X-linked severe mental retardation and a progressive neurological disorder in a Belgian family: clinical and genetic studies

The combination of X-linked mental retardation (XLMR) and neurological disorders occurs in a number of syndromes. Differential diagnosis mostly depends on clinical data and mapping of responsible genes by linkage analysis. We present a Belgian family with severe XLMR and a progressive neurological disorder with ataxia, spasticity and convulsions. Biochemical investigations, neuroimaging and neuropathology were normal. Linkage analysis pointed to region Xq27-28 as the probable locus for the genetic defect. The sequence of the L1CAM cDNA, a possible candidate gene, proved to be normal in the patients. This suggests the presence of a genetic factor on Xq27-28, different from L1CAM, which can lead to severe XLMR and a progressive neurological disorder.

The X-linked infantile spasms syndrome (MIM 308350) maps to Xp11.4-Xpter in two pedigrees

We report 2 families with X-linked infantile spasms syndrome (X-linked West syndrome). Data from clinical examination, biochemical analysis, neuroimaging, and neuropathology are discussed. In these families, genetic linkage analysis was able to locate the disease gene to the distal part of the short arm of the X chromosome, between Xpter and Xp11.4. This is the first report of linkage with genetic markers in this disorder. Although most cases are sporadic, further unraveling of the genetic background of the familial cases might greatly improve our understanding of infantile spasms.

Intelligence and psychosocial adjustment in velocardiofacial syndrome: a study of 37 children and adolescents with VCFS

We report data on a group of 37 VCFS patients with specific reference to their intelligence, behaviour, and social competence. Fifty five percent of the children had a borderline to normal IQ. Mental retardation (defined as IQ < 70 or > -2 SD below the mean) was found in 45%. In the majority, the mental retardation was mild (38%) and only two patients had moderate mental retardation. Severe mental retardation seems to be rare in VCFS. The present study shows also that the incidence of mental retardation is much higher in the familial than the de novo group. Intelligence is not correlated with the presence or absence of a heart defect. Significantly higher verbal IQs than performance IQs (probably related to deficits in visuospatial-perceptual functioning) were found. Problems in social-emotional functioning and attention were also found. Further longitudinal studies are necessary to provide an accurate prognosis and appropriate intervention for VCFS children.

Interstitial telomeric sequences at the junction site of a jumping translocation

The mechanism(s) for the origin of jumping translocations (JTs) are unknown. To assess the possible involvement of telomeric sequences in the jumping process, metaphases of a patient with hydrops fetalis having a JT were analyzed for the presence of interstitial telomeres. Telomere DNA sequences were detected at the junction sites of the donor and the recipient chromosomes. Interstitial telomeric sequences have so far only been detected in JTs involving chromosome 15q in patients with Prader-Willi syndrome. Our finding of interstitial telomeric sequences in a JT with a chromosome different from chromosome arm 15q in a patient without Prader-Willi syndrome implies that telomere sequences may be common to all telomeric JTs. The possible role of telomeric sequences as a cause of the observed chromosomal mosaicism is discussed.

Trisomy 15 rescue with jumping translocation of distal 15q in Prader-Willi syndrome

We report a patient with Prader-Willi syndrome (PWS) and mosaicism for a de novo jumping translocation of distal chromosome 15q, resulting in partial trisomy for 15q24-qter. A maternal uniparental heterodisomy for chromosome 15 was present in all cells, defining the molecular basis for the PWS in this patient. The translocated distal 15q fragment was of paternal origin and was present as a jumping translocation, involving three different translocation partners, chromosomes 14q, 4q, and 16p. The recipient chromosomes appeared cytogenetically intact and interstitial telomere DNA sequences were present at the breakpoint junctions. This strongly suggests that the initial event leading to the translocation of distal 15q was a non-reciprocal translocation, with fusion between the 15q24 break-point and the telomeres of the recipient chromosomes. These observations are best explained by a partial zygotic trisomy rescue and comprise a previously undescribed mechanism leading to partial trisomy.

Chromosome 22q11 deletion presenting as the Potter sequence

A female fetus with the Potter sequence, caused by unilateral renal agenesis and contralateral multicystic renal dysplasia, was found to have a submicroscopic deletion in chromosome 22q11. The only associated anomaly was agenesis of the uterus and oviducts (Von Mayer-Rokitansky-Küster anomaly). The deletion was inherited from the father, who presented the typical velocardiofacial syndrome phenotype, but no urological anomalies. This observation further extends the clinical spectrum associated with a deletion in 22q11.

Submicroscopic deletion in chromosome 22q11 in trizygous triplet siblings and their father. Clinical variability of 22q11 deletion

A submicroscopic deletion of chromosome 22q11 was demonstrated in three triplets and in their father. Two children had the typical DiGeorge sequence with at least three of the four cardinal features: conotruncal heart disease, hypoplastic thymus and typical facial features. Hypoparathyroidism was present in one of them. The third child had features of both DiGeorge and velo-cardio-facial syndrome (VCFS). The father presented with features compatible with VCFS. This observation further illustrates the wide variability in expression of a submicroscopic deletion of 22q11, even within one family.

Further delineation of renal-coloboma syndrome in patients with extreme variability of phenotype and identical PAX2 mutations

Renal-coloboma syndrome is a recently described autosomal dominant syndrome of abnormal optic nerve and renal development. Two families have been reported with renal-coloboma syndrome and mutations of the PAX2 gene. The PAX2 gene, which encodes a DNA-binding protein, is expressed in the developing ear, CNS, eye, and urogenital tract. Ocular and/or renal abnormalities have been consistently noted in the five reports of patients with renal-coloboma syndrome, to date, but PAX2 expression patterns suggest that auditory and CNS abnormalities may be additional features of renal-coloboma syndrome. To determine whether additional clinical features are associated with PAX2 mutations, we have used PCR-SSCP to identify PAX2 gene mutations in patients. We report here four patients with mutations in exon 2, one of whom has severe ocular and renal disease, microcephaly, and retardation, and another who has ocular and renal disease with high-frequency hearing loss. Unexpectedly, extreme variability in clinical presentation was observed between a mother, her son, and an unrelated patient, all of whom had the same PAX2 mutation as previously described in two siblings with renal-coloboma syndrome. These results suggest that a sequence of seven Gs in PAX2 exon 2 may be particularly prone to mutation.

Prader-Willi syndrome in a child with mosaic trisomy 15 and mosaic triplo-X: a molecular analysis

A 3.3 year old girl with Prader-Willi syndrome (PWS) and mosaicism for two aneuploidies, 47,XXX and 47,XX,+15, is presented. The triplo-X cell line was found in white blood cells and fibroblasts, the trisomy 15 cell line in 50% of the fibroblasts. Using methylation studies of the PWS critical region and by polymorphic microsatellite analysis, the existence of uniparental maternal heterodisomy for chromosome 15 was shown in white blood cells. This provided a molecular explanation for the PWS in this child. In fibrolasts, an additional paternal allele was detected for markers on chromosome 15, which is in agreement with the presence of mosaicism for trisomy 15 in these cells. This example provides direct evidence for trisomic rescue by reduction to disomy as a possible basis for PWS. Whereas the trisomy 15 was caused by a maternal meiosis I error, the triplo-X resulted from a postzygotic gain of a maternal X chromosome, as shown by the finding of two identical maternal X chromosomes in the 47,XXX cell line. Because the triplo-X and the trisomy 15 were present in different cell lines, gain of an X chromosome occurred either in the same cell division as the trisomy 15 rescue or shortly before or after.

Skewed X-chromosome inactivation in female carriers of dyskeratosis congenita

In this study, we report on a family with X-linked dyskeratosis congenita (DC). Linkage analysis with markers in the factor VIII gene at Xq28 yielded a LOD score of 2 at a recombination of 0. Clinical manifestations of DC, such as skin lesions following the Blaschko lines, were present in two obligate carrier females. Highly skewed X inactivation was observed in white blood cells, cultured skin fibroblasts, and buccal mucosa from female carriers of DC in this family. This suggests a critical role for the DC gene in bone marrow-cell and fibroblast-cell proliferation.

Agenesis of corpus callosum and anophthalmia in the asplenia syndrome. A recognisable association?

We present a newborn infant with the asplenia syndrome and unique associated features of corpus callosum agenesis, anophthalmia and coloboma. Previous reports of eye abnormalities or corpus callosum agenesis in patients with asplenia suggest that this may represent a distinct clinically recognisable entity of abnormal lateralisation.

Structure, sequence, and chromosome 19 localization of human USF2 and its rearrangement in a patient with multicystic renal dysplasia

The precise etiology of hydronephrosis caused by pelvi-ureteric junction obstruction is not yet known but there is convincing evidence for a genetic cause, with linkage analysis predicting a hereditary hydronephrosis locus on chromosome 6p. In previous studies, a patient was described with a de novo autosomal t(6;19)(p21;q13.1) translocation and suffering from bilateral multicystic renal dysplasia (MRD) caused by a bilateral complete pelvi-ureteric junction obstruction. In an effort to elucidate a possible correlation between this translocation and hereditary hydronephrosis, we have carried out an extensive molecular characterization of a chromosome 19 cosmid clone previously identified as spanning the translocation in this unique index case. DNA sequencing across a 9.2-kb BamHI fragment that straddles the translocation indicates the presence of DNA sequences with a high degree of similarity to the USF2 gene that encodes the transcription factor USF2 (upstream stimulator factor 2). The genomic structure of USF2 consists of 10 exons distributed over a DNA region of about 11 kb. The putative promoter region is GC-rich and lacks TATA and CCAAT boxes, suggesting that expression of the USF2 gene may be controlled by a typical housekeeping gene promoter. The chromosome 19 breakpoint in the MRD patient appeared to have occurred in intron 7 of the USF2 gene. Northern blot analysis of a variety of human tissues revealed that the USF2 gene is ubiquitously expressed. Furthermore, Northern blot and 3'-RACE analysis of mRNA isolated from lung fibroblasts of the MRD patient failed to detect a fusion transcript involving USF2 sequences, suggesting gene disruption rather than the generation of a fusion gene as a possible underlying mechanism.

Clinical and molecular genetic features of congenital spinal muscular atrophy

A neonate presented with the fetal hypokinesia sequence and signs of spinal muscular atrophy (SMA). Severe pathological changes including ballooned neurons and neuronophagia were found not only in the motor nerve nuclei but also in the thalamic, cerebellar, and brainstem nuclei as well as in the dorsal root ganglia. Direct DNA analysis showed the presence of a chimeric SMN gene, with a rearrangement occurring between exon 7 of the centromeric SMN gene and exon 8 of the telomeric SMN gene. Circumstantial evidence suggests that only a single copy of this gene is present, with transcriptional characteristics of a centromeric SMN gene. In addition, a homozygous deletion in the NAIP genes was demonstrated. This observation demonstrates that at least some cases with fetal hypokinesia and SMA may represent the severe end of a spectrum of disorders caused by deletions in the SMA locus on chromosome 5q13. In addition, these findings are compatible with a modifying role for the centromeric SMN genes and the NAIP genes in the severity of the SMA phenotype.

Cerebellar hypoplasia in a patient with velo-cardio-facial syndrome

Cerebellar malformations feature a large number of syndromes of unknown etiology. A child with hypoplasia of the vermis and left cerebellar hemisphere, severe mental retardation and facial dysmorphism was initially diagnosed as suffering from 3C (Ritscher-Schinzel) syndrome. A deletion in chromosome 22q11 was subsequently demonstrated, establishing the diagnosis of velo-cardio-facial (Shprintzen) syndrome. This observation confirms the previous finding of cerebellar anomalies in Shprintzen syndrome, and suggests an overlap between the VCFS and 3C syndrome. Other signs of VCFS should be looked for in children with cerebellar malformation.

Unusual molecular findings in autosomal recessive spinal muscular atrophy

All three types of autosomal recessive spinal muscular atrophy map to chromosome 5q11.2-q13.3 and are associated with deletions or mutations of the SMN (survival motor neurone) gene. The availability of a test to distinguish between the SMN gene and its nearly identical centromeric copy cBCD541 allows molecular diagnosis. We have analysed patients from 24 Belgian and 34 Turkish families for the presence or absence of a deletion in the SMN gene. A homozygous deletion in the SMN gene was seen in 90% of unrelated SMA patients. A non-radioactive SSCP assay allows for a semiquantitative analysis of the copy number of the centromeric and SMN genes. Hence, direct carrier detection has become feasible under certain conditions. We observed a phenotypically normal male, father of an SMA type I patient, presenting with only a single copy of the SMN gene and lacking both copies of the cBCD541 gene. This illustrates that a reduction of the total number of SMN and cBCD541 genes to a single SMN copy is compatible with normal life. In another SMA type I family, there is evidence for a de novo deletion of the centromeric gene in a normal sib. This observation illustrates the susceptibility of the SMA locus to de novo deletions and rearrangements.

Elevated maternal serum and amniotic fluid alpha-fetoprotein levels in the Denys-Drash syndrome

We report the findings in a child with the Denys-Drash syndrome presenting prenatally with a diaphragmatic hernia, male pseudohermaphroditism, and elevated alpha-fetoprotein levels i amniotic fluid and in maternal serum.

Cohen syndrome: the clinical symptoms and stigmata at a young age

We present the clinical findings and follow-up data of four female children with Cohen syndrome, two sisters and one pair of dizygotic female twins. The most characteristic findings from birth on were as follows: 1. Low-normal growth parameters at birth. 2. Mild hypotonia and evidence of progressive microcephaly with narrow forehead in the first year of life. 3. Neutropenia was present from the beginning, remained unchanged over the years and is not associated with higher susceptibility to infections. 4. Autistic behavior and severe psychomotor retardation up to the age of 2 years. At that age the ocular anomalies with high-grade myopia and chorioretinal dystrophy were diagnosed. Correction of the myopia resulted in a marked catch-up in psychomotor development. 5. After the age of 6 years facial stigmata became more evident with short philtrum of the upper lip and broad and large upper incisors. 6. Tendency to truncular obesity with rest hypotonia and poor muscle development after the ages of 6 to 8 years. The clinical findings and follow-up data in the present four children with Cohen syndrome illustrate that the diagnosis of Cohen syndrome in infancy is very difficult.

Progressive extrapyramidal disorder with primary hypogonadism and alopecia in sibs: a new syndrome?

We report on 2 sibs with consanguineous parents, and an identical progressive extrapyramidal movement disorder with onset in adolescence and associated with progressive alopecia and primary hypogonadism. To our knowledge, this syndrome has not been reported, and probably represents a newly recognized autosomal recessive condition.

Mental retardation, distinct craniofacial dysmorphism, and central nervous system malformation: confirmation of a syndrome

We present a child with severe mental retardation, a central nervous system malformation, signs of ectodermal dysplasia, and a distinct craniofacial dysmorphism. Similar but less pronounced craniofacial features were present in the mildly mentally retarded mother. This observation confirms a previous report of a boy with the same MCA-MR syndrome and suggests X linked or autosomal dominant inheritance.