Collaborative study of mosaic tetrasomy 12p or Pallister-Killian syndrome (nineteen fetuses or children).

The difficulties in the diagnosis of Pallister-Killian syndrome are illustrated in this study of nineteen fetuses and children. Diagnosis based on clinical appearance alone is often difficult due to the broad spectrum of clinical anomalies not specific to this syndrome. Due to mosaicism, it is altogether necessary to examine several tissues for the presence of tetrasomy 12p, including circulating lymphocytes in which mosaicism can be as low as 1-3%, amniocytes, chorionic cells and skin fibro-blasts in which mosaicism ranges from 6-100%. When highly suspected on ultrasound examination, the diagnosis recommends prenatal cytogenetic studies because survivors are severely mentally retarded. All the cases are sporadic with only a single preliminary report of recurrence. The cytogenetic diagnosis is therefore helpful in order to reassure family members in regard to genetic counseling.

X-linked dominant Charcot-Marie-Tooth neuropathy (CMTX): new mutations in the connexin32 gene.

X-linked dominant Charcot-Marie-Tooth (CMTX) neuropathy has been mapped to the Xq13 region. Subsequently, several mutations that could account for CMTX have been detected in the coding part of the connexin32 (Cx32) gene, which is located within this region. In order to develop more specific diagnostic tools, we have begun a systematic screening of families with dominant CMTX for mutations in the coding region of the Cx32 gene. This report describes a study of ten families and different mutations segregating with the disease were detected in five of them. In addition to the previously reported Arg22stop and Arg215Trp substitutions, three novel mutations are described, including two different missense mutations at codon Arg22 (Arg22Pro and Arg22Gly), and a nonsense mutation at codon Trp133. The identification of new CMTX-causing mutations is a critical step for carrier detection and presymptomatic diagnosis, and should provide essential information on the structure-function relationship of Cx32 in vitro as well as in vivo.

No evidence of genetic heterogeneity in Crouzon craniofacial dysostosis.

Crouzon craniofacial dysostosis (CFD) is an autosomal dominant form of craniosynostosis characterized by an abnormal skull shape, with hypertelorism, prominent eyes and midfacial retrusion. Recently, a gene for CFD has been mapped to chromosome 10q25-q26 and mutations in exon B of the fibroblast growth factor receptor 2 (FGFR2) gene have been identified. Here, we report the mapping of a CFD gene to chromosome 10q by close linkage to probe AFMa197wb1 at locus D10 S1483 in six unrelated families of French ancestry (Zmax = 4.69 at theta = 0) and provide additional evidence of genetic homogeneity of this condition. In addition, we report a novel mutation in exon B of the FGFR2 gene (Cys 342 Trp) in familial CFD and describe recurrent mutations at codon 342 as a particularly frequent event in CFD. Since mutations in the extracellular domain of the FGFR2 gene are observed in a few clinically distinct craniosynostosis syndromes (CFD, Jackson-Weiss, Apert and Pfeiffer), the present study gives support to the variable clinical expression of FGFR2 mutations in humans.

Skewed inactivation of an X chromosome deleted at the dystrophin gene in an asymptomatic mother and her affected daughter.

A girl with severe Becker muscular dystrophy and apparently normal chromosomes had a heterozygous deletion for exons 51, 52, and 53 of the dystrophin gene. This deletion was transmitted by her mother, who was unaffected. To differentiate the normal and the deleted X chromosomes, fluorescence in situ hybridization (FISH) was applied to metaphase chromosomes, using probes for both exons 51 and 52, which are only 388 and 113 base pairs long, respectively. FISH signals were observed in one or both chromatids of one chromosome, but never on both chromosomes, suggesting the lack of hybridization on the deleted X chromosome. Using 5-bromodeoxyuridine incorporation to differentiate the late (inactive) and the early replicating (active) X chromosomes, 77% of the signals were observed on the active X chromosomes in the mother. This percentage was only 18% in the daughter, suggesting that skewed inactivation of the X chromosomes was responsible for the phenotypic differences.

A gene for Holt-Oram syndrome maps to the distal long arm of chromosome 12.

Holt-Oram syndrome (HOS) is an autosomal dominant condition of unknown origin characterized by congenital septal heart defects with associated malformations of the upper limbs (radial ray). Here, we report on the mapping of a gene causing HOS to the distal long arm of chromosome 12 (12q21-qter) by linkage analysis in nine informative families (Zmax = 6.81 at theta = 0 at the D12S354 locus). Also, multipoint linkage analysis places the HOS gene within the genetic interval between D12S84 and D12S79 (multipoint lod-score in log base 10 = 8.10). The mapping of a gene for HOS is, to our knowledge, the first chromosomal localization of a gene responsible for congenital septal heart defect in human. The characterization of the HOS gene will hopefully shed light on the molecular mechanisms that govern heart septation in the early stages of embryogenesis.

A somatic origin of homologous Robertsonian translocations and isochromosomes.

One t(14q14q), three t(15q15q), two t(21q21q), and two t(22q22q) nonmosaic, apparently balanced, de novo Robertsonian translocation cases were investigated with polymorphic markers to establish the origin of the translocated chromosomes. Four cases had results indicative of an isochromosome: one t(14q14q) case with mild mental retardation and maternal uniparental disomy (UPD) for chromosome 14, one t(15q15q) case with the Prader-Willi syndrome and UPD(15), a phenotypically normal carrier of t(22q22q) with maternal UPD(22), and a phenotypically normal t(21q21q) case of paternal UPD(21). All UPD cases showed complete homozygosity throughout the involved chromosome, which is supportive of a postmeiotic origin. In the remaining four cases, maternal and paternal inheritance of the involved chromosome was found, which unambiguously implies a somatic origin. One t(15q15q) female had a child with a ring chromosome 15, which was also of probable postmeiotic origin as recombination between grandparental haplotypes had occurred prior to ring formation. UPD might be expected to result from de novo Robertsonian translocations of meiotic origin; however, all de novo homologous translocation cases, so far reported, with UPD of chromosomes 14, 15, 21, or 22 have been isochromosomes. These data provide the first direct evidence that nonmosaic Robertsonian translocations, as well as isochromosomes, are commonly the result of a mitotic exchange.

Split hand/split foot deformity and LADD syndrome in a family: overlap between the EEC and LADD syndromes.

A mother and daughter are reported with apparently dissimilar syndromes. The mother has a split hand/split foot deformity and the daughter a condition consistent with a diagnosis of LADD syndrome. Absence of clefting and deficient formation of saliva and tears are the main signs that differentiate the LADD from the EEC syndrome. However, no distinct feature is constant between these two autosomal dominant disorders that show great phenotypic variability. This report emphasises the overlap between the LADD and the EEC syndromes.

Prenatal exclusion of X-linked hydrocephalus-stenosis of the aqueduct of Sylvius sequence using closely linked DNA markers.

X-linked hydrocephalus-stenosis of the aqueduct of Sylvius sequence (H-SAS, MIM number 307,000) is a rare genetic disorder characterized by hydrocephalus, macrocephaly, adducted thumbs, spasticity, mental retardation, and cerebral malformations. This regularly lethal condition is usually diagnosed at birth or prenatally by ultrasound, but hydrocephalus may be moderate or even undetectable on fetal ultrasound examination. Moreover, since heterozygous women are asymptomatic, carrier detection is at present impossible before the birth of an affected son. Therefore, mapping the H-SAS locus to distal Xq (Xq28) was of primary importance for genetic counselling and prenatal diagnosis. Here, we report prenatal exclusion of H-SAS with a probability of 97.6 per cent in two male fetuses with a 50 per cent a priori risk of being affected using closely linked Xq28 DNA markers.

[Coffin-Lowry syndrome and hyperprolinemia]. / Syndrome de Coffin-Lowry et hyperprolinémie.

BACKGROUND: The main features of the Coffin-Lowry syndrome are mental retardation and features of a peculiar pugilistic nose, large ears, tapered fingers, drumstick terminal phalanges by X-rays and kyphoscoliosis. Inheritance is probably X-linked dominant. Its early diagnosis is difficult. CASE REPORT: A 31 month-old boy was admitted for mental retardation. His weight and height were normal, but his facies showed telecanthus, anteverted nares and a prominent frontal region. His hands appeared puffy with bulbous tapering fingers. Amino-acid chromatography showed hyperprolinemia (732 mumol/l) plus iminoglycinuria. His mother had a short stature, mental retardation and similar, although minor, manifestations of the Coffin-Lowry syndrome in her face, hands and fingers. She had moderate hyperprolinemia (391 mumol/l) without hyperglycinuria. The patient's father showed no physical abnormalities, but he also had hyperprolinemia (671 mumol/l) and hyperglycinuria. CONCLUSION: The association of the Coffin-Lowry syndrome and hyperprolinemia in this family seems fortuitous.

Townes-Brocks syndrome in an infant with translocation t (5;16).

We report the occurrence of Townes-Brocks syndrome (TBS) in an infant with a two break reciprocal translocation between chromosome 5 and chromosome 16. The occurrence of both abnormalities in the same subject could be due to chance. However, it is of interest to note that a familial case of TBS associated with an inv(16) with the same breakpoint at 16q12.1 has been reported. We suggest the possible disruption of the TBS gene at this breakpoint.

The gene for X-linked hydrocephalus maps to Xq28, distal to DXS52.

We report the study of five independent X-linked hydrocephalus (HSAS1) families with polymorphic DNA markers of the Xq28 region. A total of 58 individuals, including 7 living affected males and 22 obligate carriers, have been studied. Maximum lod score was 7.21 at theta = 2.40% for DXS52 (St14-1). A single recombination event was observed between this marker and the HSAS1 locus. Other markers studied were DXS296 (Z = 2.02 at theta = 2.5%), DXS304 (Z = 4.37 at theta = 7.8%), DXS74 (Z = 3.50 at theta = 0%), DXS15 (Z = 1.96 at theta = 5.7%), DXS134 (Z = 3.31 at theta = 0%), and F8C (Z = 5.79 at theta = 0%). These data confirm the localization of the HSAS1 gene to Xq28 and provide evidence for genetic homogeneity of this syndrome. In addition, examination of two obligate recombinant meioses along with multipoint linkage analysis supports the distal localization of the HSAS1 locus with respect to the DXS52 cluster. These observations are of potential interest for future studies aimed at HSAS1 gene characterization.

X-linked hydrocephalus: clinical heterogeneity at a single gene locus.

X-linked hydrocephalus-stenosis of the aqueduct of Sylvius sequence (H-SAS, MIM number 30007) is a rare genetic disorder characterized by hydrocephalus, macrocephaly, adducted thumbs, spasticity, agenesis of corpus callosum and mental retardation. We confirm here the localisation of the mutant gene on Xq (Xq 2.8) by linkage analysis in a 5-generation pedigree (maximum lod score of Z = 4.57 at theta = 0.04 with probe St14 at locus DXS52) and emphasise the phenotypic variability of the disease. Ventricular dilatation in affected males was either severe and diagnosed antenatally or moderate and consistent with a long survival with little or no macrocephaly. Since other X-linked syndromes of mental retardation with spasticity and flexion deformities of the thumbs have previously been shown to map to the Xq 2.8 region as well (e.g. MASA syndrome and spastic paraplegia), the present results raise the question of whether H-SAS syndrome, MASA syndrome and spastic paraplegia with mental retardation might represent different phenotypic expression of various mutations at the same locus.

Moderate instability of the trinucleotide repeat in spino bulbar muscular atrophy.

Increased length of a protein-coding CAG repeat within the androgen receptor gene appears to be the only type of mutation responsible for spino-bulbal muscular atrophy (SBMA or Kennedy disease). We have analysed a large 4-generation SBMA family and found that the mutant allele was unstable upon transmission from parent to child, with a documented variation from 46 to 53 repeats and a tendency to increase in size (7 increases and a single decrease in 17 events), which appeared stronger upon transmission from a male than from a female. Our results suggest also limited somatic instability of the abnormal allele, with observable variation of up to 2-3 repeats. This indicates that the behavior of the CAG repeat is similar to that observed for small premutations in the fragile X syndrome, or small abnormal alleles in myotonic dystrophy, two diseases which are caused by expansion of an unstable trinucleotide repeat.

Idiopathic arterial calcification in a stillborn complicated by pleural hemorrhage and hydrops fetalis.

We report a case of idiopathic arterial calcification in a stillborn. As usually noted in this rare entity, the pregnancy was complicated by a polyhydramnios. The postmortem examination showed generalized arterial calcification, periarticular calcific deposits, and a large pleural hemorrhage. The causes of fetal hydrops in idiopathic infantile calcification are discussed, and, in the present case, the absence of myocardial ischemic lesion suggests that the fetal hydrops and the fetal death could have been caused by the bulky blood clot that was present in the right pleural cavity. The pathogenesis remains undetermined, but a primitive inherent defect of the elastic elements seems to initiate this disorder.

[Cystic adenomatoid malformation of the lung, bilateral renal agenesis and left heart hypoplasia. An unusual association in Potter's syndrome]. / Malformation adénomatoïde kystique du poumon, agénésie rénale bilatérale et hypoplasie du coeur gauche. Une association inhabituelle dans un syndrome de Potter.

We describe an autopsy case of congenital cystic adenomatoid malformation of the lung (CCAM) associated with bilateral renal agenesis. Prenatal ultrasound examination showed additional left heart hypoplastic syndrome. A therapeutic abortion was induced at 23 weeks of gestation. The association CCAM-bilateral renal agenesis is a rare condition (5 cases previously described) which has to be known because of the mitigation effect of the CCAM on the oligohydramnios determined by bilateral renal agenesis. However, this instance is usually associated with oligohydramnios. The pathogenesis of polyhydramnios in isolated CCAM is discussed in regard with these data.

[Fetus in fetu and acardiac monster: can the similar patterns of these 2 malformations be explained by a common morphogenic mechanism?]. / Foetus in fetu et monstre acardiaque: un mécanisme morphogénique commun explique-t-il les similitudes de ces deux malformations?

Fetus in fetu and acardiac monster are two unusual malformations (estimated incidences: 1 in 500,000 and 1 in 34,600 deliveries respectively) which present very similar morphological patterns. The authors report two cases of acardiac monster and a case of fetus in fetu which emphasize this fact. These findings suggest that a single morphogenic mechanism leads to the defects observed in these two groups of malformations.