A French collaborative survey of 272 fetuses with 22q11.2 deletion: ultrasound findings, fetal autopsies and pregnancy outcomes.

OBJECTIVE: The 22q11.2 deletion (del22q11.2) is one of the most common microdeletions. We performed a collaborative, retrospective analysis in France of prenatal diagnoses and outcomes of fetuses carrying the del22q11.2. METHODS: A total of 272 fetuses were included. Data on prenatal diagnosis, ultrasound findings, pathological features, outcomes and inheritance were analyzed. RESULTS: The mean time of prenatal diagnosis was 25.6 ± 6 weeks of gestation. Most of the diagnoses (86.8%) were prompted by abnormal ultrasound findings [heart defects (HDs), in 83.8% of cases]. On fetal autopsy, HDs were again the most common disease feature, but thymus, kidney abnormalities and facial dysmorphism were also described. The deletion was inherited in 27% of cases. Termination of pregnancy (TOP) occurred in 68.9% of cases and did not appear to depend on the inheritance status. However, early diagnosis was associated with a higher TOP rate. CONCLUSION: This is the largest cohort of prenatal del22q11.2 diagnoses. As in postnatally diagnosed cases, HDs were the most frequently observed abnormalities. However, thymus and kidney abnormalities and polyhydramnios should also be screened for in the prenatal diagnosis of del22q11.2. Only the time of diagnosis appeared to be strongly associated with the pregnancy outcome: the earlier the diagnosis, the higher the TOP rate.

SHOX mutations in dyschondrosteosis (Leri-Weill syndrome).

Dyschondrosteosis (DCS) is an autosomal dominant form of mesomelic dysplasia with deformity of the forearm (Madelung deformity; ref. 3). Based on the observation of XY translocations (p22,q12; refs 4-6) in DCS patients, we tested the pseudoautosomal region in eight families with DCS and showed linkage of the DCS gene to a microsatellite DNA marker at the DXYS233 locus (Zmax=6.26 at theta=0). The short stature homeobox-containing gene (SHOX), involved in idiopathic growth retardation and possibly Turner short stature, maps to this region and was therefore regarded as a strong candidate gene in DCS. Here, we report large-scale deletions (in seven families) and a nonsense mutation (in one family) of SHOX in patients with DCS and show that Langer mesomelic dwarfism results from homozygous mutations at the DCS locus.

The human necdin gene, NDN, is maternally imprinted and located in the Prader-Willi syndrome chromosomal region.

Prader-Willi syndrome (PWS) is a neurogenetic disorder that results from the absence of a normal paternal contribution to the 15q11-13 region. The clinical manifestations of PWS are a transient severe hypotonia in the newborn period, with mental retardation, hypogonadism and obesity observed later in development. Five transcripts with exclusive expression from the paternal allele have been isolated, but none of these has been shown to be involved in PWS. In this study, we report the isolation and characterization of NDN, a new human imprinted gene. NDN is exclusively expressed from the paternal allele in the tissues analysed and is located in the PWS region. It encodes a putative protein homologous to the mouse brain-specific NECDIN protein, NDN; as in mouse, expression in brain is restricted to post-mitotic neurons. NDN displays several characteristics of an imprinted locus, including allelic DNA methylation and asynchronous DNA replication. A complete lack of NDN expression in PWS brain and fibroblasts indicates that the gene is expressed exclusively from the paternal allele in these tissues and suggests a possible role of this new gene in PWS.

Novel FOXG1 mutations associated with the congenital variant of Rett syndrome.

BACKGROUND: Rett syndrome is a severe neurodevelopmental disorder representing one of the most common genetic causes of mental retardation in girls. The classic form is caused by MECP2 mutations. In two patients affected by the congenital variant of Rett we have recently identified mutations in the FOXG1 gene encoding a brain specific transcriptional repressor, essential for early development of the telencephalon. METHODS: 60 MECP2/CDKL5 mutation negative European Rett patients (classic and variants), 43 patients with encephalopathy with early onset seizures, and four atypical Rett patients were analysed for mutations in FOXG1. RESULTS AND CONCLUSIONS: Mutations have been identified in four patients, independently classified as congenital Rett variants from France, Spain and Latvia. Clinical data have been compared with the two previously reported patients with mutations in FOXG1. In all cases hypotonia, irresponsiveness and irritability were present in the neonatal period. At birth, head circumference was normal while a deceleration of growth was recognised soon afterwards, leading to severe microcephaly. Motor development was severely impaired and voluntary hand use was absent. In contrast with classic Rett, patients showed poor eye contact. Typical stereotypic hand movements with hand washing and hand mouthing activities were present continuously. Some patients showed abnormal movements of the tongue and jerky movements of the limbs. Brain magnetic resonance imaging showed corpus callosum hypoplasia in most cases, while epilepsy was a variable sign. Scoliosis was present and severe in the older patients. Neurovegetative symptoms typical of Rett were frequently present.

Spectrum and distribution of MECP2 mutations in 424 Rett syndrome patients: a molecular update.

Mutations in the MECP2 (Methyl-CpG-binding protein) gene have been reported to cause Rett syndrome (RTT), an X-linked progressive encephalopathy. Recent studies have identified large gene rearrangements that escape the common PCR-based mutation screening strategy and mutations in a novel MeCP2 isoform (named MECP2B). We have collected the results of MECP2 mutational analysis concerning 424 RTT patients conducted in eight laboratories in France. In total, 121 different MECP2 mutations were identified. R168X (11.5%) is the most common of MECP2 mutations, followed by R270X (9%), R255X (8.7%), T158 M (8.3%) and R306C (6.8%). Only eight mutations had relative frequency>3%. Large and complex rearrangements not previously detected using only a PCR-based strategy represent 5.8% of MECP2 mutations. On the contrary, mutation in exon 1 appears to be rare (less than 0.5%). These data demonstrate the high allelic heterogeneity of RTT in France and suggest that routine mutation screening in MECP2 should include quantitative analysis of the MECP2 gene. This study represents an important instrument for molecular diagnosis strategy and genetic counseling in RTT families.

DNMT3B mutations and DNA methylation defect define two types of ICF syndrome.

ICF syndrome is a rare autosomal recessive disease characterized by variable immunodeficiency, centromeric instability, and facial abnormalities. Mutations in the catalytic domain of DNMT3B, a gene encoding a de novo DNA methyltransferase, have been recognized in a subset of patients. ICF syndrome is a genetic disease directly related to a genomic methylation defect that mainly affects classical satellites 2 and 3, both components of constitutive heterochromatin. The variable incidence of DNMT3B mutations and the differential methylation defect of alpha satellites allow the identification of two types of patients, both showing an undermethylation of classical satellite DNA. This classification illustrates the specificity of the methylation process and raises questions about the genetic heterogeneity of the ICF syndrome.

Clinical heterogeneity in 16 patients with inv dup 15 chromosome: cytogenetic and molecular studies, search for an imprinting effect.

We report on clinical, cytogenetic and molecular analyses of 16 patients with inv dup (15) chromosome. We define the content of the inv dup (15) markers, their meiotic origin and the methylation status of the chromosome region involved. Precise phenotype-karyotype-genotype correlations allowed the identification of five different types of marker and demonstrated that even when the molecular content of the inv dup (15) chromosome clearly contributes to the severity of the phenotype, it does not appear to be the only relevant factor. All the markers were of maternal origin with an identical methylation profile, and neither imprinting nor methylation can explain the phenotypic variability. We suggest that the degree of phenotypic severity may be correlated with the severity of epilepsy.

Unexpected inheritance of the (CGG)n trinucleotide expansion in a fragile X syndrome family.

The fragile X syndrome is the most frequent cause of inherited mental retardation. CGG repeat alleles are usually classified as normal, premutation, or full mutation based on the length of this triplet in the 5' untranslated region of the FMR1 gene. The pattern of inheritance follows a two-stage intergenerational process in which the premutation evolves into the full mutation. Some reverse mutations have been described, but they appear to be very rare. We describe a family in which a mother of two affected males herself carried a full mutation. Surprisingly, her clinically normal daughter, initially considered to be a carrier by linkage analysis, carried a very short premutation. Findings from our family study corroborate the hypothesis that the expansion during female transmission could be a postzygotic event and raise the problem of mosaicism.

Phenotype-genotype correlation in 20 deletion and 20 non-deletion Angelman syndrome patients.

Angelman syndrome (AS) is a neurodevelopmental disorder caused by the absence of a maternal contribution to chromosome 15q11-q13. There are four classes of AS according to molecular or cytogenetic status: maternal microdeletion of 15q11-q13 (approximately 70% of AS patients); uniparental disomy (UPD); defects in a putative imprinting centre (IM); the fourth includes 20-30% of AS individuals with biparental inheritance and a normal pattern of allelic methylation in 15q11-q13. Mutations of UBE3A have recently been identified as causing AS in the latter group. Few studies have investigated the phenotypic differences between these classes. We compared 20 non-deletion to 20 age-matched deletion patients and found significant phenotypic differences between the two groups. The more severe phenotype in the deletion group may suggest a contiguous gene syndrome.

Origin of nondisjunction in trisomy 8 and trisomy 8 mosaicism.

Causes of chromosomal nondisjunction is one of the remaining unanswered questions in human genetics. In order to increase our understanding of the mechanisms underlying nondisjunction we have performed a molecular study on trisomy 8 and trisomy 8 mosaicism. We report the results on analyses of 26 probands (and parents) using 19 microsatellite DNA markers mapping along the length of chromosome 8. The 26 cases represented 20 live births, four spontaneous abortions, and two prenatal diagnoses (CVS). The results of the nondisjunction studies show that 20 cases (13 maternal, 7 paternal) were probably due to mitotic (postzygotic) duplication as reduction to homozygosity of all informative markers was observed and as no third allele was ever detected. Only two cases from spontaneous abortions were due to maternal meiotic nondisjunction. In four cases we were not able to detect the extra chromosome due to a low level of mosaicism. These results are in contrast to the common autosomal trisomies (including mosaics), where the majority of cases are due to errors in maternal meiosis.

Prader-Willi syndrome: diagnostic strategy with a cytogenetic and molecular approach.

Prader-Willi syndrome (PWS) is a disorder characterized by neonatal hypotonia with poor suck, mild to moderate mental retardation, obesity beginning after 3 yr of age, hypogonadism and characteristic facial features. High resolution cytogenetic studies showed a deletion of the proximal chromosome 15q(q11-q13) region in approximately 50%. Interestingly, the same deletion was described in another distinct mental disorder: the Angelman syndrome (AS). This deletion was confirmed by molecular analyses, and a new mechanism was reported: uniparental disomy (maternal in PWS and paternal in AS) strongly implicate genomic imprinting in this chromosomal region. The principal aim of our group is to apply cytogenetic and molecular biology techniques to perform diagnosis and genetic counselling. Patient studies were usually based on high resolution cytogenetic analysis, quantitative Southern blotting (with D15S9, D15S11, D15S10, D15S12 loci) and dinucleotide repeat polymorphism assay by polymerase chain reaction (PCR) (IR4 .3R and GABARB3). The combination of these different methods allowed us to propose a diagnostic strategy for PWS.

Fragile X syndrome and 22q11.2 microdeletion in the same sibship.

We present a family with an unusual association of two frequent genetic disorders, 22q11.2 microdeletion and fragile X syndrome, originating from the same parent. Our observation confirms the wide intrafamilial clinical variability of the 22q11.2 microdeletion and illustrates the difficulty of the clinical diagnosis for the fragile X syndrome in affected females.

Microcephalic osteodysplastic primordial dwarfism Taybi-Linder type: report of four cases and review of the literature.

Microcephalic and osteodysplastic primordial dwarfism (MODP) types I, II, and III were defined by Majewski et al. in 1982. This group of syndromes was characterized by intrauterine growth retardation, microcephaly, and typical facial appearance with prominent nose and micrognathia. Type II was clearly different, both clinically and radiologically, whereas types I and III shared manifestations. Distinction between the latter two was established on the basis of subtle radiological differences. In 1967, Taybi and Linder described another syndrome with microcephalic congenital dwarfism. There is a consensus that MODP type I and III and Taybi-Linder cephaloskeletal dysplasia represent the same disorder. We report on four patients with MODP type Taybi-Linder syndromes, two of whom were born to unrelated but consanguineous parents, while the other two were sibs. Second-trimester prenatal detection by ultrasonography was possible in one case. Consanguinity in two cases and recurrence among sibs are consistent with autosomal recessive inheritance.

X-linked mental retardation with neonatal hypotonia in a French family (MRX15): gene assignment to Xp11.22-Xp21.1.

Linkage analysis was performed in a family with non-specific X-linked mental retardation (MRX 15). Hypotonia in infancy was the most remarkable physical manifestation. The severity of mental deficiency was variable among the patients, but all of them had poor or absent speech. Significant lod scores at a recombination fraction of zero were detected with the marker loci DXS1126, DXS255, and DXS573 (Zmax = 2.01) and recombination was observed with the two flanking loci DXS164 (Xp21.1) and DXS988 (Xp11.22), identifying a 17 cM interval. This result suggests a new gene localization in the proximal Xp region. In numerous families with non-specific X-linked mental retardation (MRX), the corresponding gene has been localized to the paracentromeric region in which a low recombination rate impairs the precision of mapping.

Multiple lateral meningoceles, distinctive facies and skeletal anomalies: a new case of Lehman syndrome.

We describe a 19-year-old boy who presented with facial dysmorphism, multiple lateral meningoceles, skeletal abnormalities and normal intelligence. Neurofibromatosis and Marfan syndrome were excluded. Electron microscopy of the skin showed non-specific abnormalities suggesting a connective tissue disorder. The features of this boy closely resemble those in a mother and daughter with Lehman syndrome.

Congenital bowing of the long bones in two fetuses presenting features of Stüve-Wiedemann syndrome and Schwartz-Jampel syndrome type 2.

We report two fetuses with congenital bowing of the long bones. Clinical and radiological features led us to consider two conditions: the Stüve-Wiedemann syndrome and the neonatal Schwartz-Jampel syndrome type 2. Similarities between the two syndromes are discussed.

Kabuki make-up (Niikawa-Kuroki) syndrome: a study of 16 non-Japanese cases.

Kabuki make-up (Niikawa-Kuroki) syndrome has been described mainly in Japanese patients. In this paper we report sixteen new cases from Europe and North America, suggesting that Kabuki make-up syndrome may be more common outside of Japan than supposed. Their features are compared with those of the Japanese patients and most of our findings are similar to those previously reported. The facial phenotype is specific and easily recognizable, regardless of ethnic origin. Postnatal growth retardation and mild mental retardation are confirmed to be cardinal manifestations of the syndrome. Skeletal anomalies were present in all cases but most of the radiological changes were non-specific. The specificity of metacarpophalangeal pattern profile is not confirmed. Conversely, dermatoglyphic analysis is helpful in the diagnosis of this condition. Two differences have emerged between the Japanese patients and those in this study. Firstly, two-thirds of the patients in this series had significant neurological dysfunction other than mental retardation. Secondly, joint hypermobility appears more common in non-Japanese patients. Confirmation of these findings requires further studies.

SHOX gene mutations and deletions in dyschondrosteosis or Leri-Weill syndrome.

Dyschondrosteosis is an autosomal dominant form of mesomelic dysplasia that is often combined with a deformity of the forearms called Madelung deformity. Based on the observation of X-Y translocations (p22,q12) in patients with dyschondrosteosis, the authors tested the pseudoautosomal region in eight affected families and showed linkage of the dyschondrosteosis gene to a microsatellite DNA marker at the DXYS233 locus (Zmax = 6.26 at theta = 0). Since the short stature homeobox-containing gene (SHOX) involved in idiopathic growth retardation and possibly Turner syndrome maps to this region, SHOX was regarded as a strong candidate gene for dyschondrosteosis. This article reports the detection of large-scale SHOX deletions in seven of the eight families and a nonsense mutation of SHOX in the remaining family affected with dyschondrosteosis. Additional evidence suggests that Langer mesomelic dwarfism results from homozygous mutations at the genetic locus responsible for dyschondrosteosis.

[Clinical approach to mental retardation of genetic origin]. / Approche clinique des retards mentaux d'origine génétique.

Etiological investigations of mental deficiencies and their syndromic analysis have greatly progressed with advancing knowledge in the field of genetics and the advent of new technical procedures. Fast diagnostic tests are now available for certain syndromes, particularly those related to micordeletions. Clinical diagnosis remains however the necessary prerequisite for ordering such tests. The clinical examination not only provides a detailed description of the physical condition, but also provides essential information on behavioral and cognitive disorders. Distinctive behavioral patterns observed in some syndromes are suggestive of a "behavioral phenotype". This pattern can be a valuable clue to diagnosis and also allows for early intervention and counselling specifically aimed at dealing with predicted behavioral abnormalities.

[Smith-Magenis syndrome]. / Syndrome de Smith-Magenis.

BACKGROUND: The main features of the Smith-Magenis syndrome include broad flat midface, brachycephaly, broad nasal bridge, brachydactyly, hoarse deep voice, speech and developmental delay, and behavioral anomalies. This syndrome is due to interstitial deletion of chromosome 17p11.2. CASE REPORT: A 7-year-old girl was admitted for mental retardation. Clinical examination showed brachycephaly, broad flat midface, broad nasal bridge, malar hypoplasia, brachydactyly, decreased or absent deep tendon reflexes, and hoarse deep voice. She had a mild deafness, behavioral problems, and sleep disturbances. Chromosome analysis on lymphocytes identified a microdeletion of one chromosome subband 17p11.2. Molecular studies indicated loss of maternal allele. CONCLUSION: The Smith-Magenis syndrome is probably underdiagnosed because of its usually mild clinical features. High-resolution chromosome analysis is needed for diagnosis.