Anatomical analysis of the developmental effects of aneuploidy in man—the 18‐trisomy syndrome: I. Anomalies of the head and neck

Abstract

This paper describes the anatomical variations observed in the head and neck in eight infants with the 18-trisomy syndrome that were dissected and studied in detail. Of the usual muscles of facial expression, occipitofrontalis and the auricular and nasal muscles were hypolastic in all eight bodies and each subject showed extensive fusion of the muscles around the corner of the mouth. In each body there was a supernumerary muscle band that extended from the region near the corner of the mouth to the occipital attachment of trapezius. The otomandibular region in each body showed a variable spectrum of muscular, skeletal, arterial, and salivary gland variations bilaterally. Three of the bodies had infrahyoid muscle variations. The sum of these observations provides a more complete delineation of the variations that occur in the 18-trisomy syndrome. Tentative pathogenetic hypotheses for several of the defects are discussed, based on observations from human descriptive embryology. Poswillo's teratological model [1973] implicating hemorrhaging as a causal mechanism in human first and second branchial arch malformations is suggested as a possible mechanism to explain the bilateral otomandibular defects.

Strawberry-Shaped Skull in Fetal Trisomy 18

“…Similarly, flattening of the occiput may be due to hypo plasia of the hindbrain. Thus, postnatal and post-mortem studies have documented hypo plasia of the frontal lobes and poor develop ment of the facial artery, several of the facial muscles, of the maxilla, mandible, frontal as well as the temporal bones, together with mi crophthalmia, narrow nasal bridge and palate, and absent or rudimentary parotid and sub mandibular salivary glands [4][5][6], These fea tures may be the consequence of abnormal development of the first and second branchial arches, due to vascular defects [7], Hindbrain abnormalities include hypoplasia of the oc cipital lobes, cerebellum and brain stem, and the alteration in the shape of the occipital bones may be due to abnormalities of in duction of the skull by the developing brain [4,8,9], In the trisomic fetuses without a strawber ry-shaped skull, the higher incidence of poste rior fossa cysts may have prevented the flat tening of the occipital bones, and the lower incidence of micrognathia may be indicative of lesser degrees of facial hypoplasia and therefore lesser pointing of the frontal bones.…”

Multiple congenital anomaly/mental retardation (MCA/MR) syndrome with Goldenhar complex due to a terminal del(22q)

“…The phenotype has also been seen in infants with trisomy 18 [Bersu and Ramirez-Castro, 1977;Greenberg et al, 19883, dup(7q) [Hoo et al, 19821, and ring chromosome 21 [Greenberg et al, 19881. Finally, a patient with Klinefelter syndrome [Poonawalla et al, 19801 and 49,XXXXY syndrome [Kushnick and Colondrillo, 19751, respectively, have had hemifacial microsomia.…”

Chromosomal abnormalities associated with congenital contractures (arthrogryposis)

“…Absence of the olfactory bulbs, hypoplastic frontal lobes, rudimentary corpus callosum, absence of septum pellucidum, and absence of the ciliary ganglia have been described in trisomy 13 (Aziz 1980, Petterson et al 1978. Defects in the falx cerebri, absence or hypoplasia of the corpus callosum and hypoplasia of the cerebellum and brainstem have been observed in trisomy 18 (Bersu & Ramirez-Castro 1977, Barash et al 1970. Patient 3 (trisomy 8) had hypoplasia of the anterior commissure, sep-tum pellucidum and fornix.…”