Trisomy 17 mosaicism is one of the rarest autosomal trisomies in humans. Thus far, only 23 cases have been described, most of them detected prenatally. In only five instances has mosaicism been demonstrated in lymphocytes and/or fibroblasts postnatally, and only in these have multiple congenital anomalies (MCA), facial dysmorphisms, and mental retardation been reported. Patients with trisomy 17 mosaicism at amniocentesis and a normal karyotype in blood and fibroblasts (n = 17) were always healthy. Here, we report on pre- and postnatal clinical, cytogenetic, molecular-cytogenetic, and molecular findings in four patients with trisomy 17 mosaicism. The first case was detected in cultured but not in short-term chorionic villi and amniocytes. Due to MCA on prenatal ultrasound examination the pregnancy was terminated. The second patient is a 13-month-old healthy boy, in whom low level trisomy 17 mosaicism was detected in cultured chorionic villi only. The third patient is a 2-year-old girl with growth retardation, developmental delay, MCA, and trisomy 17 mosaicism in amniocytes, fibroblasts, and placenta, but not in blood and buccal smear. The fourth patient is a 9-year-old boy with growth and mental retardation, sensoneurinal hearing loss, and MCA. Cytogenetic analyses showed trisomy 17 mosaicism in amniocytes, skin fibroblasts, and urinary sediment cells, whereas in blood and buccal smear a 46,XY karyotype was found. Molecular investigations in all four cases indicated biparental inheritance of chromosome 17. Formation of trisomy was most likely due to a maternal meiosis I error in Patient 1 and a postzygotic non-disjunction of the paternal chromosome 17 in Patient 4. Cerebellar malformations, reported in two cases from the literature and in two reported here may be a specific feature of trisomy 17 mosaicism. Since the aberration has rarely been reported in lymphocytes, chordocentesis is not indicated in prenatal diagnosis. Prenatal genetic counseling for trisomy 17 mosaicism in chorionic villi or amniocytes should consider that the clinical significance remains uncertain.
The oxaloacetate decarboxylase (OAD) Na + pump consists of subunits a, b, and c, which are expressed from an oadGAB gene cluster present in various anaerobic bacteria. Vibrio cholerae has two copies of oad genes, which are termed oad-1 and oad-2. The oad-2 genes are part of the citrate fermentation operon, while the oad-1 genes are flanked by genes encoding products not involved in a catabolic pathway. The gene sequences of oad-1 and oad-2 of V. cholerae strain O395-N1 were determined. The apparent frameshift in the published sequence of the oadA-2 gene from V. cholerae El Tor N16961 was not present in strain O395-N1. Upon anaerobic growth of V. cholerae on citrate, exclusively the oad-2 genes are expressed. OAD was isolated from these cells by monomeric avidin-Sepharose affinity chromatography. The enzyme was of higher specific activity than that from Klebsiella pneumoniae and was significantly more stable. Decarboxylase activity was Na + dependent, and the activation profile showed strong cooperativity with a Hill coefficient n H =1.8. Oxalate and oxomalonate inhibited the enzyme with half-maximal concentrations of 10 lM and 200 lM, respectively. After reconstitution into proteoliposomes, the enzyme acted as a Na + pump. With size-exclusion chromatography, the enzyme eluted in a symmetrical peak at a retention volume corresponding to an apparent molecular mass of approximately 570 kDa, suggesting a tetrameric structure for OAD-2. The two oad gene clusters were heterologously expressed in Escherichia coli, and the decarboxylases were isolated from the host cells.
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