Karsten R. Held

Mosaicism in 45,X Turner syndrome: does survival in early pregnancy depend on the presence of two sex chromosomes?

SummaryCytogenetic and molecular genetic findings in 91 patients with Turner syndrome are reported. In 87 patients, chromosome studies were carried out both in lymphocyte and fibroblast cultures. Mosaicism was demonstrated in 58 of these patients (66.7%), whereas only 18 (20.7%) were apparent non-mosaic 45,X, and 11 patients (12.6%) showed non-mosaic structural aberrations of the X chromosome. Among the mosaic cases 16 (18.4% of all patients) displayed a second cell line containing small marker chromosomes. The association of Y-specific chromosomal material with the presence of marker chromosomes was demonstrated in 6 out of 7 mixoploid fibroblast cell lines by polymerase chain reaction amplification and by Southern-blot analysis. The observation of ring formation and morphological variability in vivo and in vitro, and the continous reduction in the percentage of cells containing marker chromosomes in longterm cultivation experiments indicated an increased instability of marker chromosomes. The findings suggest that in vivo selection of structurally altered sex chromosomes exists. Thus, the observation of apparent non-mosaic 45,X chromosomal complements in liveborn individuals with Turner syndrome does not contradict the hypothesis that some degree of mosaicism is necessary for survival in early pregnancy.

Expression of RPS4X in fibroblasts from patients with structural aberrations of the X chromosome.

SummaryA series of fibroblasts from patients with numerical or structural aberrations of the X chromosome were scored for the amount of mRNA of ribosomal protein S4 (RPS4X). Haplo-insufficiency of this gene has been reported previously to be a possible cause of Turner syndrome. Our results show that the transcription rate of RPS4X correlates with the number of gene copies. This confirms earlier findings indicating that this gene escapes X inactivation. In addition, we demonstrate that this applies to structurally aberrant X chromosomes. Our results show that RPS4X does not give rise to a type of haplo-insufficiency in these cases, because it escapes inactivation, even on structurally aberrant X chromosomes from patients with Turner syndrome. We therefore assume that RPS4X is not the most prominent candidate gene for Turner syndrome.

A case of lipogranulomatosis Farber: some clinical and ultrastructural aspects.

A 20-month-old girl showed typical clinical signs of Farber disease: hoarseness since birth, and periarticular subcutaneous painful nodules. Complete deficiency of acid ceramidase activity was found in cultured skin fibroblasts. An electron microscopic examination of a dermal nodule disclosed pathognomonic tubular inclusions in histiocytes. In epidermal cells zebra-body-like and needle-like lysosomal inclusions were found. Their ultrastructure is different from that of the intrahistiocytic lysosomal inclusions.Probably three clinical types of Farber disease may be distinguished according to the symptomatology and the course of the discase: a severe type, an intermediate type and a relatively mild type. The activity of acid ceramidase does not correlate with prognosis of the disease, while a correlation between first appearance of dermal nodules and clinical course appears likely.

Ullrich-Turner syndrome is not caused by haploinsufficiency of RPS4X

Ullrich-Turner syndrome (UTS) is frequently associated with monosomy X but may also occur with structural aberrations of the X and the Y chromosomes. It has been hypothesized that the ribosomal protein genes RPS4X and RPS4Y play a critical role in the prevention of UTS. Individual patients with a 46,X,i(Xq) karyotype cannot be differentiated phenotypically from 45,X UTS patients and carry three gene copies of RPS4X. Since haploinsufficiency of one or several gene(s) is thought to cause the UTS phenotype, direct assessment of RPS4X expression levels in these patients should establish whether RPS4X is involved in UTS. We have investigated fibroblasts of four 46,X,i(Xq) UTS patients with typical symptoms and a non-mosaic chromosome complement, and have found significantly increased RPS4X mRNA levels in all patients. Based on our results, we conclude that haploinsufficiency of RPS4X is not the cause of UTS.

New biochemical and immunological data on quantitative and qualitative variability of human pseudocholinesterase

Summary1.The comparison of the tryptic peptides of usual and dibucain-resistent Pseudocholinesterase revealed a different electrophoretic mobility of those peptides which can be labelled with radioactive DFP. The results suggested the loss of a negative charge near the esteratic site of the active center in the variant enzyme.2.The investigation of quantitative interindividual variation of Pseudocholinesterase antigen and enzyme activity in a sample of the population showed a high correlation of the values. Sera containing the C5-variant have more antigen than C5-negative sera. A possibility to detect subtoxic exposure to organophosphates was pointed out.3.Immunological and biochemical investigations on human cultured fibroblasts from normal and enzyme deficient individuals failed to give evidence for the synthesis of Pseudocholinesterase.Zusammenfassung1.Der Vergleich der tryptischen Peptide von normaler und dibucain-resistenter Pseudocholinesterase zeigte eine unterschiedliche elektrophoretische Beweglichkeit für die mit radioaktivem DFP markierbaren Peptide. Die Ergebnisse ließen auf den Verlust einer negativen Ladung in der Nähe der esteratischen Stelle des aktiven Zentrums bei der Enzymvariante schließen.2.Die quantitative Untersuchung der interindividuellen Variabilität des Pseudocholinesteraseantigens und der Enzymaktivität in einer Stichprobe der Bevölkerung ergab eine enge Korrelation der Werte. Seren, die die C5-Variante enthielten, hatten mehr Pseudocholinesteraseantigen als C5-negative Seren. Die Möglichkeit der Erkennung subtoxischer Insecticidbelastungen wurde aufgezeigt.3.Immunologische und biochemische Untersuchungen an kultivierten menschlichen Fibroblasten von normalen und enzymdefizienten Individuen ergaben keine Evidenz für die Synthese von Pseudocholinesterase.

Mesomelic dysplasia with short ulna, long fibula, brachymetacarpy, and micrognathia: Clinical and radiological differential diagnostic features

A girl with a “new” variant of mesomelic dysplasia is reported. The disorder is characterized by mesomelic brachymely, especially of the arms, a short ulna, relatively long fibula, brachymetacarpy, minor symmetrical changes at the hands, developmental arrest of the spine, contractures, and micrognathia. The clinical and radiological differential diagnostic features are discussed.

Unilateral Skin Lesions, Cataracts, Optic Glioma and Retardation – a Variant of the Epidermal Nevus Syndrome?

A girl with unilateral partly depigmented partly hyperpigmented atrophic skin lesions, cataracts, optic glioma, and mental retardation is presented. Differential-diagnostic aspects are discussed. It remains to be seen whether this case represents a variant of the epidermal nevus syndrome, an unusual type of X-linked dominant chondrodysplasia punctata or a separate nosological entity.

Gamma-glutamyl transferase activity in the amniotic fluid of fetuses with chromosomal aberrations and inborn errors of metabolism

The activity of gamma‐glutamyl transferase (GGT) was measured in amniotic fluid collected between the 16th and 30th weeks of gestation from 81 pregnancies with fetuses affected by chromosomal aberrations, nine with different types of inborn errors of metabolism, two with hemophilia A and one with fragile X syndrome. The GGT activity was compared with that from 1000 normal pregnancies and deliveries resulting in healthy newborns. Contamination of amniotic fluid by blood did not affect the GGT activity. Pathologically decreased activity was found in 25 of 56 amniotic samples from pregnancies with fetal autosomal chromosomal aberrations (44.6%). It was decreased in 15 of 35 pregnancies with fetal trisomy 21 (43%), in 11 of 19 pregnancies with fetal trisomy 18 (58%), in one of three pregnancies with fetal trisomy 13 and in two pregnancies with fetal trisomy 8 and triploidy, respectively. In only three of 16 pregnancies with fetal sex chromosomal aberrations was the GGT activity low. Increased GGT activity was found in three of six pregnancies with unbalanced structurally rearranged karyotypes of the fetuses. Normal GGT activity was observed in all nine amniotic fluid samples from pregnancies with fetuses affected with different forms of inborn errors of metabolism diseases, in the two pregnancies with hemophilia A and in the pregnancy with a male fetus with fragile X syndrome. These and earlier findings indicate that the GGT activity in amniotic fluid is mostly decreased in pregnancies with severe fetal developmental abnormalities, such as autosomal chromosomal aberrations, which could possibly be secondary to an alteration of the microvillar transport system of GGT to the amniotic fluid. GGT testing could thus be a valuable screening method for routine use in prenatal diagnosis of second‐trimester pregnancy.

Lesch-Nyhan Syndrome and HPRT Variants: Study of Heterogeneity at the Gene Level

The purine salvage enzyme hypoxanthine-guanine phospho-ribosyltransferase (HPRT: EC 2.4.2.8) catalyses the conversion hypoxanthine and guanine to their respective nucleotides, IMP and GMP. A partial deficiency of HPRT is associated with overproduction of uric acid which results in the development of severe form of Gout and nephrolithiasis.(Kelly et al. 1967). An almost complete deficiency of HPRT leads to an Xlinked disorder Lesch-Nyhan Syndrome, which in its classical form shows clinical symptoms of hyperuricemia, choreoathetosis, mental retardation and compulsive self mutilation. A large number of patients with different severity of these symptoms and levels of rest activity of HPRT have been reported and attempts have been made to classify them into various catagories on the basis of enzyme kinetics or behaviour of the cultured fibroblasts or lyphoblasts in various selection media (Page et al.1983., Singh et al., 1986). By sequence analysis of tryptic peptides, several HPRT variants have been chracterised to be due to single amino acid substitution(Wilson et al. 1983). Two of these have been recently shown to be due to point mutation of a single base by employing the strategy of cDNA cloning or genomic amplification of a specific region of the gene and followed by nucleotide sequencing (Fujimori et al., 1988; Cariello et al., 1988). Some of them have also been detected as gross rearrangements of the Gene (Yang et al., 1984.; Wilson et al. 1986). By employing the ribonuclease cleavage anlysis technique, also known as RNA mapping, Gibbs and Casky (1987) have been successful in localising a number of mutations of one to five nucleotides in five patients.

Genetic heterogeneity of hypoxanthine-phosphoribosyl transferase in human fibroblasts of 3 families.

Incorporation of hypoxanthine, resistance to 8‐azaguanine and activation by lyophilisation have been studied in cultured human fibroblasts. Cells from one family where there was a boy with Lesch‐Nyhan syndrome, from two families with variant H‐PRT mutations and three cell strains from patients with the Lesch‐Nyhan syndrome were investigated. Cells from patients with the Lesch‐Nyhan syndrome showed almost no hypoxanthine incorporation and resistance to concentrations of 8‐azaguanine up to 10‐3 M, whereas cells of patients with partial H‐PRT deficiency demonstrated variant patterns of hypoxanthine uptake and partial resistance to 8‐azaguanine. Lyophilisation of fibroblast sediment from patients with the Lesch‐Nyhan syndrome and patients with variant H‐PRT mutations showed activation of the deficient or partially deficient H‐PRT enzyme. No such activation was observed in healthy controls. Activation of lyophilised fibroblast extract from patients and controls was not obtained. These results suggest that H‐PRT could be associated with the cell membranes.