Benign familial infantile convulsions: mapping of a novel locus on chromosome 2q24 and evidence for genetic heterogeneity.

In 1997, a locus for benign familial infantile convulsions (BFIC) was mapped to chromosome 19q. Further data suggested that this locus is not involved in all families with BFIC. In the present report, we studied eight Italian families and mapped a novel BFIC locus within a 0.7-cM interval of chromosome 2q24, between markers D2S399 and D2S2330. A maximum multipoint HLOD score of 6.29 was obtained under the hypothesis of genetic heterogeneity. Furthermore, the clustering of chromosome 2q24-linked families in southern Italy may indicate a recent founder effect. In our series, 40% of the families are linked to neither chromosome 19q or 2q loci, suggesting that at least three loci are involved in BFIC. This finding is consistent with other autosomal dominant idiopathic epilepsies in which different genes were found to be implicated.

Clinical and molecular characterisation of 80 patients with 5p deletion: genotype-phenotype correlation.

The majority of deletions of the short arm of chromosome 5 are associated with cri du chat syndrome (CdCS) and patients show phenotypic and cytogenetic variability. To perform a genotype-phenotype correlation, 80 patients from the Italian CdCS Register were analysed. Molecular cytogenetic analysis showed that 62 patients (77.50%) had a 5p terminal deletion characterised by breakpoint intervals ranging from p13 (D5S763) to p15.2 (D5S18). Seven patients (8.75%) had a 5p interstitial deletion, four (5%) a de novo translocation, and three (3.75%) a familial translocation. Of the remaining four patients, three (3.75%) had de novo 5p anomalies involving two rearranged cell lines and one (1.25%) had a 5p deletion originating from a paternal inversion. The origin of the deleted chromosome 5 was paternal in 55 out of 61 patients (90.2%). Genotype-phenotype correlation in 62 patients with terminal deletions highlighted a progressive severity of clinical manifestation and psychomotor retardation related to the size of the deletion. The analysis of seven patients with interstitial deletions and one with a small terminal deletion confirmed the existence of two critical regions, one for dysmorphism and mental retardation in p15.2 and the other for the cat cry in p15.3. Results from one patient permitted the cat cry region to be distally narrowed from D5S13 to D5S731. Furthermore, this study lends support to the hypothesis of a separate region in p15.3 for the speech delay.

X-linked neonatal diabetes mellitus, enteropathy and endocrinopathy syndrome is the human equivalent of mouse scurfy.

To determine whether human X-linked neonatal diabetes mellitus, enteropathy and endocrinopathy syndrome (IPEX; MIM 304930) is the genetic equivalent of the scurfy (sf) mouse, we sequenced the human ortholog (FOXP3) of the gene mutated in scurfy mice (Foxp3), in IPEX patients. We found four non-polymorphic mutations. Each mutation affects the forkhead/winged-helix domain of the scurfin protein, indicating that the mutations may disrupt critical DNA interactions.

Familial infantile myoclonic epilepsy: clinical features in a large kindred with autosomal recessive inheritance.

PURPOSE: To describe the clinical features of a large kindred with familial infantile myoclonic epilepsy (FIME) with autosomal recessive inheritance, and to discuss the nosology of the early infantile myoclonic epilepsies (IMEs). METHODS: The family descends from the intermarriage of two couples of siblings. In a previous study, we mapped the genetic locus to chromosome 16p13. We analyzed results of family records and personal history, psychomotor development, neurologic examination, epilepsy features, and EEG recordings for each subject. RESULTS: FIME has a strong penetrance (eight affected of 14 subjects) and a homogeneous clinical picture. Like the benign form of infantile myoclonic epilepsy (BIME), FIME is a true idiopathic IME with unremarkable history, no neurologic or mental impairment, good response to treatment, and normal interictal EEG pattern. Conversely, onset with generalized epileptic seizures without fever (four patients) or with fever (one patient), frequency and duration of the myoclonic seizures, occurrence of generalized tonic--clonic seizures (GTCSs) in all patients and persistence of seizures into adulthood are characteristics of the severe infantile myoclonic epilepsy (SIME). CONCLUSIONS: Clinical overlap probably exists among the myoclonic epilepsies of infancy. FIME differs from other forms of IME in its phenotypic features. The peculiar mode of inheritance is explained by the genetic background of the family. Genetic studies suggest linkage to chromosome 16 in familial cases of true IME.

Caveolin-3 directly interacts with the C-terminal tail of beta -dystroglycan. Identification of a central WW-like domain within caveolin family members.

Caveolin-3, the most recently recognized member of the caveolin gene family, is muscle-specific and is found in both cardiac and skeletal muscle, as well as smooth muscle cells. Several independent lines of evidence indicate that caveolin-3 is localized to the sarcolemma, where it associates with the dystrophin-glycoprotein complex. However, it remains unknown which component of the dystrophin complex interacts with caveolin-3. Here, we demonstrate that caveolin-3 directly interacts with beta-dystroglycan, an integral membrane component of the dystrophin complex. Our results indicate that caveolin-3 co-localizes, co-fractionates, and co-immunoprecipitates with a fusion protein containing the cytoplasmic tail of beta-dystroglycan. In addition, we show that a novel WW-like domain within caveolin-3 directly recognizes the extreme C terminus of beta-dystroglycan that contains a PPXY motif. As the WW domain of dystrophin recognizes the same site within beta-dystroglycan, we also demonstrate that caveolin-3 can effectively block the interaction of dystrophin with beta-dystroglycan. In this regard, interaction of caveolin-3 with beta-dystroglycan may competitively regulate the recruitment of dystrophin to the sarcolemma. We discuss the possible implications of our findings in the context of Duchenne muscular dystrophy.

Mutation in the CAV3 gene causes partial caveolin-3 deficiency and hyperCKemia.

Mutations in the caveolin-3 (CAV3) gene are associated with autosomal dominant limb-girdle muscular dystrophy (LGMD1C). The authors report a novel sporadic mutation in the CAV3 gene in two unrelated children with persistent elevated levels of serum creatine kinase (hyperCKemia) without muscle weakness. Immunohistochemistry and quantitative immunoblot analysis of caveolin-3 showed reduced expression of the protein in muscle fibers. Our data indicate that a partial caveolin-3 deficiency should be considered in the differential diagnosis of idiopathic hyperCKemia.

FRAXE mutation in a mentally retarded subject and in his phenotypically normal twin brother.

The FRAXE fragile site, 600 kb distal to the more common FRAXA, has been reported to be expressed in subjects with mild non-syndromal mental retardation (MR). Amplification of more than 200 GCC repeats, associated with methylation of the adjacent CpG island at Xq28, leads to the expression of the fragile site. In 1996 a large gene, FMR2, transcribed distally from the CpG island and downregulated by repeat expansion and methylation, was identified. Among 232 mentally retarded patients, tested FRAXA negative, we identified an Italian family segregating a hypermethylated expansion at the FRAXE locus in two dizygotic twin brothers, their sister and their mother. The index case was referred at 23 years of age with severe MR, epilepsy, a dysmorphic face with a high arched palate, marfanoid habitus and hyperreflexia of the lower limbs. His brother was referred to as normal and psychometric tests confirmed he is not mentally retarded. All members of the family underwent FRAXE molecular analysis, after cytogenetic expression of the fraX site and negative FRAXA test. Interestingly, an expansion and a hypermethylation at the FRAXE locus were found in all of them. Fibroblasts from the clinically normal brother were assayed for FMR2 expression and the transcription of the gene was found to be silenced. The presence of a phenotypically normal male with absent FMR2 expression in fibroblasts suggests that the relationship between the FRAXE mutation, FMR2 expression and MR needs to be further investigated.

Mapping of a locus for a familial autosomal recessive idiopathic myoclonic epilepsy of infancy to chromosome 16p13.

Myoclonic epilepsies with onset in infancy and childhood are clinically and etiologically heterogeneous. Although genetic factors are thought to play an important role, to date very little is known about the etiology of these disorders. We ascertained a large Italian pedigree segregating a recessive idiopathic myoclonic epilepsy that starts in early infancy as myoclonic seizures, febrile convulsions, and tonic-clonic seizures. We typed 304 microsatellite markers spanning the 22 autosomes and mapped the locus on chromosome 16p13 by linkage analysis. A maximum LOD score of 4.48 was obtained for marker D16S3027 at recombination fraction 0. Haplotype analysis placed the critical region within a 3.4-cM interval between D16S3024 and D16S423. The present report constitutes the first example of an idiopathic epilepsy that is inherited as an autosomal recessive trait.

No evidence of a major locus for benign familial infantile convulsions on chromosome 19q12-q13.1.

PURPOSE: A locus for benign familial convulsions (BFICs) has been recently mapped on chromosome 19q12-13.1 by studying five families of Italian descent. The main goal of this study was to investigate the role of this locus in a set of seven newly identified families with at least three affected cases. METHODS: Five polymorphic microsatellite markers covering the BFIC locus on chromosome 19q have been typed, and parametric linkage analysis has been performed to analyze the segregation of the BFIC locus within our families. RESULTS: Cumulative 2-point lod scores and multipoint analysis showed no evidence of linkage between chromosome 19 markers and the BFIC phenotype. The analysis of family-specific 2-point lod scores and haplotypes, however, indicated the presence of linkage to chromosome 19q in a single family, suggesting genetic heterogeneity within our family sample. CONCLUSIONS: Our study demonstrates that the previously reported BFIC locus on chromosome 19q12-13.1 is not a major locus for BFICs. We suggest that genetic heterogeneity may have generated our discordant linkage findings, as it was reported in benign familial neonatal convulsions, a related idiopathic mendelian syndrome.

Mosaicism for the full mutation and a microdeletion involving the CGG repeat and flanking sequences in the FMR1 gene in eight fragile X patients.

The molecular mechanism of the fragile X syndrome is based on the expansion of an unstable CGG repeat in the 5' untranslated region of the FMR1 gene in most patients. This expansion is associated with an abnormal DNA methylation leading to the absence of production of FMR1 protein (FMRP). Such expansion apparently predisposes the repeat and flanking regions to further instability that may lead to mosaic conditions with a full mutation and a premutation or, rarely, with normal or reduced alleles that can sometimes be transcriptionally active. In this study we describe eight unrelated fragile X patients who are mosaic for both a full mutation and an allele of normal (four cases) or reduced size (four cases). Sequencing analysis of the deletion breakpoints in 6 patients demonstrated an internal deletion confined to the CGG repeat in four of them, which represents the most likely explanation for the regression of the full mutation to a normal sized allele. In two patients with a reduced allele, the deletion encompassed the entire CGG repeat and part of the flanking regions. Analysis of FMRP by Western blot was performed in one of the mosaics with a normal sized allele and in three of those with a reduced allele. In the first patient's lymphocytes FMRP was detected, whereas in the three other patients the deletion is likely to impair transcription as no FMRP was present in their lymphocytes.

Mutations in the caveolin-3 gene cause autosomal dominant limb-girdle muscular dystrophy.

Limb-girdle muscular dystrophy (LGMD) is a clinically and genetically heterogeneous group of myopathies, including autosomal dominant and recessive forms. To date, two autosomal dominant forms have been recognized: LGMD1A, linked to chromosome 5q, and LGMD1B, associated with cardiac defects and linked to chromosome 1q11-21. Here we describe eight patients from two different families with a new form of autosomal dominant LGMD, which we propose to call LGMD1C, associated with a severe deficiency of caveolin-3 in muscle fibres. Caveolin-3 (or M-caveolin) is the muscle-specific form of the caveolin protein family, which also includes caveolin-1 and -2. Caveolins are the principal protein components of caveolae (50-100 nm invaginations found in most cell types) which represent appendages or sub-compartments of plasma membranes. We localized the human caveolin-3 gene (CAV3) to chromosome 3p25 and identified two mutations in the gene: a missense mutation in the membrane-spanning region and a micro-deletion in the scaffolding domain. These mutations may interfere with caveolin-3 oligomerization and disrupt caveolae formation at the muscle cell plasma membrane.

Mutational analysis of the SOX9 gene in campomelic dysplasia and autosomal sex reversal: lack of genotype/phenotype correlations.

It has previously been shown that, in the heterozygous state, mutations in the SOX9 gene cause campomelic dysplasia (CD) and the often associated autosomal XY sex reversal. In 12 CD patients, 10 novel mutations and one recurrent mutation were characterized in one SOX9 allele each, and in one case, no mutation was found. Four missense mutations are all located within the high mobility group (HMG) domain. They either reduce or abolish the DNA-binding ability of the mutant SOX9 proteins. Among the five nonsense and three frameshift mutations identified, two leave the C-terminal transactivation (TA) domain encompassing residues 402-509 of SOX9 partly or almost completely intact. When tested in cell transfection experiments, the recurrent nonsense mutation Y440X, found in two patients who survived for four and more than 9 years, respectively, exhibits some residual transactivation ability. In contrast, a frameshift mutation extending the protein by 70 residues at codon 507, found in a patient who died shortly after birth, showed no transactivation. This is apparently due to instability of the mutant SOX9 protein as demonstrated by Western blotting. Amino acid substitutions and nonsense mutations are found in patients with and without XY sex reversal, indicating that sex reversal in CD is subject to variable penetrance. Finally, none of 18 female patients with XY gonadal dysgenesis (Swyer syndrome) showed an altered SOX9 banding pattern in SSCP assays, providing evidence that SOX9 mutations do not usually result in XY sex reversal without skeletal malformations.

Combined use of cytogenetic analysis and FISH for the identification of two antenatal de novo markers as Robertsonian translocations involving the p arms.

In two prenatal cases, de novo nonmosaic bisatellited marker chromosomes were studied with the combined use of fluorescence in situ hybridization (FISH) with chromosome specific probes and cytogenetic heteromorphisms. The FISH studies showed that one of the small accessory chromosome could be a heterozygous 14/15 or 15/22 translocation involving the p arms of these chromosomes, the other showed only one hybridization spot with the classical satellite probe of chromosome 15. The analysis of heteromorphisms of the parental acrocentric chromosomes demonstrated that the two markers were Robertsonian translocations involving in the first case the p arms of the maternal 15 and 22 chromosomes and in the second case the p arms of the maternal 14 and 15 chromosomes.

Prenatal diagnosis of 30 fetuses at risk for fragile X syndrome.

The results of 30 prenatal diagnoses for fragile X syndrome are reported. Amniotic fluid cells were examined in 1 case, fetal blood in 4, and chorionic villi samples in the others. Of the 5 fetuses analyzed by cytogenetic methods, 1 had showed 4% of fraXq27.3 expression sites and the pregnancy was terminated. For 1 diagnosis, linkage analysis was used: the female fetus turned out to be normal. In 24 fetuses, the direct analysis of the mutation by StB12.3 probe was performed: 6 female and 3 male fetuses were found to carry a full mutation and 1 female fetus was found to carry a premutation. In 3 cases, the diagnoses were verified on fetal blood samples. Several tissues of 2 aborted male fetuses were analyzed for the fragile X mutation. The results are reported and discussed.

An improved method for the detection of Down's syndrome aneuploidy in uncultured amniocytes.

We report a modified method for the rapid detection of aneuploidies directly on human uncultured amniocytes that simplifies and shortens the entire experimental procedure, yielding signals which allow correct diagnosis of trisomy 21 in 97% of cases. The improvement is based on two points: 1) use of cosmid pockets specific for the Down's syndrome minimal region as FISH probes, and 2) a modified protocol for the fixation and preparation of amniocytes.

Autosomal sex reversal and campomelic dysplasia are caused by mutations in and around the SRY-related gene SOX9.

A human autosomal XY sex reversal locus, SRA1, associated with the skeletal malformation syndrome campomelic dysplasia (CMPD1), has been placed at distal 17q. The SOX9 gene, a positional candidate from the chromosomal location and expression pattern reported for mouse Sox9, was isolated and characterized. SOX9 encodes a putative transcription factor structurally related to the testis-determining factor SRY and is expressed in many adult tissues, and in fetal testis and skeletal tissue. Inactivating mutations on one SOX9 allele identified in nontranslocation CMPD1-SRA1 cases point to haploinsufficiency for SOX9 as the cause for both campomelic dysplasia and autosomal XY sex reversal. The 17q breakpoints in three CMPD1 translocation cases map 50 kb or more from SOX9.

[Supravalvular aortic stenosis: clinical and genetic study of a family group]. / Stenosi aortica sopravalvolare: studio clinico e genetico di un'ampia famiglia.

We describe a family with a high frequency of supravalvular aortic stenosis. The family includes 5 generations and 80 subjects (prospective study in 66, on whom physical examination, ECG, M-mode and two-dimensional echocardiogram were performed, and retrospective analysis of available data in 14). This is the largest family group with this disease studied so far. Thirty-six subjects (45%) were found to be affected. On the basis of the echocardiographic image and of the haemodynamic gradient (when available), three different degrees of supravalvular aortic stenosis were identified. The disease was found to be severe in 8 subjects (22%), moderate in 6 (17%), mild in 13 (36%) and undefined in 8 (22%). In 4 cases multiple pulmonary stenoses were associated with supravalvular aortic stenosis, while in one subject multiple pulmonary stenoses were noted in the absence of aortic abnormalities. In the family we studied, the supravalvular aortic stenosis gene is transmitted with a pattern of inheritance consistent with an autosomal dominant trait with variable expressivity and penetrance (penetrance coefficient = 0.86). A high mortality rate in early childhood was observed, while symptoms and ECG abnormalities were not related to the degree of the stenosis. Furthermore, we found a high rate of mitral valve echocardiographic abnormalities, such as mitral prolapse and systolic anterior motion. The absence of Williams dysmorphic somatic features in the many generations as well as in the large number of patients we studied, appears to exclude the coexistence of Williams and Eisenberg's syndromes in the same family group.

Familial supravalvular aortic stenosis: a genetic study.

Supravalvular aortic stenosis (McKusick 18550) is a rare hereditary condition with autosomal dominant transmission. However, the available data have been limited to small family groups which do not allow the definition of the degree of penetrance of the disease. The present study describes a large family with a high frequency of supravalvular aortic stenosis including five generations and 80 subjects, the largest family group with this disease studied so far. The study was carried out prospectively in 66 subjects (clinical examination, ECG, M mode and two dimensional echocardiography). In 14 subjects available data were examined retrospectively. In 10 patients cardiac catheterisation was performed (prospective study in eight). The disease was present in 36 (45%) of the 80 subjects investigated, on the basis of clinical, echocardiographic, and haemodynamic (when available) criteria. The disease was found to be severe in eight cases (22%), moderate in six cases (17%), mild in 13 (36%), and undefined in eight (22%) patients. In one case (3%), multiple pulmonary stenoses were noted in the absence of supravalvular aortic stenosis. Genetic analysis of these data shows, for the first time, the degree of penetrance of the supravalvular aortic stenosis trait (K = 0.86) and confirms that it is transmitted with incomplete penetrance and variable expressivity.