[Ocular coloboma and results of brain MRI: preliminary results]

INTRODUCTION

Congenital ocular colobomas are the result of a failure in closure of the embryonal fissure. We present a prospective study (2007-2011) in which we report brain MRI findings in children with ocular coloboma.

PATIENTS AND METHODS

Thirty-five children (54 eyes) were included; 15 boys, 20 girls with a median age of 24.0 months (1.0-96.0) at first presentation. Within 2 to 3 months following complete ophthalmologic examination, brain MRI was performed.

RESULTS

Colobomas were bilateral in 19 cases and unilateral in 16 cases. Eleven different types of coloboma were identified. Of 54 eyes, 74% demonstrated optic nerve coloboma, of which 28 were severe. Of 35 MRI's performed, abnormalities were present in 86%: gyration abnormalities (n=21), lateral ventricular dilatation (n=17), dilatation of the Virchow-Robin and subarachnoid spaces (n=14), signal abnormalities and brain stem malformations (n=14), white matter signal abnormalities (n=11), corpus callosum abnormalities (n=10). Most of these abnormalities were related. Gyration abnormalities were the most frequent. There was no significant association between the severity of the coloboma and the abnormalities found (P=1.0). Likewise, there was no significant association of gyration abnormalities with the severity of coloboma in children (P=1.0).

DISCUSSION AND CONCLUSION

This study shows, for the first time, the existence of frequent cerebral abnormalities on MRI in children with ocular coloboma. The most common abnormality being gyration abnormalities, in 60% of cases.

Molecular background of D-negative phenotype in the Tunisian population

BACKGROUND

Most studies of the molecular basis of Rhesus D-negative phenotype have been conducted in Caucasian and African populations. A comprehensive survey of RHD alleles was lacking in people from North Africa (Tunisians, Moroccans and Algerians) which could be very efficient for managing donors and patients carrying an RHD molecular variant. We analyse the molecular background of D-negative population in Tunisia in the present study.

MATERIALS AND METHODS

Blood samples were collected from native Tunisians. A total of 448 D-negative donors from different regions of Tunisia were analysed by RHD genotyping according to an adopted strategy using real-time PCR, ASP-PCR and sequencing.

RESULTS

Among the 448 D-negative samples, 443 were phenotyped unequivocally as true D-negative including three molecular backgrounds which were RHD gene deletion (n = 437), RHDψ pseudogene (n = 2) and RHD-CE-D hybrid gene (n = 4) with the respective frequencies of 0·9900, 0·0023 and 0·0046. The remaining five samples, in discordance with the serological results, were identified as two weak D type 11, one weak D type 29, one weak D type 4·0 and one DBT-1 partial D.

CONCLUSION

This study showed that the Tunisian population gets closer to Caucasians, given that the RHD gene deletion is the most prevalent cause of D-negative phenotype, but it is slightly different by the presence of the RHDψ pseudogene which was found with a very low frequency compared with that described in the African population. Nevertheless, the relative occurrence of weak D variants among studied serologically D-negative samples make necessary the adaptation of RHD genotyping strategy to the spectrum of prevalent alleles.

Total and fetal cell-free DNA analysis in maternal blood as markers of placental insufficiency in intrauterine growth restriction

OBJECTIVE

To compare total and fetal DNA levels in the maternal plasma in three groups: pregnancies with intrauterine growth restriction (IUGR) due to placental insufficiency (PI) and other causes, and in control pregnancies.

METHODS

Total as well as fetal DNA was quantified in 78 maternal plasma samples. In 19 pregnancies, the fetus presented IUGR due to PI (group A), and in 31 pregnancies due to other causes (group B). The control group comprised 28 patients (group C). DNA quantification was done using real-time quantitative PCR with a standardized pool of plasmid calibrators. DNA concentrations of the three groups were compared using non-parametric tests (Kruskal-Wallis or Mann-Whitney tests).

RESULTS

The three groups did not statistically differ regarding maternal age (mean +/- SD: 30.5 +/- 5.4 years), gestational age (30 +/- 5.3 weeks) or the proportion of male fetuses (48.2%). Plasma total DNA was significantly higher in group A compared to groups B and C (p = 0.001 for both). An increase in fetal DNA was only observed in group A for patients beyond 28 weeks of gestation.

CONCLUSIONS

The plasma total DNA level is higher in patients with IUGR due to PI. These results suggest the presence of maternal endothelial damage independently of preeclampsia.

Expression of the mRNA for the beta 2 subunit of the voltage-dependent sodium channel in rat CNS

Expression of the voltage-dependent sodium channel has been analysed in adult rat central nervous system by Northern blotting and in situ hybridization. Northern blots showed that all the territories studied express beta 2 transcripts, albeit with widely varying levels (with cerebellum >> hippocampus > brain > brainstem > spinal cord). In situ hybridization confirmed that in these structures, all the neuronal cell bodies contain beta 2 mRNA; expression was particularly high in the granule cells of the cerebellum, in both pyramidal cell layer and dentate gyrus in the hippocampus, and in spinal cord motor neurons. Northern blots also showed that RNA extracted from optic nerve and cultured cortical astrocytes contained beta 2 mRNA, while it was totally absent from sciatic nerve. In situ hybridization evidenced the presence of a numerous population of beta 2-positive cells in cerebellum white matter, spinal cord white matter, and in corpus callosum, where frontal sections showed labelled cells arranged in the chain-like or row pattern typical of interfascicular oligodendrocytes. Combination of antiglial fibrillary acid protein (GFAP) immunofluorescent histochemistry with detection of beta 2 mRNA evidenced that expression of the transcripts was indeed restricted to GFAP-negative cells in white matter.

Prenatal diagnosis of 22q11 microdeletion

Microdeletion of 22q11 is responsible for DiGeorge syndrome, velocardiofacial syndrome, congenital conotruncal heart defects, and related disorders. Familial transmission accounts for about 10-20 per cent of cases and most of the parents with deletions are nearly asymptomatic. This phenotypic variability makes it difficult to give appropriate genetic counselling. We report our experience on prenatal diagnosis of 22q11 deletion. We proposed prenatal detection of 22q11 microdeletion in 33 pregnancies. In two instances the parents refused prenatal diagnosis and one pregnancy ended spontaneously before the time of sampling. Fluorescent in situ hybridization (FISH) analysis on cultured amniotic cells with probes mapping in the commonly deleted region was used in the remaining 30 cases. Indications were classified into two groups. The first group included four couples with an abnormal family history of a deleted child and/or a deleted parent. No deletion was found in this group. The second one concerned pregnancies with a prenatally detected heart defect. Among these pregnancies with abnormal ultrasound findings, three deletions were found in the 26 samples tested.

i(18q) in amniotic and fetal cells with a normal karyotype in direct chorionic villus sampling: cytogenetics and pathology

A case of false-negative discrepancy between results of chorionic villi (direct preparation) and those of fetal tissue with an isochromosome 18q [i(18q)] in amniotic cells and fetal blood is reported. Fluorescence in situ hybridization (FISH) confirmed this uncommon chromosomal rearrangement. The fetus showed cyclopia and multiple congenital anomalies which have never been reported in cases of i(18q).

[Microdeletion of the chromosome 22q11 in children: apropos of a series of 49 patients]

Most of the children with Di George syndrome and 60% of patients with velocardiofacial syndrome exhibit a microdeletion within chromosome 22q11. The phenotypic expression of this chromosomal abnormality is highly variable.

PATIENTS

Forty-nine children, 0 to 15 years of age, were demonstrated as carriers of a 22q11 microdeletion. The main referral diagnoses were: Di George syndrome (19 cases), velocardiofacial syndrome (14 cases); congenital heart defect with dysmorphism (9 cases); hypoparathyroidism (2 cases). The microdeletion was detected by fluorescent in situ hybridization with probes specific of the 22q11 region.

RESULTS

Facial dysmorphism was the only constant feature. A congenital heart defect was present in 84% of cases. Significant hypocalcemia was documented in 51% of cases and thymic hypo or agenesis in 83%. Significant immune deficiency was documented in nine cases. The most frequent associated defects were urinary tract malformations (8 cases). A cleft palate was present in height enfants but velopharyngeal insufficiency was almost constant. Two-thirds of children had psychomotor delay, and five children exhibited behavioral problems. Of the 35 couples of parents tested, eight mothers were found to be carriers of the deletion.

CONCLUSION

For the pediatrician, it is essential to know the variability of the clinical picture. The long-term prognosis is conditioned by the possibility of mental retardation and learning disabilities. Parents should be tested for the presence of the deletion. The occurrence of the microdeletion in asymptomatic relatives raises difficult problems in genetic counselling.

Clinical and molecular study of DiGeorge sequence

DiGeorge sequence (DGS) is a developmental field defect of the third and fourth pharyngeal pouches. The cardinal features of the syndrome are hypo- or aplasia of the thymus and parathyroids, congenital heart defect of the conotruncal type and characteristic facial dysmorphism. Such a pattern of malformations has been associated with various conditions but it is now well established that most cases of DGS are due to haplo-insufficiency of the chromosome 22q11 region. We report here a series of 16 patients, including a familial case. Minimal criteria for inclusion in this series were two or more of the following features: conotruncal heart defect, hypocalcaemia, hypoplastic/absent thymus and typical facial dysmorphism. Molecular analysis with specific probes of the 22q11 region was conducted in all patients according to two methods, fluorescent in situ hybridization and DNA dosage analysis. A deletion was found at the molecular level in all patients. We emphasize the fact that clinical analysis remains an important step of the diagnosis. The implication of these molecular techniques on diagnosis, prognosis and genetic counselling of DGS are discussed.