A duplication in the L1CAM gene associated with X-linked hydrocephalus.

Recently, a mutation in the gene for the neural cell adhesion molecule L1CAM, located at chromosome Xq28, was found in a family with X-linked hydrocephalus (HSAS). However, as the L1CAM mutation could only be identified in one HSAS family, it remained unclear whether or not L1CAM was the gene responsible for HSAS. We have conducted a mutation analysis of L1CAM in 25 HSAS families. The mutation reported previously was not found in any of these families. In one family, however, a 1.3 kilobases (kb) genomic duplication was identified, cosegregating with HSAS and significantly changing the intracellular domain of the L1CAM protein. These results confirm that L1CAM is the HSAS gene.

MASA syndrome is due to mutations in the neural cell adhesion gene L1CAM.

MASA syndrome is a recessive X-linked disorder characterized by mental retardation, adducted thumbs, shuffling gait, aphasia and, in some cases, hydrocephalus. Since it has been shown that X-linked hydrocephalus can be caused by mutations in L1CAM, a neuronal cell adhesion molecule, we performed an L1CAM mutation analysis in eight unrelated patients with MASA syndrome. Three different L1CAM mutations were identified: a deletion removing part of the open reading frame and two point mutations resulting in amino acid substitutions. L1CAM, therefore, harbours mutations leading to either MASA syndrome or HSAS, and might be frequently implicated in X-linked mental retardation with or without hydrocephalus.

The full mutation in the FMR-1 gene of male fragile X patients is absent in their sperm.

Fragile X syndrome is characterized at the molecular level by amplification of a (CGG)n repeat and hypermethylation of a CpG island preceeding the open reading frame of the fragile X gene (FMR-1) located in Xq27.3. Anticipation in this syndrome is associated with progressive amplification of the (CGG)n repeat from a premutation to a full mutation through consecutive generations. Remarkably, expansion of the premutation to the full mutation is strictly maternal. To clarify this parental influence we studied FMR-1 in sperm of four male fragile X patients. This showed that only the premutation was present in their sperm, although they had a full mutation in peripheral lymphocytes. This might suggest that expansion of the premutation to the full mutation in FMR-1 does not occur in meiosis but in a postzygotic stage.

A point mutation in the FMR-1 gene associated with fragile X mental retardation.

The vast majority of patients with fragile X syndrome show a folate-sensitive fragile site at Xq27.3 (FRAXA) at the cytogenetic level, and both amplification of the (CGG)n repeat and hypermethylation of the CpG island in the 5' fragile X gene (FMR-1) at the molecular level. We have studied the FMR-1 gene of a patient with the fragile X phenotype but without cytogenetic expression of FRAXA, a (CGG)n repeat of normal length and an unmethylated CpG island. We find a single point mutation in FMR-1 resulting in an lle367Asn substitution. This de novo mutation is absent in the patient's family and in 130 control X chromosomes, suggesting that the mutation causes the clinical abnormalities. Our results suggest that mutations in FMR-1 are directly responsible for fragile X syndrome, irrespective of possible secondary effects caused by FRAXA.

CRASH syndrome: clinical spectrum of corpus callosum hypoplasia, retardation, adducted thumbs, spastic paraparesis and hydrocephalus due to mutations in one single gene, L1.

L1 is a neuronal cell adhesion molecule with important functions in the development of the nervous system. The gene encoding L1 is located near the telomere of the long arm of the X chromosome in Xq28. We review here the evidence that several X-linked mental retardation syndromes including X-linked hydrocephalus (HSAS), MASA syndrome, X-linked complicated spastic paraparesis (SP1) and X-linked corpus callosum agenesis (ACC) are all due to mutations in the L1 gene. The inter- and intrafamilial variability in families with an L1 mutation is very wide, and patients with HSAS, MASA, SP1 and ACC can be present within the same family. Therefore, we propose here to refer to this clinical syndrome with the acronym CRASH, for Corpus callosum hypoplasia, Retardation, Adducted thumbs, Spastic paraplegia and Hydrocephalus.

Linkage of DNA markers at Xq28 to adrenoleukodystrophy and adrenomyeloneuropathy present within the same family.

We present a large kindred that contained patients with either adrenoleukodystrophy (ALD) or adrenomyeloneuropathy (AMN). The pedigree clearly supported the X-linked mode of inheritance of the nonneonatal form of ALD/AMN. Analysis with DNA markers at Xq28 suggested segregation of both ALD and AMN with an identical haplotype. This indicated that nonneonatal ALD and AMN are caused by a mutation in the same gene at Xq28. It showed, furthermore, that phenotypic differences between ALD and AMN are not necessarily the consequence of allelic heterogeneity due to different mutations within the same gene. The maximal lod score for linkage of the ALD/AMN gene and the multiallelic anonymous DNA marker at DXS52 was 3.0 at a recombination fraction of 0.00. This made a prenatal or presymptomatic diagnosis and heterozygote detection by DNA analysis with this marker reliable.

The clinical spectrum of mutations in L1, a neuronal cell adhesion molecule.

Mutations in the gene encoding the neuronal cell adhesion molecule L1 are responsible for several syndromes with clinical overlap, including X-linked hydrocephalus (XLH, HSAS), MASA (mental retardation, aphasias, shuffling gait, adducted thumbs) syndrome, complicated X-linked spastic paraplegia (SP 1), X-linked mental retardation-clasped thumb (MR-CT) syndrome, and some forms of X-linked agenesis of the corpus callosum (ACC). We review 34 L1 mutations in patients with these phenotypes.

CAG repeat contraction in the androgen receptor gene in three brothers with mental retardation.

We report on three brothers with mental retardation and a contracted CAG repeat in the androgen receptor (AR) gene. It is known that expansion of the CAG repeat in this gene leads to spinal and bulbar muscular atrophy (SBMA or Kennedy disease); however, contracted repeats have not yet been implicated in disease. As the range of the length of CAG repeats in the AR gene, like those of other genes associated with dynamic mutations, follows a normal distribution, the theoretical possibility of disease at both ends of the distribution should be considered.

Two brothers with mental retardation discordant for the fragile-X syndrome.

We describe two male sibs with mental retardation discordant for the fragile-X syndrome. In the younger sib, chromosome analysis under folate deprivation showed a fragile site at Xq27.3 in 12-46% of mitoses. In the older sib, however, repeated chromosome analyses (six different cultures with analysis of 50 mitoses each) under identical conditions could not detect any fragile-X site. Using DNA probes linked to the fragile-X gene, we found evidence that the two sibs inherited a different maternal X chromosome at Xq27.3. This excluded the presence of the fragile-X syndrome in the older sib with a probability of greater than 99%.

A case of atresia ani with rectovestibular fistulae in an alpaca (L. pacos).

This communication reviews the generally accepted embryological development of rectovestibular fistulae and describes in detail, the diagnostic procedures and clinical findings of this condition in an alpaca (L. pacos). Specific modalities are detailed which facilitate this diagnosis in an animal with atresia ani. Comments are also directed to the incidence, reporting, and documentation of this and related conditions in South American camelids.

An optimized DHPLC protocol for molecular testing of the EXT1 and EXT2 genes in hereditary multiple osteochondromas.

Hereditary multiple osteochondromas (MO) is an autosomal dominant bone disorder characterized by the presence of bony outgrowths (osteochondromas or exostoses) on the long bones. MO is caused by mutations in the EXT1 or EXT2 genes, which encode glycosyltransferases implicated in heparan sulfate biosynthesis. Standard mutation analysis performed by sequencing analysis of all coding exons of the EXT1 and EXT2 genes reveals a mutation in approximately 80% of the MO patients. We have now optimized and validated a denaturing high-performance liquid chromatography (DHPLC)-based protocol for screening of all EXT1- and EXT2-coding exons in a set of 49 MO patients with an EXT1 or EXT2 mutation. Under the optimized DHPLC conditions, all mutations were detected. These include 20 previously described mutations and 29 new mutations - 20 new EXT1 and nine new EXT2 mutations. The protocol described here, therefore, provides a sensitive and cost-sparing alternative for direct sequencing analysis of the MO-causing genes.

BglII RFLP in DXS 498 between the pigment gene repeat unit, RCP and GCP.

The red (RCP) and green (GCP) color pigment genes are located in Xq28, a chromosomal region implicated in many genetic disorders. The restriction fragment length polymorphism (RFLP) we describe here will be useful for linkage analysis in these disorders.

PCR detection of a BclI RFLP in the G6PD gene of Caucasians.

We have calculated the frequencies of two alleles of the glucose-6-phosphate dehydrogenase gene in a randomly selected group of Caucasians. Allele 1 has a frequency of 82%, whereas that of allele 2 is 18%.

Genotype-phenotype correlation in L1 associated diseases.

The neural cell adhesion molecule L1 (L1CAM) plays a key role during embryonic development of the nervous system and is involved in memory and learning. Mutations in the L1 gene are responsible for four X linked neurological conditions: X linked hydrocephalus (HSAS), MASA syndrome, complicated spastic paraplegia type 1 (SP-1), and X linked agenesis of the corpus callosum. As the clinical picture of these four L1 associated diseases shows considerable overlap and is characterised by Corpus callosum hypoplasia, mental Retardation, Adducted thumbs, Spastic paraplegia, and Hydrocephalus, these conditions have recently been lumped together into the CRASH syndrome. We investigate here whether a genotype-phenotype correlation exists in CRASH syndrome since its clinical spectrum is highly variable and numerous L1 mutations have been described. We found that (1) mutations in the extracellular part of L1 leading to truncation or absence of L1 cause a severe phenotype, (2) mutations in the cytoplasmic domain of L1 give rise to a milder phenotype than extracellular mutations, and (3) extracellular missense mutations affecting amino acids situated on the surface of a domain cause a milder phenotype than those affecting amino acids buried in the core of the domain.

DNA Diagnosis of Cystic Fibrosis by Direct Detection of the Af508 Mutation.

Cystic fibrosis (CF) is one of the most frequent recessive disorders among Caucasians. DNA analysis is perfonned by linkage analysis with DNA markers tightly linked to the CF gene. Cloning and sequencing of the cystic fibrosis gene, however, revealed ti.lat the major disease mutation is a phenylalanine deletion at amino acid position 508 of the mature protein (dF508). These recent discoveries open great perspectives for the diagnosis of cystic fibrosis and for the detection of carriers in the nonnal population. In the present study we have used the polymerase chain reaction to detect the dF508 mutation. This mutation was present on 80.3% of the CF chromosomes in the Belgian population. Twenty-three of 740 nonnal individuals (3, I %) were heterozygous carriers. Therefore, the frequencyofheterozygous carriers in the Belgian population is estimated to be about 3, 9 % or I in every 26 individuals.

L1-associated diseases: clinical geneticists divide, molecular geneticists unite.

The neuronal cell adhesion molecule L1 (L1CAM) is a transmembrane glycoprotein belonging to the immunoglobulin superfamily and is essential in the development of the nervous system. It is mainly expressed on neurons and Schwann cells, and plays a key role in axon outgrowth and pathfinding through interactions with various extracellular ligands and intracellular second messenger systems. Mutations in L1 are responsible for a wide spectrum of neurologic abnormalities and mental retardation. This spectrum includes X-linked hydrocephalus, MASA syndrome, X-linked complicated spastic paraplegia type 1 and X-linked agenesis of the corpus callosum. These four diseases were initially described as distinct clinical entities with an overlapping clinical spectrum, but can now be lumped into one syndrome caused by mutations in the L1 gene. The main clinical features of this spectrum are Corpus callosum hypoplasia, mental Retardation, Adducted thumbs, Spastic paraplegia and Hydrocephalus, which has led to the acronym CRASH syndrome.

Localization of a gene responsible for nonspecific mental retardation (MRX9) to the pericentromeric region of the X chromosome.

Nonspecific X-linked mental retardation (MRX) includes several distinct entities with mental retardation but without additional distinguishing features. The MRX family reported here has been classified previously as MRX9. In this study, we performed linkage analysis of MRX9 with a panel of 43 polymorphic DNA markers dispersed over chromosome X. Two-point linkage analysis revealed lod scores of 3.52 and 3.82 at 0% recombination for OATL1 and MAOA, both located in Xp11.2-p11.4. Lod scores for linkage with PGK1P1, DXS106, and DXS132, all located in Xq11-q13, were 3.83, 3.82, and 3.52, respectively, all at 0% recombination. Multipoint linkage analysis showed two peaks with MAOA and DXS132/DXS106, respectively. Analysis of recombinational events indicated a position of the MRX9 gene between DXS164 and DXS453. These findings are compatible with a location of the MRX9 gene in the pericentromeric region of the X chromosome at Xp21-q13.