[Assessment of reliable quantification of the dynamics of cerebrospinal fluid by magnetic resonance imaging in idiopathic normal pressure hydrocephalus]

INTRODUCTION

A combination of good clinical selection with reliable quantification of diverse parameters that characterize the dynamics of cerebrospinal fluid (CSF) flow from phase-contrast magnetic resonance imaging may identify patients with idiopathic normal pressure hydrocephalus (NPH).

MATERIAL AND METHODS

We have carried out a quantitative analysis of 38 subjects (19 healthy subjects and 19 patients with suspected idiopathic NPH). The images were acquired using a 1.5 T MR unit with a phase-contrast sequence in an oblique-transversal plane perpendicular to the Sylvius aqueduct codified to 20 cm/s and with 27 observations per cardiac cycle by means of retrospective synchronization. The area was defined to half the height of the peak velocity, to maximize accuracy. Parameters quantified were mean flow, maximum systolic and diastolic flow, maximum systolic and diastolic velocity, mean velocity, CSF production and stroke volume.

RESULTS

All the parameters measured showed a significant difference (ANOVA: p<or=0,05) between controls and patient except for the maximum systolic velocity (p=0.17). It was observed in the discriminant analysis that the two groups (controls and patients) were classified correctly in 92.1% with the use of the maximum systolic flow and CSF production.

CONCLUSIONS

Semiautomatic quantification of the dynamics of CSF by means of MRI differentiates patients with hyperdynamic state from the control subjects, with significant differences that can be used to classify idiopathic HNP.

Improved characterization of FSHD mutations

Facioscapulohumeral muscular dystrophy (FSHD) is caused by the shortest alleles of the 3.3kb-tandem repeat array D4Z4 at 4q35. Molecular diagnosis of FSHD depends upon the separation of unusually large alleles by pulse-field electrophoresis after EcoRI and EcoRI/BlnI digestion. The exact number of alleles could not however be directly inferred from the size of DNA fragments owing to polymorphisms in the telomeric region of the locus. Knowing the exact repeat number of disease causing alleles may benefit genetic counselling, help to understand the mechanism of this singular disease and the population dynamics of subtelomeric sequences variations. We present here a partial digestion mapping method giving the exact number of repeats for disease causing alleles, and we suggest that most inaccuracies induced by common polymorphisms could be reduced by using EcoRV in place of EcoRI. After studying more than 300 DNA samples with both the standard method and this new method, we show that alleles size can be evaluated with a precision of less than one half repeat, and that the variations in length of the truncated repeat in the telomeric region of the D4Z4 locus can be evaluated. The results suggest that at least one intact chromosome 4 type repeat at 4q35 is needed to cause FSHD.

Genetic analysis of apomixis in Citrus and Poncirus by molecular markers

Propagation of citrus rootstocks depends upon the production of clonal plants from nucellar seedlings. This makes apomixis one of the host important traits in breeding programs for citrus rootstocks. The genetic control of apomixis was studied in a 50-tree progeny derived from the cross C. volkameriana×P. trifoliata using 69 molecular markers and bulked segregant analysis. The proportion of nucellar seedlings was estimated by isoenzymatic analysis of 25 seedlings per tree for 2 consecutive years. The type of embryony (polyembryonic versus monoembryonic seeds) was also determined for fruit-yielding trees. Separate genetic maps for each parental species were developed. The integration and comparison of these maps could be accomplished using common multiallelic segregant loci. Differences in gene synteny between the two species-specific genetic maps were shown. Important distortions in the segregation of markers at several genomic regions, some of them also involving differences in the C-methylation pattern, have been observed, especially for the pollen parent. Analysis of quantitative trait loci (QTLs) revealed the presence of six genomic positions (two in P. trifoliata and four in C. volkameriana) contributing individually up to 24% of the total variation for apomixis. Within the same species, QTLs with positive and negative allele effects were present, even in the same linkage group. One of the markers associated to apomixis (Apo2) is also associated to embryony type. Therefore, the genetic control of apomictic reproduction found in citrus (nucellar embryony) is quite complex compared to what has been reported for gametophytic apomixis. Molecular markers linked to QTLs governing apomixis will be useful to assist selection of future apomictic rootstocks for citrus varieties.

A gene for non-specific X-linked mental retardation (MRX55) is located in Xp11

A new family with a non-specific X-linked mental retardation (MRX55) is described. An X-linked recessive inheritance is suggested by the segregation from two healthy transmitting females of moderate mental retardation in three males, without any specific clinical, radiological or biological features. Two point linkage analysis demonstrated significant linkage between the disorder and several markers in Xp11 (Zmax = 2.11, theta = 0); multipoint linkage analyses confirmed the significant linkage with a maximum lod score (Z = 2.11 at theta = 0, at DXS8012). Recombination events observed with the flanking markers DXS1068 and DXS1275 delineate a 34 centimorgan interval in the pericentromeric region. The interval of assignment pointed out in this family overlaps with several MRX loci previously reported in Xp11 which are reviewed here in.