Noradrenergic neuronal development is impaired by mutation of the proneural HASH-1 gene in congenital central hypoventilation syndrome (Ondine's curse)

Congenital central hypoventilation syndrome (CCHS, Ondine's curse) is a rare disorder of the chemical control of breathing. It is frequently associated with a broad spectrum of dysautonomic symptoms, suggesting the involvement of genes widely expressed in the autonomic nervous system. In particular, the HASH-1-PHOX2A-PHOX2B developmental cascade was proposed as a candidate pathway because it controls the development of neurons with a definitive or transient noradrenergic phenotype, upstream from the RET receptor tyrosine kinase and tyrosine hydroxylase. We recently showed that PHOX2B is the major CCHS locus, whose mutation accounts for 60% of cases. We also studied the proneural HASH-1 gene and identified a heterozygous nucleotide substitution in three CCHS patients. To analyze the functional consequences of HASH-1 mutations, we developed an in vitro model of noradrenergic differentiation in neuronal progenitors derived from the mouse vagal neural crest, reproducing in vitro the HASH-PHOX-RET pathway. All HASH-1 mutant alleles impaired noradrenergic neuronal development, when overexpressed from adenoviral constructs. Thus, HASH-1 mutations may contribute to the CCHS phenotype in rare cases, consistent with the view that the abnormal chemical control of breathing observed in CCHS patients is due to the impairment of noradrenergic neurons during early steps of brainstem development.

PMX2B, a new candidate gene for Hirschsprung's disease

Hirschsprung's (HSCR) disease is a congenital intestinal malformation of the enteric nervous system. It is a multigenic malformation and until now, eight genes have been involved in the etiology of this disease: genes encoding proteins of the RET signaling pathway (RET, GDNF and NTN), genes participating in the endothelin (EDN) type B receptor pathway (EDNRB, EDN3 and ECE-1), the SOX10 gene and the SIP1 gene that is mutated in syndromic forms of HSCR. Mutations of these genes are found in not more than 50-60% of affected individuals. Here, we report on the results of a molecular cytogenetic study performed in a girl who presented with a syndromic short segment HSCR associated with a de novo t(4;8)(p13;p22) translocation. A comparative genomic hybridization (CGH) study found a 4p12p13 deletion. A molecular characterization of this rearrangement showed that the 4p13 deletion was 5 Mb in length and included the paired mesoderm homeobox gene (PMX2B) (MIM 603851), a gene expressed in the human embryonic gut and essential for the development of autonomic neural crest derivatives. The present observation suggests that PMX2B haploinsuffciency might predispose to HSCR.

Spectrum of NSD1 mutations in Sotos and Weaver syndromes

Sotos syndrome is an overgrowth syndrome characterised by pre- and postnatal overgrowth, macrocephaly, advanced bone age, and typical facial features. Weaver syndrome is a closely related condition characterised by a distinctive craniofacial appearance, advanced carpal maturation, widened distal long bones, and camptodactyly. Haploinsufficiency of the NSD1 gene has recently been reported as the major cause of Sotos syndrome while point mutations accounted for a minority of cases. We looked for NSD1 deletions or mutations in 39 patients with childhood overgrowth. The series included typical Sotos patients (23/39), Sotos-like patients (lacking one major criteria, 10/39), and Weaver patients (6/39). We identified NSD1 deletions (6/33) and intragenic mutations (16/33) in Sotos syndrome patients. We also identified NSD1 intragenic mutations in 3/6 Weaver patients. We conclude therefore that NSD1 mutations account for most cases of Sotos syndrome and a significant number of Weaver syndrome cases in our series. Interestingly, mental retardation was consistently more severe in patients with NSD1 deletions. Macrocephaly and facial gestalt but not overgrowth and advanced bone age were consistently observed in Sotos syndrome patients. We suggest therefore considering macrocephaly and facial gestalt as mandatory criteria for the diagnosis of Sotos syndrome and overgrowth and advanced bone age as minor criteria.

Febrile neutropenia and Fusobacterium bacteremia: clinical experience with 13 cases

OBJECTIVES

To assess the disease spectrum of Fusobacterium bacteremia in our neutropenic patients and review the literature.

METHODS

This was a 6.5-year retrospective study in which all the records of neutropenic patients with Fusobacterium bacteremia were analyzed.

RESULTS

Fusobacterium bacteremia was found in 13 neutropenic patients, 10 with hematological malignancies and 3 with solid tumors. The standard clinical presentation was that of primary bacteremia with benign evolution under antibiotics with anaerobic coverage. Most patients presented with oral mucositis as the probable portal of entry. Coinfection with other germs was documented in four patients. No patient had a localized infection documented. Most patients were receiving ciprofloxacin chemoprophylaxis. None of the patients had catheter-related infection. All tested strains were susceptible to all standard anaerobic agents. Fusobacterium spp. were responsible for 5% of bacteremias in neutropenic patients in our hospital during the last 6.5 years.

CONCLUSION

Fusobacterium bacteremia is a possible cause of febrile neutropenia, especially in the setting of quinolone prophylaxis and oral mucositis after intense chemotherapeutic regimens. We think that its benign outcome if there is no localized infection detected does not justify the use of antianaerobic prophylaxis. Combination of beta-lactams and beta-lactamase inhibitors is a safe and reasonable treatment.

Polyalanine expansion and frameshift mutations of the paired-like homeobox gene PHOX2B in congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS or Ondine's curse; OMIM 209880) is a life-threatening disorder involving an impaired ventilatory response to hypercarbia and hypoxemia. This core phenotype is associated with lower-penetrance anomalies of the autonomic nervous system (ANS) including Hirschsprung disease and tumors of neural-crest derivatives such as ganglioneuromas and neuroblastomas. In mice, the development of ANS reflex circuits is dependent on the paired-like homeobox gene Phox2b. Thus, we regarded its human ortholog, PHOX2B, as a candidate gene in CCHS. We found heterozygous de novo mutations in PHOX2B in 18 of 29 individuals with CCHS. Most mutations consisted of 5-9 alanine expansions within a 20-residue polyalanine tract probably resulting from non-homologous recombination. We show that PHOX2B is expressed in both the central and the peripheral ANS during human embryonic development. Our data support an essential role of PHOX2B in the normal patterning of the autonomous ventilation system and, more generally, of the ANS in humans.

[Preimplantation genetic diagnosis and its psychological effects]

OBJECTIVE

Report our psychoanalyst experience in clinical practice of pre-implantation genetic diagnosis (PGD).

METHODOLOGY

Between January 1999 and July 2001, 230 couples attended a multidisciplinary PGD consultation and the information meeting that preceded it. Eighty-six of these couples met the team's psychoanalyst during a private encounter (either as couples or individually, depending on their preference).

RESULTS

The development of this technique was capital for couples at risk who, prior to PGD, had often suffered a termination of pregnancy and who may have a child who was seriously ill. Whether they were carriers or affected by the disease, PGD gave them the possibility to react to their condition. Those who have repeatedly been subjected to a painful experience were given the opportunity to play an active part in their own medical history.

CONCLUSION

Beyond the scientific claims of this method, PGD contributes to the healing process of distressed couples and responds to their quest for recognition. We believe that this evolution in preventative medical practice, seen as a positive development, must necessarily lead to a number of ethical as well as psychoanalytical considerations, discussions and interrogations.

[Spectral karyotyping (SKY) principle, avantages and limitations]

Banding karyotype is a routine technique, which allows the identification of numerous aneusomy and/or aneuploïdy in congenital diseases and cancers. However, this analysis fails to detect small or complex chromosome rearrangements. Molecular cytogenetic techniques like fluorescence in situ hybridization (FISH) analysis can overlap these limitations. Particularly, multicolor karyotyping by spectral karyotyping (SKY) may rectify or precise the conventional karyotype results. With two examples, we present here, the principle, the indications and the limits of this technique for constitutional and cancer chromosomal abnormalities characterization. Moreover, we present an easy way to build efficient sky probes with a best sensitivity than the probes classically used.

Reproductive genetic counselling in non-mosaic 47,XXY patients: implications for preimplantation or prenatal diagnosis: Case report and review

With an incidence of approximately 1 in 500 male newborns, the 47,XXY genotype is one the most common sex chromosome anomalies. It is also the most frequent genetic cause of human infertility. Some non-mosaic 47,XXY patients have sperm production which allows infertility treatment to be offered by ICSI. Therefore, the risk of transmitting a chromosome anomaly to the next generation is an important problem in reproductive genetic counselling of these patients. Here, we report on a twin pregnancy where two karyotypically normal neonates 46,XX and 46,XY were born after the use of ICSI in assisted reproduction of a patient with a non-mosaic 47,XXY syndrome. To date, only 38 evolving pregnancies including the present cases, have been reported after ICSI using sperm from non-mosaic 47,XXY patients. Although these data are scarce, they suggest that the risk of chromosome anomaly in the offspring of these patients is low; hence, their reproductive genetic counselling can be reassuring, and management of the pregnancy can proceed with caution.

Mild phenotype in a 15-year-old boy with Pallister-Killian syndrome

Pallister-Killian syndrome is a rare disorder characterized by multiple congenital anomalies, coarse face, pigmentary skin changes, seizures, severe mental retardation, and the presence of an extra metacentric chromosome i(12p) confined to skin fibroblasts only. Here, we report on an unusual case of i(12p) in a 15-year-old boy presenting with mild mental retardation, minor facial features (long face, prognathism, short neck), normal weight, length, and OFC parameters as well as hyperpigmented streaks. The boy attended normal school until the age of 14 years. Because of hyperpigmented stripes, chromosome analysis was performed on skin fibroblasts. This study showed that 37% of the cells had an additional isochromosome for the short arm of chromosome 12. This observation illustrates the phenotypic variability of i(12p) and emphasizes the importance of skin fibroblasts chromosome analysis in patients with pigmentary skin changes.

Molecular characterization of partial trisomy 16q24.1-qter: clinical report and review of the literature

We describe a 3(1/2)-year-old girl with psychomotor and mental retardation; dysmorphic features, including a high forehead with bitemporal narrowing; a broad nasal bridge and a broadened nose; downslanting palpebral fissures; abnormal ears; vertebral abnormalities; cardiac defect; genital hypoplasia; and anal abnormalities. The karyotype of our patient (550 bands) was normal. Molecular cytogenetic techniques, including comparative genomic hybridization (CGH) and fluorescence in situ hybridization (FISH), revealed that this girl was a carrier of a de novo derivative chromosome 7 arising from a cryptic t(7;16)(p22.3;q24.1) translocation generating a trisomy 16q24.1-qter and a 7p22.3-pter deletion. FISH with a series of specific chromosome 7p and 16q probes allowed us to delineate the chromosome 7 breakpoint between YAC660G6 (WD7S517) and YAC848A12 (D7S521, D7S31, and WI-4829) and the chromosome 16 breakpoint between BAC457K7 (D42053) and BAC44201 (SGC30711). The comparison of the clinical features of our patient with those of 2 cases of pure terminal 7p deletion and 28 cases of trisomy 16q reported in the literature allowed us to establish the following phenotype-genotype correlation for trisomy of the long arm of chromosome 16: distinctive facies (high/prominent forehead, bitemporal narrowing, periorbital edema in the neonatal period); severe mental retardation; vertebral, genital, and anal abnormalities to 16q24; distal joint contractures and camptodactyly to 16q23; cleft palate and renal anomalies to 16q22; beaked nose and gall bladder agenesis to 16q21; gut malrotation; lung and liver anomalies to 16q13; and behavior abnormalities to band 16q11-q13.

Truncating neurotrypsin mutation in autosomal recessive nonsyndromic mental retardation

A 4-base pair deletion in the neuronal serine protease neurotrypsin gene was associated with autosomal recessive nonsyndromic mental retardation (MR). In situ hybridization experiments on human fetal brains showed that neurotrypsin was highly expressed in brain structures involved in learning and memory. Immuno-electron microscopy on adult human brain sections revealed that neurotrypsin is located in presynaptic nerve endings, particularly over the presynaptic membrane lining the synaptic cleft. These findings suggest that neurotrypsin-mediated proteolysis is required for normal synaptic function and suggest potential insights into the pathophysiological bases of mental retardation.

[Preimplantation genetic diagnosis: update of the Parisian group]

To report the birth of the first fourteen infants conceived after preimplantation genetic diagnosis (PGD) in our unit. Fifty-nine couples were enrolled between January 2000 and July 2001. They had a total of 71 oocyte pick-up cycles. The collected oocytes were inseminated by intracytoplasmic sperm injection. The resulting embryos were biopsied on the third day of development and the genetic analysis was performed on the same day. Most of the embryo transfers were carried out on the fourth day. The 71 oocyte pick-up cycles yielded 872 oocytes of which 731 were suitable for intracytoplasmic sperm injection. Among the 505 embryos obtained, 421 embryos were biopsied and genetic diagnosis was performed for 312 (74%) of these 127 embryos were transferred during the course of 58 transfer procedures. There were 18 biochemical and 12 ongoing (7 singles, 4 twins and 1 triple) pregnancies. Sixteen infants have been born and 2 are expected. PGD has gained a place among the choices offered to couples at risk of transmission of a serious and incurable genetic disease.

Overgrowth and trisomy 15q26.1-qter including the IGF1 receptor gene: report of two families and review of the literature

Overgrowth is rarely associated with chromosomal imbalances. Here we report on four children from two unrelated families presenting with overgrowth and a terminal duplication of the long arm of chromosome 15 diagnosed using cytogenetic and FISH studies. In both cases, chromosome analysis of the parents showed a balanced translocation involving 15q26.1-qter. Molecular and cytogenetic studies showed three copies of the insulin-like growth factor 1 receptor (IGF1R) gene. This finding suggests that overgrowth observed in our patients might be causally related to a dosage effect of the IGF1R gene, in contrast to severe growth retardation observed in patients with terminal deletion of 15q. The present observation emphasises the importance of chromosome analysis in patients with overgrowth and mental retardation. Moreover, it further delineates a specific phenotype related to trisomy 15q26.1-qter with macrosomia at birth, overgrowth, macrocephaly and mild developmental delay being the major clinical features.

[Parental age and genetic risks for the offspring]

Despite numerous studies, the age-related risk of genetic defects in the offspring remains poorly understood. It is clear that the frequency at birth of some mendelian disorders is related to advanced paternal age, but this relationship is heterogeneous and varies from one disorder to another. Similarly, it has been proposed that among commonly observed birth defects, a subgroup of cases may be due to new unrecognized dominant mutations of paternal origin. Finally, despite many years of enquiry, increasing maternal age remains the only incontrovertible factor associated with human aneuploidy.

[Preimplantation genetic diagnosis experience in Paris: evaluation of first births]

OBJECTIVE

To report the birth of the first fourteen infants conceived after preimplantation genetic diagnosis (PGD) in our unit.

PATIENTS AND METHODS

Fifty-nine couples were enrolled between January 2000 and July 2001. They had a total of 71 oocyte pick-up cycles. The collected oocytes were inseminated by intracytoplasmic sperm injection. The resulting embryos were biopsied on the third day of development and the genetic analysis was performed on the same day. Most of the embryo transfers were carried out on the fourth day.

RESULTS

The 71 oocyte pick-up cycles yielded 872 oocytes of which 731 were suitable for intacytoplasmic sperm injection. Among the 505 embryos obtained, 421 embryos were biopsied and genetic diagnosis was performed for 312 (74%) of these. 127 embryos were transferred during the course of 58 transfer procedures. There were 18 biochemical and 12 ongoing (7 singles, 4 twins and 1 triple) pregnancies. Fourteen infants have been born and 2 are expected.

CONCLUSION

PGD has gained a place among the choices offered to couples at risk of transmission of a serious and incurable genetic disease.

Expression and mutation analysis of BRUNOL3, a candidate gene for heart and thymus developmental defects associated with partial monosomy 10p

Partial monosomy 10p is a rare chromosomal aberration. Patients often show symptoms of the DiGeorge/velocardiofacial syndrome spectrum. The phenotype is the result of haploinsufficiency of at least two regions on 10p, the HDR1 region associated with hypoparathyroidism, sensorineural deafness, and renal defects (HDR syndrome) and the more proximal region DGCR2 responsible for heart defects and thymus hypoplasia/aplasia. While GATA3 was identified as the disease causing gene for HDR syndrome, no genes have been identified thus far for the symptoms associated with DGCR2 haploinsufficiency. We constructed a deletion map of partial monosomy 10p patients and narrowed the critical region DGCR2 to about 300 kb. The genomic draft sequence of this region contains only one known gene, BRUNOL3 ( NAPOR, CUGBP2, ETR3). In situ hybridization of human embryos and fetuses revealed as well as in other tissues a strong expression of BRUNOL3 in thymus during different developmental stages. BRUNOL3 appears to be an important factor for thymus development and is therefore a candidate gene for the thymus hypoplasia/aplasia seen in partial monosomy 10p patients. We did not find BRUNOL3 mutations in 92 DiGeorge syndrome-like patients without chromosomal deletions and in 8 parents with congenital heart defect children.

Birth of healthy female twins after preimplantation genetic diagnosis of cystic fibrosis combined with gender determination

Two healthy sisters with a familial history of mental retardation were referred to our centre for preimplantation genetic diagnosis (PGD). Their two brothers showed severe mental retardation. The molecular basis for their disorder could not be identified, but one of the sisters and the mother presented a highly skewed pattern of X-inactivation reinforcing the likelihood of an X-linked mode of inheritance. Both sisters requested PGD to avoid the abortion of potentially affected male fetuses. PGD for sex by fluorescent in-situ hybridization was carried out for the first sister and resulted in the birth of a female child. The second sister and her partner, whose niece had cystic fibrosis (CF), were tested for CF mutations, and were both found to be deltaF508 heterozygous. We developed an efficient single cell PCR protocol for the simultaneous amplification of the CF (deltadeltaF508) locus as well as the X-linked amelogenin gene and its highly homologous pseudogene on the Y chromosome. Two PGD cycles were carried out to screen against male and deltaF508 homozygous deleted embryos. In each case several embryos could be selected for transfer and the second cycle resulted in a twin pregnancy followed by the birth of two healthy female infants.

Expression of the SMADIP1 gene during early human development

The smad binding protein 1 gene (SMADIP1, MIM 605802) has been recently identified as a disease causing gene in a polytopic embryonic defect (MIM 235730) including midline anomalies, facial dysmorphic features and enteric nervous system malformation (Hirschsprung disease). To confirm the pleiotropic role of SMADIP1 during embryogenesis and investigate its role in neural crest cell derivatives differentiation, we performed RNA in situ hybridization at early stages of human development. According to the spectrum of malformations observed in patients, expression of SMADIP1 is observed in neural crest derived cells (peripheric nervous system, enteric nervous system, facial neurectoderm and cranial nerve ganglia), central nervous system, genital tubercle, muscles and kidneys. Surprisingly, SMADIP1 expression is also found in limbs and developing eye. Although congenital heart defects are frequently observed in patients with either a SMADIP1 large scale deletion or truncating mutation, no SMADIP1 expression could be detected in the developing heart at the stages studied.

Automated fluorescent genotyping detects 10% of cryptic subtelomeric rearrangements in idiopathic syndromic mental retardation

Recent studies have shown that cryptic unbalanced subtelomeric rearrangements contribute to a significant proportion of idiopathic syndromic mental retardation cases. Using a fluorescent genotyping based strategy, we found a 10% rate of cryptic subtelomeric rearrangements in a large series of 150 probands with severe idiopathic syndromic mental retardation and normal RHG-GTG banded karyotype. Fourteen children were found to carry deletions or duplications of one or more chromosome telomeres and two children had uniparental disomy. This study clearly shows that fluorescent genotyping is a sensitive and cost effective method that not only detects cryptic subtelomeric rearrangements but also provides a unique opportunity to detect uniparental disomies. We suggest giving consideration to systematic examination of subtelomeric regions in the diagnostic work up of patients with unexplained syndromic mental retardation.