An unusual presentation of trisomy 9p syndrome with a partial Dandy-Walker malformation.

Abstract

Sir: Trisomy 9p may be the fourth most common autosomal condition after trisomies 21, 18 and 13. We report a child with trisomy 9p who had a partial Dandy-Walker malformation and maldevelopment of the limbic system. We suggest that these abnormalities may be part of the syndrome but have not been described previously due to the infrequent investigation of cases with MRI. The patient was the ®rst male child of nonconsanguinous Vietnamese parents. At 3 weeks of age the infant was referred to us by a community midwife and dysmorphic features were noted. The clinical features present were typical of trisomy 9p syndrome and included midfacial hypoplasia, hypertelorism, low-set ears, micrognathia, epicanthic folds, ``cup-like'' simple ears and downturned corners of the mouth. The infant also had bilateral simian palmar creases and bilateral clinodactyly but nail dysplasia, present in the majority of cases with trisomy 9p, was not found. His karyotype was 46,XY, dup(9)(p12p24). The karyotypes of both parents were normal. At follow up, because of a large anterior fontanelle and developmental delay, brain MRI was performed. This demonstrated the presence of a partial Dandy-Walker malformation with a possible cyst in the cisterna magna (Fig. 1) and abnormal development of the limbic system (Fig. 2). This case demonstrated some of the classical features of trisomy 9p [1]. The ®ndings on the MRI scan of a partial Dandy-Walker malformation and maldevelopment of the limbic system have not been previously reported although a similar picture has been described in trisomy 9 mosaicism [2]. It is likely that previous cases with trisomy 9p would not have had the bene®t of an MRI scan. We would recommend that a brain MRI should become part of the routine investigation of all children with trisomy 9p if they are to be appropriately evaluated.