervening arches or pouches) and complete (all derivatives of an affected branchial arch or pouch are deficient). The types and relative frequencies of abnormalities of structures other than the thymus and parathyroid glands in these possible "subsets" of DGA are discussed, and the need for more data on their occurrence in patients diagnosed as having DGA is emphasized.

"Inborn errors of metabolism" and "chemical individuality", two ideas of Sir Archibald Garrod briefly revisited 50 years after his death

Two ideas of Sir A. Garrod, "chemical individuality" (1902) and "inborn errors of metabolism" (1908) have proved fundamental for the development of medical knowledge. The latter idea was more fortunate than the former which, however has been extremely heuristic. On the other hand the two ideas are not entirely independent of each other: in fact, a third Garrodian concept, "inborn factors in disease", represents a significant link between them. "Inborn errors of metabolism" revived the laws of genetics and opened the way to interpretation of the molecular diseases with all their inherent practical modern implications (neonatal screening, prenatal diagnosis, and in perspective, genetic engineering). "Chemical individuality" still constitutes a valid premise for knowledge of biological individuality (in other words, the "biological ego") fundamentally programmed for conservation of self and for continuous discrimination of self versus non-self.

The DiGeorge anomaly as a developmental field defect

The DiGeorge "syndrome" is a characteristic malformation pattern involving craniofacial, cardiac, thymic, and parathyroid structures. Evidence is accumulating that the DiGeorge "syndrome" is actually not a syndrome, but a polytopic developmental field defect. We present evidence of causal heterogeneity of the DiGeorge anomaly. This heterogeneity will be discussed in the light of recent findings that indicate that the dysmorphogenetically reactive unit responsible for the phenotype of the DiGeorge anomaly is a population of cephalic neural crest cells.