Non-syndromic X-linked mental retardation associated with a missense mutation (P312L) in the FGD1 gene

Three brothers with non-syndromal X-linked mental retardation were found to have a novel missense mutation in FGD1, the gene associated with the Aarskog syndrome. Although the brothers have short stature and small feet, they lack distinct craniofacial, skeletal or genital findings suggestive of Aarskog syndrome. Their mother, the only obligate carrier available for testing, has the FGD1 mutation. The mutation, a C934T base change in exon 4, results in the proline at position 312 to be substituted with a leucine. This missense mutation is predicted to eliminate a beta-turn, creating an extra-long stretch of coiled sequence which may affect the orientations of an SH3 (Src homology 3) binding domain and the first structural conserved region. A new molecular defect associated with non-syndromal X-linked mental retardation affords an opportunity to seek specific diagnosis in males with previously unexplained developmental delays and this opens further predictive tests in families at risk.

Splitting and lumping in the nosology of XLMR

Although it is assumed that genes that influence cognitive function are ubiquitous in the human genome, to date, more such genes have been found on the X chromosome than on any other comparable segment of the autosomes. This is in large measure because of the power of hemizygosity in exposing mutations of X-linked genes in males. Clinical manifestations, mapping of gene loci by linkage analysis or chromosome rearrangements, and gene identification by positional cloning or mutational analysis of candidate genes have permitted extensive lumping and splitting within the large and heterogeneous category of X-linked mental retardation (XLMR). Approximately 130 XLMR syndromes have been identified, 25 gene loci have been mapped and cloned, and 55 other loci have been mapped but not cloned. Well-recognized syndromes (e.g., Fragile X and Coffin-Lowry syndromes) and syndromes represented by only a single family (e.g., Arena and monoamine oxidase-A syndromes) are among these more or less well-defined entities. In addition, more than 75 families with nonsyndromal XLMR have been regionally mapped and 7 causative genes have been identified.

Split hand/split foot malformation with hearing loss: first report of families linked to the SHFM1 locus in 7q21

Developmental anomalies of the appendicular skeleton are among the most common and easily ascertained birth defects. Split hand/split foot malformations, distinctive in having deficiency of the central rays, occur as isolated anomalies and as one component of multisystem syndromes. The clinical and molecular characterization of a new syndrome, found in two unrelated families, consisting of split foot with hearing loss, is presented here. As in other split hand/split foot conditions, variable expression and reduced penetrance is notable. In the larger family, variably expressed split foot malformations were found in 6 of 11 gene carriers. and mild-to-moderate sensorineural hearing loss in 4. Split hand and cleft lip/palate in one individual and tibial deficiency in another suggest that these malformations are uncommon components of the syndrome. Ectodermal abnormalities did not occur. In the second family, variable split foot was observed in 3 of 4 gene carriers, and sensorineural deafness was present in 3. Split hand was only seen in a gene carrier who also had split foot and deafness. One gene carrier only had deafness. The gene for split hand split foot with sensorineural hearing loss was linked to markers in 7q21 in both families, with a combined (maximum LOD score of 4.37 at theta = 0.0 for locus D7S527) at 80% penetrance. Efforts to identify the responsible gene have not yet been successful.

Spectrum of Schwartz-Jampel syndrome includes micromelic chondrodysplasia, kyphomelic dysplasia, and Burton disease

Follow-up and re-evaluation of four patients originally described as examples of severe infantile "micromelic chondrodysplasia" resembling Kniest disease, "kyphomelic dysplasia," and "Burton skeletal dysplasia" revealed the diagnosis of Schwartz-Jampel syndrome (SJS, myotonic chondrodysplasia) in all of them. SJS may be suspected in neonates with Kniest-like chondrodysplasia, congenital bowing of shortened femora and tibiae, and facial manifestations consisting of a small mouth, micrognathia, and possibly pursed lips. The disorder must be differentiated from the Stüve-Wiedemann syndrome, a genetically distinct myotonic chondrodysplasia with similar clinical but different skeletal changes and an unfavorable early prognosis. The demise of "kyphomelic dysplasia" as a nosological entity reemphasizes the symptomatic nature of congenital bowing of the long bones.

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.

A new X linked mental retardation (XLMR) syndrome with short stature, small testes, muscle wasting, and tremor localises to Xq24-q25

METHODS

A large family is described in which mental retardation segregates as an X linked trait. Six affected males in three generations were studied by linkage and clinical examination.

RESULTS

Characteristic clinical features include short stature, prominent lower lip, small testes, muscle wasting of the lower legs, kyphosis, joint hyperextensibility, abnormal gait, tremor, and decreased fine motor coordination. Affected subjects also had impaired speech and decreased attention span. A carrier female was mildly affected. A similar disorder was not found on review of our XLMR Database of 124 syndromes. Linkage analysis of 37 markers resulted in a lod score of 2.80 at DXS1212 and 2.76 at DXS425. The limiting markers were DXS424 and DXS1047. Ten of 124 XLMR syndromes and eight of 58 MRX families overlap this region.

CONCLUSIONS

In summary, this family appears to have a new XLMR syndrome localising to Xq24-q25.

The HOPA gene dodecamer duplication is not a significant etiological factor in autism

A recent study has suggested that a dodecamer duplication in the HOPA gene in Xq13 may occur in a significant portion of male patients with autism. We have determined the incidence of this duplication in 202 patients from the South Carolina Autism Study. The incidence of the duplication was not significantly different between patients and controls. Three of the female patients inherited the duplication from nonautistic fathers. In addition, there was no systematic skewing of X inactivation in the female patients with the duplication, or in nonautistic mothers and sisters with the duplication. These findings suggest that the dodecamer duplication in the HOPA gene does not play a significant role in the etiology of autism.

Evidence that a dodecamer duplication in the gene HOPA in Xq13 is not associated with mental retardation

A recent study suggested that a dodecamer duplication in exon 42 of the HOPA gene in Xq13 may be a significant factor in the etiology of X-linked mental retardation. In an effort to investigate this possibility, we determined the incidence of the dodecamer duplication in cohorts of non-fragile X males with mental retardation from three countries, cohorts of fragile X males from two countries, 43 probands from families with X-linked mental retardation and control cohorts from three countries. The duplication was found in 3.6-4.0% of male patients from two non-fragile X groups (Italy and South Carolina), in 1.2% from another non-fragile X group (South Africa), but in no male patients from families with X-linked mental retardation (South Carolina). The dodecamer duplication was also found in several white males with fragile X syndrome from France (5%) and South Africa (22.2%). Additionally, the duplication was found in 1.5% of South Carolinian newborn males, 2.5% South Carolinian male college students, 5% Italian male controls and 4.5% of the white South African controls. None of the black South African non-fragile X individuals with mental retardation, the fragile X or the control samples tested carried the duplication, suggesting that the duplication is rare in the black South African population. The incidence of the duplication was not significantly different between any of the groups in the study. Therefore, results of our studies in four different populations do not corroborate the findings of the previous study, and indicate that the HOPA dodecamer duplication does not convey an increased susceptibility to mental retardation.

X linked severe mental retardation, craniofacial dysmorphology, epilepsy, ophthalmoplegia, and cerebellar atrophy in a large South African kindred is localised to Xq24-q27

To date over 150 X linked mental retardation (XLMR) conditions have been documented. We describe a five generation South African family with XLMR, comprising 16 affected males and 10 carrier females. The clinical features common to the 16 males included profound mental retardation (100%), mutism despite apparently normal hearing (100%), grand mal epilepsy (87.5%), and limited life expectancy (68.8%). Of the four affected males examined, all had mild craniofacial dysmorphology and three were noted to have bilateral ophthalmoplegia and truncal ataxia. Three of 10 obligate female carriers had mild mental retardation. Cerebellar and brain stem atrophy was shown by cranial imaging and postmortem examination. Linkage analysis shows the gene to be located between markers DXS424 (Xq24) and DXS548 (Xq27.3), with a maximum two point lod score of 3.10.

Molecular cloning and characterization of TRPC5 (HTRP5), the human homologue of a mouse brain receptor-activated capacitative Ca2+ entry channel

A novel human gene, TRPC5, was cloned from the region of Xq23 that contains loci for nonsyndromic mental retardation (MRX47 and MRX35) and two genes, DCX and HPAK3, implicated in two X-linked disorders (LISX and MRX30). Within a single YAC, we have determined the order cen-HPAK3(5'-3')-DCX(3'-5')-DXS7012E-TRPC5(3'-5' )-ter. TRPC5 encodes a 974-residue novel human protein (111.5 kDa predicted mass) and displays 99% homology with mouse TRP5, (MGD-approved symbol Trrp5) a novel member of a family of receptor-activated Ca2+ channels. It contains eight transmembrane domains, including a putative pore region. A transcript larger than 9.5 kb is observed only in fetal and adult human brain, with a relatively higher level in the adult human cerebellum. We devised an efficient method, Incorporation PCR SSCP (IPS), for detection of gene alterations. Five single-nucleotide variations in the TRPC5 gene were identified in males with mental retardation. However, these were found to be polymorphic variants. Exclusive expression of the TRPC5 gene in developing and adult brain suggests a possible role during development and provides a candidate gene for instances of mental retardation and other developmental defects.

X-linked mental retardation syndrome with short stature, small hands and feet, seizures, cleft palate, and glaucoma is linked to Xq28

Of the gene-rich regions of the human genome, Xq28 is the most densely mapped. Mutations of genes in this band are responsible for 10 syndromal forms of mental retardation and 5 nonsyndromal forms. Clinical and molecular studies reported here add an additional syndromic form of X-linked mental retardation (XLMR) to this region. The condition comprises short stature, small hands and feet, seizures, cleft palate, and glaucoma. One affected male died at age 19 years in status epilepticus, but others have survived to old age. Carrier females do not have somatic anomalies or mental impairment. The gene is localized to the terminal 8 Mb of Xq28 with markers distal to DXS8011 showing linkage to the disorder with a lod score of 2.11 at zero recombination.

Gene for apparently nonsyndromic X-linked mental retardation (MRX32) maps to an 18-Mb region of Xp21.2-p22

We studied a family with 11 males having X-linked mental retardation (XLMR) using microsatellite markers. Aside from the mental retardation, the affected males do not appear to differ from their unaffected brothers or uncles. The gene for this XLMR condition has been linked to DXS451 in Xp22.13 with a lod score of 5.18 at straight theta = 0. Recombination was detected at DXS992 (Xp21.3) and DXS1053 (Xp22.2), thereby defining the limits of the localization. This family is considered to have nonsyndromic XLMR and has been assigned the designation MRX32.

XLMR syndrome characterized by multiple respiratory infections, hypertelorism, severe CNS deterioration and early death localizes to distal Xq28

We report on a family with severe X-linked mental retardation (XLMR) and progressive, severe central nervous system deterioration. Three of the five affected males died of secondary complications before the age of 10 years and none have survived past the age of 10. These complications included swallowing dysfunction and gastroesophageal reflux with secondary recurrent respiratory infections. In addition, hypotonia and a mild myopathy were also present. All had a characteristic facies, including downslanting palpebral fissures, hypertelorism, and a short nose with a low nasal bridge. The two older boys showed cerebral atrophy by CT. No metabolic abnormalities were identified. Three obligate carriers had an IQ less than 80. The causal gene has been localized distal to DXS8103 in Xq28, a region spanning 5cM. No other XLMR disorder with these manifestations have been localized to this region and this appears to be a new disorder.

X-linked mental retardation syndrome with seizures, hypogammaglobulinemia, and progressive gait disturbance is regionally mapped between xq21.33 and Xq23

We identified a family with three males in two generations with moderate mental retardation. The two oldest were first cousins whose mothers were sisters. The third affected was a grandson through a daughter of one of the sisters, strongly suggesting X- linked inheritance. The affected males had prominent glabella, synophrys, prognathism, generalized hirsutism, and bilateral single palmar creases. All developed seizures in childhood. The two oldest have had a slow deterioration in neurological status with poor gait and balance and progressive weakness. No deterioration in their mental status has been observed. The oldest had cerebellar atrophy confirmed on computed tomography and magnetic resonance imaging scans of the brain and prolonged nerve conduction velocity. Two of the males had hypogammaglobulinemia (IgA deficient). Two-point linkage analysis using 27 microsatellite markers on the X chromosome resulted in a maximum LOD score of 2.23 at straight theta = 0 for locus DSX101. Recombination was observed at locus DSX1170 in Xq21.33 and locus DXS8067 in Xq23. We conclude that this family represents an X-linked disorder associated with a recognizable phenotype, progressive neurological deterioration, and variable hypogammaglobulinemia. The gene appears to lie between Xq21.33 and Xq23.

XLMR database

The computer database on X-linked mental retardation (XLMR) disorders developed by Arena and Lubs in 1991 has now been updated to include all currently known XLMR disorders and nonspecific (MRX) families. Currently, it includes 123 syndromes, 59 nonspecific XLMR families, and 60 families from the Miami/Greenwood study. The older clinical reports have been reviewed and revised. The search mechanism has also been revised and now includes 740 individual "keywords." Each of these keywords recognizes several of clinical descriptive terms, as used in published literature reports. Searches can be made according to any clinical finding or combination of findings. For each disorder, the database presents a graphic display that contains a revised and more complete set of clinical findings, references, keywords, map localization, molecular information, access to pictures, and OMIM number.

X-linked mental retardation with variable stature, head circumference, and testicular volume linked to Xq12-q21

Clinical and molecular studies are reported on a family with X-linked mental retardation (XLMR) in which there are eight affected males in three generations. Although the males have somatic manifestations, these are variable and in most cases do not allow clear distinction of affected and unaffected males. Affected males are shorter and have a smaller head circumference. Several also have a sloping forehead (5/8), hearing loss (3/8), cupped ears (2/8), and small testes (4/6). An LOD score of 4.41 with zero recombination was obtained at locus DXS1166 in Xq13.2. This family highlights the difficulty in classifying XLMR conditions as either nonsyndromic or syndromic because of the variable somatic manifestations observed in the affected males.

Renpenning syndrome maps to Xp11

Mutations in genes on the X chromosome are believed to be responsible for the excess of males among individuals with mental retardation. Such genes are numerous, certainly >100, and cause both syndromal and nonsyndromal types of mental retardation. Clinical and molecular studies have been conducted on the Mennonite family with X-linked mental retardation (XLMR) reported, in 1962, by Renpenning et al. The clinical phenotype includes severe mental retardation, microcephaly, up-slanting palpebral fissures, small testes, and stature shorter than that of nonaffected males. Major malformations, neuromuscular abnormalities, and behavioral disturbances were not seen. Longevity is not impaired. Carrier females do not show heterozygote manifestations. The syndrome maps to Xp11.2-p11.4, with a maximum LOD score of 3.21 (recombination fraction 0) for markers between DXS1039 and DXS1068. Renpenning syndrome (also known as "MRXS8"; gene RENS1, MIM 309500) shares phenotypic manifestations with several other XLMR syndromes, notably the Sutherland-Haan syndrome. In none of these entities has the responsible gene been isolated; hence, the possibility that two or more of them may be allelic cannot be excluded at present.

Analysis of the human Sonic Hedgehog coding and promoter regions in sacral agenesis, triphalangeal thumb, and mirror polydactyly

The human Sonic Hedgehog gene (SHH) is one of the vertebrate homologs related to the Drosophila segment polarity gene hedgehog. The entire coding and promoter region of the SHH gene, including 2 kb 5' of the transcriptional start site has been screened for mutations in families with autosomal dominant sacral agenesis and autosomal dominant triphalangeal thumb, two conditions previously known to be linked to 7q36. We have also studied the SHH gene in five families with mirror polydactyly associated with tibial hemimelia and in 51 unrelated patients with neural tube defects. Except for two sequence variants in exon 3, no mutations were found in these disease categories. OFF

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.

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.

A new X linked recessive syndrome of mental retardation and mild dysmorphism maps to Xq28

Efforts to understand the genetic basis of mental retardation are greatly assisted by the identification of families with multiple relatives with mental retardation that clinical geneticists encounter in the routine practice of their profession. Here we describe a linkage study of a four generation family in which X linked recessive mental retardation (XLMR) is associated with minor dysmorphism and premature death of the affected males. Microsatellite based polymorphic loci evenly spaced over the entire X chromosome were used initially to detect linkage to Xq28. Further analysis identified a haplotype of Xq28 markers bounded proximally by locus DXS1113 and distally by DXS1108 that cosegregated with XLMR in this family. Two point lod scores > 3.0 provided strong evidence that the gene locus responsible for XLMR in this family is within this 7 Mb region of Xq28. The minor anomalies noted in some affected males were not distinctive enough to suggest a unique syndrome. None of our patients had features of the Waisman-Laxova syndrome or the PPM-X syndrome. The possibility of allelism with any of the five other non-specific XLMR syndromes (MRX3, MRX16, MRX25, MRX28, and MRX41) mapped to Xq28 could not be excluded. While the recognition of a gene responsible for this disorder needs much additional work, multiple female relatives at risk in this family benefit immediately from knowing their genotype and heterozygotes will have the opportunity to undergo prenatal diagnosis.

Weather Variables Associated with Infection of Tomato Fruit by Colletotrichum coccodes

Field experiments were conducted to determine the relationship of tomato anthracnose to weather variables. Sixteen potted tomato plants were exposed to field conditions within rows of tomato plants for 4 consecutive days at various time periods during the 1993 and 1994 summer growing seasons. Incidence of fruit infection by Colletotrichum coccodes was correlated with rain variables (amount and duration of rain) alone and in combination with other meteorological factors. The best fitting regression equation, accounting for 72% of the variation in anthracnose incidence (arcsine-square root transformed), was Y = 111.77 - 1.16 HNRo, in which HNRo is the numbers of hours during which no rainfall occurs within 4-day intervals that tomato fruit were exposed to field conditions in central Pennsylvania.

Arch fingerprints, hypotonia, and areflexia associated with X linked mental retardation

A syndrome with distinctive facies, poor muscle tone, absent deep tendon reflexes, tapered fingers, excessive fingerprint arches, genu valgum and mild-moderate mental retardation has occurred in four males in two generations of a white family of European ancestry. The facies are characterised by square configuration, tented upper lip, and thickening of the helices, upper eyelids, and alae nasi. At birth and at maturity, growth (head circumference, height, weight) of affected males is comparable to or greater than unaffected male sibs. Moderate impairment of cognitive function was documented (IQ scores between 40-51). Carriers show no heterozygote manifestations. This X linked condition appears to be different from other syndromes with mental retardation, although there are certain similarities with the alpha thalassaemia-mental retardation syndrome (ATR-X). Linkage analysis found tight linkage to DXS1166 and DXS995 in Xq13 and Xq21 respectively.