Recurrent rearrangements of chromosome 1q21.1 and variable pediatric phenotypes

BACKGROUND

Duplications and deletions in the human genome can cause disease or predispose persons to disease. Advances in technologies to detect these changes allow for the routine identification of submicroscopic imbalances in large numbers of patients.

METHODS

We tested for the presence of microdeletions and microduplications at a specific region of chromosome 1q21.1 in two groups of patients with unexplained mental retardation, autism, or congenital anomalies and in unaffected persons.

RESULTS

We identified 25 persons with a recurrent 1.35-Mb deletion within 1q21.1 from screening 5218 patients. The microdeletions had arisen de novo in eight patients, were inherited from a mildly affected parent in three patients, were inherited from an apparently unaffected parent in six patients, and were of unknown inheritance in eight patients. The deletion was absent in a series of 4737 control persons (P=1.1x10(-7)). We found considerable variability in the level of phenotypic expression of the microdeletion; phenotypes included mild-to-moderate mental retardation, microcephaly, cardiac abnormalities, and cataracts. The reciprocal duplication was enriched in nine children with mental retardation or autism spectrum disorder and other variable features (P=0.02). We identified three deletions and three duplications of the 1q21.1 region in an independent sample of 788 patients with mental retardation and congenital anomalies.

CONCLUSIONS

We have identified recurrent molecular lesions that elude syndromic classification and whose disease manifestations must be considered in a broader context of development as opposed to being assigned to a specific disease. Clinical diagnosis in patients with these lesions may be most readily achieved on the basis of genotype rather than phenotype.

A systematic, large-scale resequencing screen of X-chromosome coding exons in mental retardation

Large-scale systematic resequencing has been proposed as the key future strategy for the discovery of rare, disease-causing sequence variants across the spectrum of human complex disease. We have sequenced the coding exons of the X chromosome in 208 families with X-linked mental retardation (XLMR), the largest direct screen for constitutional disease-causing mutations thus far reported. The screen has discovered nine genes implicated in XLMR, including SYP, ZNF711 and CASK reported here, confirming the power of this strategy. The study has, however, also highlighted issues confronting whole-genome sequencing screens, including the observation that loss of function of 1% or more of X-chromosome genes is compatible with apparently normal existence.

A recurrent 15q13.3 microdeletion syndrome associated with mental retardation and seizures

We report a recurrent microdeletion syndrome causing mental retardation, epilepsy and variable facial and digital dysmorphisms. We describe nine affected individuals, including six probands: two with de novo deletions, two who inherited the deletion from an affected parent and two with unknown inheritance. The proximal breakpoint of the largest deletion is contiguous with breakpoint 3 (BP3) of the Prader-Willi and Angelman syndrome region, extending 3.95 Mb distally to BP5. A smaller 1.5-Mb deletion has a proximal breakpoint within the larger deletion (BP4) and shares the same distal BP5. This recurrent 1.5-Mb deletion contains six genes, including a candidate gene for epilepsy (CHRNA7) that is probably responsible for the observed seizure phenotype. The BP4-BP5 region undergoes frequent inversion, suggesting a possible link between this inversion polymorphism and recurrent deletion. The frequency of these microdeletions in mental retardation cases is approximately 0.3% (6/2,082 tested), a prevalence comparable to that of Williams, Angelman and Prader-Willi syndromes.

Allan-Herndon-Dudley syndrome and the monocarboxylate transporter 8 (MCT8) gene

Allan-Herndon-Dudley syndrome was among the first of the X-linked mental retardation syndromes to be described (in 1944) and among the first to be regionally mapped on the X chromosome (in 1990). Six large families with the syndrome have been identified, and linkage studies have placed the gene locus in Xq13.2. Mutations in the monocarboxylate transporter 8 gene (MCT8) have been found in each of the six families. One essential function of the protein encoded by this gene appears to be the transport of triiodothyronine into neurons. Abnormal transporter function is reflected in elevated free triiodothyronine and lowered free thyroxine levels in the blood. Infancy and childhood in the Allan-Herndon-Dudley syndrome are marked by hypotonia, weakness, reduced muscle mass, and delay of developmental milestones. Facial manifestations are not distinctive, but the face tends to be elongated with bifrontal narrowing, and the ears are often simply formed or cupped. Some patients have myopathic facies. Generalized weakness is manifested by excessive drooling, forward positioning of the head and neck, failure to ambulate independently, or ataxia in those who do ambulate. Speech is dysarthric or absent altogether. Hypotonia gives way in adult life to spasticity. The hands exhibit dystonic and athetoid posturing and fisting. Cognitive development is severely impaired. No major malformations occur, intrauterine growth is not impaired, and head circumference and genital development are usually normal. Behavior tends to be passive, with little evidence of aggressive or disruptive behavior. Although clinical signs of thyroid dysfunction are usually absent in affected males, the disturbances in blood levels of thyroid hormones suggest the possibility of systematic detection through screening of high-risk populations.

Autism and maternally derived aberrations of chromosome 15q

Of the chronic mental disabilities of childhood, autism is causally least well understood. The former view that autism was rooted in exposure to humorless and perfectionistic parenting has given way to the notion that genetic influences are dominant underlying factors. Still, identification of specific heritable factors has been slow with causes identified in only a few cases in unselected series. A broad search for genetic and environmental influences that cause or predispose to autism is the major thrust of the South Carolina Autism Project. Among the first 100 cases enrolled in the project, abnormalities of chromosome 15 have emerged as the single most common cause. The four abnormalities identified include deletions and duplications of proximal 15q. Other chromosome aberrations seen in single cases include a balanced 13;16 translocation, a pericentric inversion 12, a deletion of 20p, and a ring 7. Candidate genes involved in the 15q region affected by duplication and deletion include the ubiquitin-protein ligase (UBE3A) gene responsible for Angelman syndrome and genes for three GABA(A) receptor subunits. In all cases, the deletions or duplications occurred on the chromosome inherited from the mother.

Isolation and characterization of the faciogenital dysplasia (Aarskog-Scott syndrome) gene: a putative Rho/Rac guanine nucleotide exchange factor

Faciogenital dysplasia (FGDY), also known as Aarskog-Scott syndrome, is an X-linked developmental disorder characterized by disproportionately short stature and by facial, skeletal, and urogenital anomalies. Molecular genetic analyses mapped FGDY to chromosome Xp11.21. To clone this gene, YAC clones spanning an FGDY-specific translocation breakpoint were isolated. An isolated cDNA, FGD1, is disrupted by the breakpoint, and FGD1 mutations cosegregate with the disease. FGD1 codes for a 961 amino acid protein that has strong homology to Rho/Rac guanine nucleotide exchange factors (GEFs), contains a cysteine-rich zinc finger-like region, and, like the RasGEF mSos, contains two potential SH3-binding sites. These results provide compelling evidence that FGD1 is responsible for FGDY and suggest that FGD1 is a Rho/RacGEF involved in mammalian development.

Evaluation of mental retardation: recommendations of a Consensus Conference: American College of Medical Genetics

A Consensus Conference utilizing available literature and expert opinion sponsored by the American College of Medical Genetics in October 1995 evaluated the rational approach to the individual with mental retardation. Although no uniform protocol replaces individual clinician judgement, the consensus recommendations were as follows: 1. The individual with mental retardation, the family, and medical care providers benefit from a focused clinical and laboratory evaluation aimed at establishing causation and in providing counseling, prognosis, recurrence risks, and guidelines for management. 2. Essential elements of the evaluation include a three-generation pedigree: pre-, peri-, and post-natal history, complete physical examination focused on the presence of minor anomalies, neurologic examination, and assessment of the behavioral phenotype. 3. Selective laboratory testing should, in most patients, include a banded karyotype. Fragile X testing should be strongly considered in both males and females with unexplained mental retardation, especially in the presence of a positive family history, a consistent physical and behavioral phenotype and absence of major structural abnormalities. Metabolic testing should be initialed in the presence of suggestive clinical and physical findings. Neuroimaging should be considered in patients without a known diagnosis especially in the presence of neurologic symptoms, cranial contour abnormalities, microcephaly, or macrocephaly. In most situations MRI is the testing modality of choice. 4. Sequential evaluation of the patient, occasionally over several years, is often necessary for diagnosis, allowing for delineation of the physical and behavioral phenotype, a logical approach to ancillary testing and appropriate prognostic and reproductive counseling.

Mutations in UPF3B, a member of the nonsense-mediated mRNA decay complex, cause syndromic and nonsyndromic mental retardation

Nonsense-mediated mRNA decay (NMD) is of universal biological significance. It has emerged as an important global RNA, DNA and translation regulatory pathway. By systematically sequencing 737 genes (annotated in the Vertebrate Genome Annotation database) on the human X chromosome in 250 families with X-linked mental retardation, we identified mutations in the UPF3 regulator of nonsense transcripts homolog B (yeast) (UPF3B) leading to protein truncations in three families: two with the Lujan-Fryns phenotype and one with the FG phenotype. We also identified a missense mutation in another family with nonsyndromic mental retardation. Three mutations lead to the introduction of a premature termination codon and subsequent NMD of mutant UPF3B mRNA. Protein blot analysis using lymphoblastoid cell lines from affected individuals showed an absence of the UPF3B protein in two families. The UPF3B protein is an important component of the NMD surveillance machinery. Our results directly implicate abnormalities of NMD in human disease and suggest at least partial redundancy of NMD pathways.

Evaluation of DNA Methylation Episignatures for Diagnosis and Phenotype Correlations in 42 Mendelian Neurodevelopmental Disorders

Genetic syndromes frequently present with overlapping clinical features and inconclusive or ambiguous genetic findings which can confound accurate diagnosis and clinical management. An expanding number of genetic syndromes have been shown to have unique genomic DNA methylation patterns (called "episignatures"). Peripheral blood episignatures can be used for diagnostic testing as well as for the interpretation of ambiguous genetic test results. We present here an approach to episignature mapping in 42 genetic syndromes, which has allowed the identification of 34 robust disease-specific episignatures. We examine emerging patterns of overlap, as well as similarities and hierarchical relationships across these episignatures, to highlight their key features as they are related to genetic heterogeneity, dosage effect, unaffected carrier status, and incomplete penetrance. We demonstrate the necessity of multiclass modeling for accurate genetic variant classification and show how disease classification using a single episignature at a time can sometimes lead to classification errors in closely related episignatures. We demonstrate the utility of this tool in resolving ambiguous clinical cases and identification of previously undiagnosed cases through mass screening of a large cohort of subjects with developmental delays and congenital anomalies. This study more than doubles the number of published syndromes with DNA methylation episignatures and, most significantly, opens new avenues for accurate diagnosis and clinical assessment in individuals affected by these disorders.

Mutations in CUL4B, which encodes a ubiquitin E3 ligase subunit, cause an X-linked mental retardation syndrome associated with aggressive outbursts, seizures, relative macrocephaly, central obesity, hypogonadism, pes cavus, and tremor

We have identified three truncating, two splice-site, and three missense variants at conserved amino acids in the CUL4B gene on Xq24 in 8 of 250 families with X-linked mental retardation (XLMR). During affected subjects' adolescence, a syndrome emerged with delayed puberty, hypogonadism, relative macrocephaly, moderate short stature, central obesity, unprovoked aggressive outbursts, fine intention tremor, pes cavus, and abnormalities of the toes. This syndrome was first described by Cazebas et al., in a family that was included in our study and that carried a CUL4B missense variant. CUL4B is a ubiquitin E3 ligase subunit implicated in the regulation of several biological processes, and CUL4B is the first XLMR gene that encodes an E3 ubiquitin ligase. The relatively high frequency of CUL4B mutations in this series indicates that it is one of the most commonly mutated genes underlying XLMR and suggests that its introduction into clinical diagnostics should be a high priority.

Prevalence of SHANK3 variants in patients with different subtypes of autism spectrum disorders

Autism spectrum disorders (ASDs) include three main conditions: autistic disorder (AD), pervasive developmental disorder, not otherwise specified (PDD-NOS), and Asperger syndrome. It has been shown that many genes associated with ASDs are involved in the neuroligin-neurexin interaction at the glutamate synapse: NLGN3, NLGN4, NRXN1, CNTNAP2, and SHANK3. We screened this last gene in two cohorts of ASD patients (133 patients from US and 88 from Italy). We found 5/221 (2.3%) cases with pathogenic alterations: a 106 kb deletion encompassing the SHANK3 gene, two frameshift mutations leading to premature stop codons, a missense mutation (p.Pro141Ala), and a splicing mutation (c.1820-4 G>A). Additionally, in 17 patients (7.7%) we detected a c.1304+48C>T transition affecting a methylated cytosine in a CpG island. This variant is reported as SNP rs76224556 and was found in both US and Italian controls, but it results significantly more frequent in our cases than in the control cohorts. The variant is also significantly more common among PDD-NOS cases than in AD cases. We also screened this gene in an independent replication cohort of 104 US patients with ASDs, in which we found a missense mutation (p.Ala1468Ser) in 1 patient (0.9%), and in 8 patients (7.7%) we detected the c.1304+48C>T transition. While SHANK3 variants are present in any ASD subtype, the SNP rs76224556 appears to be significantly associated with PDD-NOS cases. This represents the first evidence of a genotype-phenotype correlation in ASDs and highlights the importance of a detailed clinical-neuropsychiatric evaluation for the effective genetic screening of ASD patients.

Fragile X and X-linked intellectual disability: four decades of discovery

X-Linked intellectual disability (XLID) accounts for 5%-10% of intellectual disability in males. Over 150 syndromes, the most common of which is the fragile X syndrome, have been described. A large number of families with nonsyndromal XLID, 95 of which have been regionally mapped, have been described as well. Mutations in 102 X-linked genes have been associated with 81 of these XLID syndromes and with 35 of the regionally mapped families with nonsyndromal XLID. Identification of these genes has enabled considerable reclassification and better understanding of the biological basis of XLID. At the same time, it has improved the clinical diagnosis of XLID and allowed for carrier detection and prevention strategies through gamete donation, prenatal diagnosis, and genetic counseling. Progress in delineating XLID has far outpaced the efforts to understand the genetic basis for autosomal intellectual disability. In large measure, this has been because of the relative ease of identifying families with XLID and finding the responsible mutations, as well as the determined and interactive efforts of a small group of researchers worldwide.

5,10 Methylenetetrahydrofolate reductase genetic polymorphism as a risk factor for neural tube defects

Persons with a thermolabile form of the enzyme 5,10 methylenetetrahydrofolate reductase (MTHFR) have reduced enzyme activity and increased plasma homocysteine which can be lowered by supplemental folic acid. Thermolability of the enzyme has recently been shown to be caused by a common mutation (677C-->T) in the MTHFR gene. We studied 41 fibroblast cultures from NTD-affected fetuses and compared their genotypes with those of 109 blood specimens from individuals in the general population. 677C-->T homozygosity was associated with a 7.2 fold increased risk for NTDs (95% confidence interval: 1.8-30.3; p value: 0.001). These preliminary data suggest that the 677C-->T polymorphism of the MTHFR gene is a risk factor for spina bifida and anencephaly that may provide a partial biologic explanation for why folic acid prevents these types of NTD.

A recurrent mutation in MED12 leading to R961W causes Opitz-Kaveggia syndrome

Opitz-Kaveggia syndrome (also known as FG syndrome) is an X-linked disorder characterized by mental retardation, relative macrocephaly, hypotonia and constipation. We report here that the original family for whom the condition is named and five other families have a recurrent mutation (2881C>T, leading to R961W) in MED12 (also called TRAP230 or HOPA), a gene located at Xq13 that functions as a thyroid receptor-associated protein in the Mediator complex.

Recurrent infections, hypotonia, and mental retardation caused by duplication of MECP2 and adjacent region in Xq28

OBJECTIVE

Our goal was to describe the neurologic and clinical features of affected males from families with X-linked patterns of severe mental retardation, hypotonia, recurrent respiratory infection, and microduplication of Xq28 that consistently includes the MECP2 (methyl-CpG binding protein 2) gene.

STUDY DESIGN

To identify duplications, multiplex ligation-dependent probe amplification of the MECP2 gene was performed on male probands from families with X-linked mental retardation. The males either had linkage to Xq28 or had a phenotype consistent with previous reports involving Xq28 functional disomy. After detection of a duplication of MECP2, additional family members were tested to confirm the MECP2 duplication segregated with the affected phenotype, and X-inactivation studies were performed on carrier females.

RESULTS

Six families with multiple affected males having MECP2 duplications were identified by multiplex ligation-dependent probe amplification, and the carrier mothers were subsequently shown to have highly skewed X inactivation. In 5 of 6 families, the microduplication extended proximally to include the L1 cell adhesion molecule gene. The primary clinical features associated with this microduplication are infantile hypotonia, recurrent respiratory infection, severe mental retardation, absence of speech development, seizures, and spasticity.

CONCLUSIONS

Although many of the phenotypic features of our patients are rather nonspecific in cohorts of individuals with syndromic and nonsyndromic mental retardation, the proneness to infection is quite striking because the patients had normal growth and were not physically debilitated. Although the etiology of the infections is not understood, we recommend considering MECP2 dosage studies and a genetics referral in individuals with severe developmental delay and neurologic findings, especially when a history of recurrent respiratory ailments has been documented.

Mutations in the planar cell polarity genes CELSR1 and SCRIB are associated with the severe neural tube defect craniorachischisis

Craniorachischisis (CRN) is a severe neural tube defect (NTD) resulting from failure to initiate closure, leaving the hindbrain and spinal neural tube entirely open. Clues to the genetic basis of this condition come from several mouse models, which harbor mutations in core members of the planar cell polarity (PCP) signaling pathway. Previous studies of humans with CRN failed to identify mutations in the core PCP genes, VANGL1 and VANGL2. Here, we analyzed other key PCP genes: CELSR1, PRICKLE1, PTK7, and SCRIB, with the finding of eight potentially causative mutations in both CELSR1 and SCRIB. Functional effects of these unique or rare human variants were evaluated using known protein-protein interactions as well as subcellular protein localization. While protein interactions were not affected, variants from five of the 36 patients exhibited a profound alteration in subcellular protein localization, with diminution or abolition of trafficking to the plasma membrane. Comparable effects were seen in the crash and spin cycle mouse Celsr1 mutants, and the line-90 mouse Scrib mutant. We conclude that missense variants in CELSR1 and SCRIB may represent a cause of CRN in humans, as in mice, with defective PCP protein trafficking to the plasma membrane a likely pathogenic mechanism.

A unique exonic splice enhancer mutation in a family with X-linked mental retardation and epilepsy points to a novel role of the renin receptor

The renin-angiotensin system (RAS) is essential for blood pressure control and water-electrolyte balance. Until the discovery of the renin receptor, renin was believed to be mainly a circulating enzyme with a unique function, the cleavage of angiotensinogen. We report a unique mutation in the renin receptor gene (ATP6AP2) present in patients with X-linked mental retardation and epilepsy (OMIM no. 300423), but absent in 1200 control X-chromosomes. A silent mutation (c.321C>T, p.D107D) residing in a putative exonic splicing enhancer site resulted in inefficient inclusion of exon 4 in 50% of renin receptor mRNA, as demonstrated by quantitative RT-PCR. Analysis of membrane associated-receptor molecular forms showed the presence of full-length and truncated proteins in the patient. Functional analysis demonstrated that the mutated receptor could bind renin and increase renin catalytic activity, similar to the wild-type receptor, but resulted in a modest and reproducible impairment of ERK1/2 activation. Thus, our findings confirm the importance of the RAS in cognitive processes and indicate a novel specific role for the renin receptor in cognitive functions and brain development.

A new X linked recessive deafness syndrome with blindness, dystonia, fractures, and mental deficiency is linked to Xq22

X linked recessive deafness accounts for only 1.7% of all childhood deafness. Only a few of the at least 28 different X linked syndromes associated with hearing impairment have been characterised at the molecular level. In 1960, a large Norwegian family was reported with early onset progressive sensorineural deafness, which was indexed in McKusick as DFN-1, McKusick 304700. No associated symptoms were described at that time. This family has been restudied clinically. Extensive neurological, neurophysiological, neuroradiological, and biochemical, as well as molecular techniques, have been applied to characterise the X linked recessive syndrome. The family history and extensive characterisation of 16 affected males in five generations confirmed the X linked recessive inheritance and the postlingual progressive nature of the sensorineural deafness. Some obligate carrier females showed signs of minor neuropathy and mild hearing impairment. Restudy of the original DFN-1 family showed that the deafness is part of a progressive X linked recessive syndrome, which includes visual disability leading to cortical blindness, dystonia, fractures, and mental deficiency. Linkage analysis indicated that the gene was linked to locus DXS101 in Xq22 with a lod score of 5.37 (zero recombination). Based on lod-1 support interval of the multipoint analysis, the gene is located in a region spanning from 5 cM proximal to 3 cM distal to this locus. As the proteolipid protein gene (PLP) is within this region and mutations have been shown to be associated with non-classical PMD (Pelizaeus-Merzbacher disease), such as complex X linked hereditary spastic paraplegia, PLP may represent a candidate gene for this disorder. This family represents a new syndrome (Mohr-Tranebjaerg syndrome, MTS) and provides significant new information about a new X linked recessive sydromic type of deafness which was previously thought to be isolated deafness.

Menkes disease: a biochemical abnormality in cultured human fibroblasts

Cultured skin fibroblasts from patients with Menkes disease, an X-linked disorder involving a defect in copper metabolism, were analyzed for copper concentration by means of atomic absorption spectrophotometry. These cultures consistently exhibited elevated copper concentrations (mean = 335.5 ng of copper per mg of protein) when compared to control fibroblast cultures (mean = 59.2 ng of copper per mg of protein). External factors that could influence the copper content of cultures were found not to affect the differences in copper concentration between control and Menkes cells. Furthermore, Menkes cells could be differentiated from cultured fibroblasts of controls, of presumed heterozygotes, and of Wilson's disease patients by copper concentration. These observations led to the conclusion that the increased copper content of cultured Menkes cells was characteristic of Menkes disease, resulting from the expression of the genetic abnormality. This provides a genetic marker, a defect in metal metabolism demonstrated in human fibroblasts, that should prove valuable in both the diagnosis of Menkes disease and in the study of the fundamental defect of this genetic disorder.

Adverse birth outcome among mothers with low serum cholesterol

OBJECTIVE

The objective of this study was to assess whether low maternal serum cholesterol during pregnancy is associated with preterm delivery, impaired fetal growth, or congenital anomalies in women without identified major risk factors for adverse pregnancy outcome.

METHODS

Mother-infant pairs were retrospectively ascertained from among a cohort of 9938 women who were referred to South Carolina prenatal clinics for routine second-trimester serum screening. Banked sera were assayed for total cholesterol; <10th percentile of assayed values (159 mg/dL at mean gestational age of 17.6 weeks) defined a "low total cholesterol" prenatal risk category. Eligible women were aged 21 to 34 years and nonsmoking and did not have diabetes; neonates were liveborn after singleton gestations. Total cholesterol values of eligible mothers were adjusted for gestational age at screening before risk group assignment. The study population included 118 women with low total cholesterol and 940 women with higher total cholesterol. Primary analyses used multivariate regression models to compare rates of preterm delivery, fetal growth parameters, and congenital anomalies between women with low total cholesterol and control subjects with mid-total cholesterol values >10th percentile but <90th percentile.

RESULTS

Prevalence of preterm delivery among mothers with low total cholesterol was 12.7%, compared with 5.0% among control subjects with mid-total cholesterol. The association of low maternal serum cholesterol with preterm birth was observed only among white mothers. Term infants of mothers with low total cholesterol weighed on average 150 g less than those who were born to control mothers. A trend of increased microcephaly risk among neonates of mothers with low total cholesterol was found. Low maternal serum cholesterol was unassociated with risk for congenital anomalies.

CONCLUSIONS

Total serum cholesterol <10th population percentile was strongly associated with preterm delivery among otherwise low-risk white mothers in this pilot study population. Term infants of mothers with low total cholesterol weighed less than control infants among both racial groups.

The original Lujan syndrome family has a novel missense mutation (p.N1007S) in the MED12 gene

A novel missense mutation in the mediator of RNA polymerase II transcription subunit 12 (MED12) gene has been found in the original family with Lujan syndrome and in a second family (K9359) that was initially considered to have Opitz-Kaveggia (FG) syndrome. A different missense mutation in the MED12 gene has been reported previously in the original family with FG syndrome and in five other families with compatible clinical findings. Neither sequence alteration has been found in over 1400 control X chromosomes. Lujan (Lujan-Fryns) syndrome is characterised by tall stature with asthenic habitus, macrocephaly, a tall narrow face, maxillary hypoplasia, a high narrow palate with dental crowding, a small or receding chin, long hands with hyperextensible digits, hypernasal speech, hypotonia, mild-to-moderate mental retardation, behavioural aberrations and dysgenesis of the corpus callosum. Although Lujan syndrome has not been previously considered to be in the differential diagnosis of FG syndrome, there are some overlapping clinical manifestations. Specifically, these are dysgenesis of the corpus callosum, macrocephaly/relative macrocephaly, a tall forehead, hypotonia, mental retardation and behavioural disturbances. Thus, it seems that these two X-linked mental retardation syndromes are allelic, with mutations in the MED12 gene.

Obstetrical and gynecological complications in fragile X carriers: a multicenter study

We have conducted a multicenter obstetrical and gynecological survey of women in fragile X families. Included in the study were 131 gene carriers (39 with a full mutation and 92 with a premutation) and 109 noncarriers. Analysis indicated that higher numbers of fragile X gene carriers reported having irregular menses and other gynecological complications. As a group they also experienced cessation of menses prior to age 40 years at a significantly higher rate. The data appear to indicate that the FMR1 gene may play a role in the development and proliferation of oogonia.

X-linked spermine synthase gene (SMS) defect: the first polyamine deficiency syndrome

Polyamines (putrescine, spermidine, spermine) are ubiquitous, simple molecules that interact with a variety of other molecules in the cell, including nucleic acids, phospholipids and proteins. Various studies indicate that polyamines are essential for normal cell growth and differentiation. Furthermore, these molecules, especially spermine, have been shown to modulate ion channel activities of certain cells. Nonetheless, little is known about the specific cellular functions of these compounds, and extensive laboratory investigations have failed to identify a heritable condition in humans in which polyamine synthesis is perturbed. We report the first polyamine deficiency syndrome caused by a defect in spermine synthase (SMS). The defect results from a splice mutation, and is associated with the Snyder-Robinson syndrome (SRS, OMIM_309583), an X-linked mental retardation disorder. The affected males have mild-to-moderate mental retardation (MR), hypotonia, cerebellar circuitry dysfunction, facial asymmetry, thin habitus, osteoporosis, kyphoscoliosis, decreased activity of SMS, correspondingly low levels of intracellular spermine in lymphocytes and fibroblasts, and elevated spermidine/spermine ratios. The clinical features observed in SRS are consistent with cerebellar dysfunction and a defective functioning of red nucleus neurons, which, at least in rats, contain high levels of spermine. Additionally, the presence of MR reflects a role for spermine in cognitive function, possibly by spermine's ability to function as an 'intrinsic gateway' molecule for inward rectifier K(+) channels.

Decline in prevalence of neural tube defects in a high-risk region of the United States

OBJECTIVES

To conduct surveillance for neural tube defects (NTDs) in a high-risk region of the United States and to prevent occurrence and recurrence of NTDs through the periconceptional use of folic acid supplements.

DESIGN

Active and passive methods were used for surveillance of NTD-affected pregnancies and births during a 6-year period (October 1992-September 1998). Individual genetic counseling was used to prevent NTD recurrences and a public awareness campaign was used to reduce NTD occurrences.

SETTING

State of South Carolina.

PATIENTS

All cases of spina bifida, anencephaly, and encephalocele identified among 278 122 live births and fetal deaths to South Carolina residents during 1992-1998 were included.

MAIN OUTCOME MEASURE

Changes in occurrence and recurrence rates during a 6-year period.

RESULTS

Over the 6 years of surveillance, the prevalence rates for NTDs decreased from 1.89 to.95 cases per 1000 live births and fetal deaths. The prevalence decrease is explained primarily by a decrease in cases of spina bifida. Isolated NTDs accounted for 297/360 (82%) NTDs and 63/360 (18%) had at least 1 other structural anomaly. Females predominated among isolated NTDs but the sex distribution was equal among NTD cases with other anomalies. Prevalence rates for whites (1.48 cases per 1000 live births and fetal deaths) were higher than rates for blacks (.87 cases per 1000 live births and fetal deaths). There were no NTD recurrences in 113 subsequent pregnancies to mothers of infants with isolated NTDs who took periconceptional folic acid. The rate of periconceptional folic acid use among women of childbearing years increased from 8% to 35% during the 6-year project period.

CONCLUSION

The prevalence of NTDs in a high-risk region has declined coincident with the increased periconceptional use of folic acid supplements among women of childbearing age.neural tube defects, high-risk region, birth defects, folic acid, spina bifida, anencephaly, encephalocele.

Structural and functional mutations of the perlecan gene cause Schwartz-Jampel syndrome, with myotonic myopathy and chondrodysplasia

Perlecan, a large heparan sulfate proteoglycan, is a component of the basement membrane and other extracellular matrices and has been implicated in multiple biological functions. Mutations in the perlecan gene (HSPG2) cause two classes of skeletal disorders: the relatively mild Schwartz-Jampel syndrome (SJS) and severe neonatal lethal dyssegmental dysplasia, Silverman-Handmaker type (DDSH). SJS is an autosomal recessive skeletal dysplasia characterized by varying degrees of myotonia and chondrodysplasia, and patients with SJS survive. The molecular mechanism underlying the chondrodystrophic myotonia phenotype of SJS is unknown. In the present report, we identify five different mutations that resulted in various forms of perlecan in three unrelated patients with SJS. Heterozygous mutations in two patients with SJS either produced truncated perlecan that lacked domain V or significantly reduced levels of wild-type perlecan. The third patient had a homozygous 7-kb deletion that resulted in reduced amounts of nearly full-length perlecan. Unlike DDSH, the SJS mutations result in different forms of perlecan in reduced levels that are secreted to the extracellular matrix and are likely partially functional. These findings suggest that perlecan has an important role in neuromuscular function and cartilage formation, and they define the molecular basis involved in the difference in the phenotypic severity between DDSH and SJS.