Midline developmental anomalies in Down syndrome.

Infants with Down syndrome are known to have a high frequency of birth defects, particularly cardiac and gastrointestinal defects. Mental retardation of different degrees is common, but accompanying central nervous system malformations are rare. We report a boy born spontaneously in the 37th postconceptional week with multiple malformations: microcephaly, hypertelorism, blepharophimosis, medial cleft palate, micrognathia, omphalocele, and pathologic palmar and plantar creases. Cardial sonography revealed a ventricular septal defect and mild pulmonary stenosis. Cranial magnetic resonance imaging demonstrated a general but infratentorial stressed brain atrophy with widening of the inner and outer cerebrospinal fluid spaces and dysplasia of the corpus callosum. Chromosomal analysis showed a free trisomy 21. The boy had muscular hypotonia and developed severe motor and mental retardation, accompanied by microsomia and generalized epileptic seizures. At age 8 months, he died of sudden nocturnal respiratory and cardiac failure. The peculiarity of this case is the combination of Down syndrome with midline developmental defects (callosal dysplasia, medial cleft palate, omphalocele) accompanied by severe malformative encephalopathy. There are no previous reports of this combination, but there are genetic links between Down syndrome and midline defects concerning the Drosophila single-minded (sim) gene. The expression pattern of the human sim corresponding gene suggests that it might be involved in the pathogenesis of midline defects in Down syndrome.