Summary of the 1993 ASHG ancillary meeting "recent research on chromosome 4p syndromes and genes"

Impact of chromosome 4p- syndrome on communication and expressive language skills: a preliminary investigation

PURPOSE

The purpose of this investigation was to examine the impact of Chromosome 4p- syndrome on the communication and expressive language phenotype of a large cross-cultural population of children, adolescents, and adults.

METHOD

A large-scale survey study was conducted and a descriptive research design was used to analyze quantitative and qualitative data regarding the communication and expressive language manifestations of 200 children, youth, and adults from 16 countries and Puerto Rico who had been diagnosed with 4p conditions, including Wolf-Hirschhorn syndrome (WHS), Pitt-Rogers-Danks syndrome (PRDS), Proximal 4p Deletion syndrome, and complex chromosomal rearrangements associated with 4p-.

RESULTS

Individuals with Chromosome 4p- syndrome represent a heterogeneous population with complex phenotypic profiles. The majority of the participants exhibited communication and expressive language skills below the 36-month developmental functioning level. A relatively small cohort of the study population exhibited advanced expressive language skills, a finding not reported in the professional literature.

CONCLUSION

Results broaden the spectrum of expressive language skills associated with Chromosome 4p- syndrome and highlight the communication potential of a subset of individuals with 4p abnormalities for development of advanced language structures. It is hypothesized that the largest 4p deletion, which includes the 4p16.3 band and contiguous gene regions, results in the most severely affected expressive language phenotype.

Subtelomeric 6p deletion: clinical, FISH, and array CGH characterization of two cases

Thirty patients have been described with cytogenetically visible deletion of the short arm of chromosome 6. However, subtelomeric 6p deletion detected by subtelomeric specific probes has been reported only twice. We report two new patients with terminal 6p deletion detected by subtelomeric screening using fluorescence in situ hybridization (FISH). The two patients exhibited mental retardation, ocular abnormalities, hearing loss, and a characteristic facial appearance. Detailed FISH analyses with probes covering the distal 6p25 region estimated the size of the terminal deletions to approximately 5.5 Mb and approximately 4.8 Mb. Array-based comparative genomic hybridization (array CGH) was used to confirm the cryptic deletions. Most patients with subtelomeric defects lack a characteristic phenotype. However, some of the subtelomeric deletions result in a specific phenotype, which can direct the clinician towards the diagnosis. Submicroscopic 6p deletion appears to be a recognizable clinical phenotype, and this region should be thoroughly investigated with FISH probes, including at least a subtelomeric 6p probe and a probe covering FOXC1, for patients presenting with a characteristic facial appearance, ocular abnormalities, predominantly anterior-chamber eye defects, hearing loss, and mental retardation.

Mild Wolf-Hirschhorn phenotype and partial GH deficiency in a patient with a 4p terminal deletion

Wolf-Hirschhorn syndrome (WHS) is caused by a variably-sized deletion of chromosome 4 involving band 4p16 whose typical craniofacial features are "Greek warrior helmet appearance" of the nose, microcephaly, and prominent glabella. Almost all patients show mental retardation and pre- and post-natal growth delay. Patient was born at term, after a pregnancy characterized by intra-uterine growth retardation (IUGR). Delivery was uneventful. Developmental delay was evident since the first months of life. At 2 years, he developed generalized tonic-clonic seizures. Because of short stature, low growth velocity and delayed bone age, at 4 years he underwent growth hormone (GH) evaluation. Peak GH after two provocative tests revealed a partial GH deficiency. Clinical observation at 7 years disclosed a distinctive facial appearance, with microcephaly, prominent eyes, and beaked nose. Brain MRI showed left temporal mesial sclerosis. GTG banded karyotype was normal. Because of mental retardation, subtelomeric fluorescence in situ hybridization (FISH) analysis was performed, disclosing a relatively large deletion involving 4p16.2 --> pter (about 4.5 Mb), in the proband, not present in the parents. The smallest deletion detected in a WHS patient thus far includes two candidate genes, WHSC1 and WHSC2. Interestingly, that patient did not show shortness of stature, and that could be due to the haploinsufficiency of other genes localized in the flanking regions. Contribution of GH alterations and possible GH therapy should be further considered in WHS patients.

Telomeres: a diagnosis at the end of the chromosomes

In recent years, subtelomeric rearrangements have been identified as a major cause of mental retardation and/or malformation syndromes. So far, over 2500 subjects with mental retardation have been tested and reported of whom approximately 5% appeared to have a subtelomeric rearrangement. In this review, the clinical aspects of each known (submicroscopic) subtelomeric deletion will be presented and the various methods available for detecting subtelomeric abnormalities will be discussed. Not only will the patients and their families benefit from a good collection and report of the various telomeric abnormalities and their clinical phenotype, but it will also give more insight into the aetiology of mental retardation and malformation syndromes.

An epidemiological study of Wolf-Hirschhorn syndrome: life expectancy and cause of mortality

OBJECTIVE

Early research into Wolf-Hirschhorn syndrome (WHS) described a high mortality and no relationship between deletion size and phenotype. This may need to be revised in the light of improved cytogenetic resolution and medical care. We have collected epidemiological data to allow the calculation of birth incidence and mortality figures. In addition, we have investigated the possibility of a relationship between deletion size and mortality.

METHOD

Information relating to past and present cases diagnosed in the UK was collected by multiple ascertainment.

RESULTS

A total of 159 cases were collected. The status (alive or dead) was determined for 146, of whom 96 are alive, 37 had died, and 13 were detected on prenatal diagnostic tests. A minimum birth incidence of 1 in 95 896 was calculated. The crude infant mortality rate was 17% (23/132) and in the first two years of life the mortality rate was 21% (28/132). Cases with large de novo deletions (proximal to and including p15.2) were more likely to have died than those with smaller deletions (odds ratio=5.7, 95% CI=1.7-19.9) after adjusting for age. A comparison of survival curves for de novo deletions and translocations did not show a statistically significant difference (p=0.11). The median survival time for de novo deletions was 34+ years while for translocation cases it was 18+ years.

CONCLUSIONS

The mortality rate is lower than previously reported. There is a statistically significant relationship between deletion size and overall risk of death in de novo deletion cases. The difference in survival curves between de novo deletions and translocations is not statistically significant.

Trisomy 4 pter-q12 and monosomy of chromosome 13 pter-q12 in a male with deficiency of all blood lymphocyte populations

A six-year-old male presented with multiple congenital anomalies, mental retardation, developmental delay, and an increased frequency of upper and lower respiratory infections and deficiency of all blood lymphocyte populations. Chromosome analysis showed an unbalanced translocation involving chromosomes 4 and 13, leading to partial trisomy for 4pter-q12 and partial monosomy for 13pter-q13 [karyotype, 46,XY,+der(4)t(4;13)(q12;q12),-13)]. The mother is the carrier of a balanced translocation involving chromosomes 4 and 13. The translocation is known to be segregating for three generations in this family. The child was found to have deficiency of all blood lymphocyte populations, but other hemopoietic lineages appeared to be normal. In addition, his fresh T cells were principally CD45RA+, CD62L+, and deficient in the Fas receptor. This deficiency of all blood lymphocyte populations may be due to an overdose of a gene or genes located in the region of chromosome 4 or a partial deficiency of a gene or genes in the region of chromosome 13 that regulate the development of the lymphocyte lineage. Since the mother contributed two copies of chromosomal region 4pter-q12 and no copy of 13pter-q12, the deficiency of all blood lymphocyte populations in our patient may be the result of either uniparental disomy or imprinting. A maternal granduncle with dissimilar dysmorphic features was not lymphopenic but was neutropenic.

4p- syndrome and 9p tetrasomy mosaicism with cleft lip and palate

Chromosome 4p- syndrome is a multiple malformation syndrome associated with partial deletion of the short arm of chromosome 4 (4p-). It is characterized by dysmorphic features and retarded development. Cleft lip and/or palate are the major clinical manifestations. Cases of tetrasomy 9p are extremely rare; the principal clinical manifestations of this condition are characteristic craniofacial abnormalities, generalized hypotonia and severe mental retardation. We present the first case of a female infant with 4p deletion and tetrasomy 9p mosaicism, exhibiting a left-sided cleft lip, alveolus and soft palate. Karyotype analysis of lymphocytes cultured from the patient revealed that she was mosaic: 86% of the cells were 46, XX, add (4) (p15.32) and 14% were 47, XX, add (4) (p15.32), +idic (9)(q12). The G-banding pattern appeared consistent with either translocation or partial proximal deletion of 4p. In order to make a definitive cytogenetic diagnosis of isodicentric chromosome 9, fluorescence in situ hybridization (FISH) was applied. At 8 months, when the patient weighed 4.3 kg, her cleft lip was repaired. Before and after surgery there were no seizures, and the postoperative course was uneventful.

Three-year-old girl with partial trisomy 4p and partial monosomy 8p with resemblance to Brachmann-de Lange syndrome--another locus for Brachmann-de Lange syndrome on 4p?

We describe a 3-year-old girl with partial trisomy 4p and partial monosomy 8p who had prenatal and postnatal growth retardation, mental retardation, no speech development, mild synophrys, hirsutism, apparently low-set ears, dysphonic hoarse voice, hyperactivity, and small hands with proximal placement of the thumbs. She had recurrent lung infections, due to earlier aspiration and immune deficiency (chronic granulomatous disease). Cytogenetic findings in this and other cases with suggestive phenotype may point to an additional locus for Brachmann-de Lange phenotype.

Chromosome breakage hotspots and delineation of the critical region for the 9p-deletion syndrome

The clinical features of the 9p-deletion syndrome include dysmorphic facial features (trigonocephaly, midface hypoplasia, upward-slanting palpebral fissures, and a long philtrum) and mental retardation. The majority of these patients appear to have similar cytogenetic breakpoints in 9p22, but some cases show phenotypic heterogeneity. To define the breakpoints of the deleted chromosomes, we studied 24 patients with a deletion of 9p, by high-resolution cytogenetics, FISH with 19 YACs, and PCR using 25 different sequence-tagged sites. Of 10 different breakpoints identified, 9 were localized within an approximately 5-Mb region, in 9p22-p23, that encompasses the interval between D9S1869 (telomeric) and D9S162 (centromeric). Eight unrelated patients had a breakpoint (group 1) in the same interval, between D9S274 (948h1) and D9S285 (767f2), suggesting a chromosome-breakage hotspot. Among 12 patients, seven different breakpoints (groups 3-9) were localized to a 2-Mb genomic region between D9S1709 and D9S162, which identified a breakpoint-cluster region. The critical region for the 9p-deletion syndrome maps to a 4-6-Mb region in 9p22-p23. The results from this study have provided insight into both the heterogeneous nature of the breakage in this deletion syndrome and the resultant phenotype-karyotype correlations.

Antibody deficiency in Wolf-Hirschhorn syndrome

We identified antibody deficiencies in 9 of 13 infection-prone children with Wolf-Hirschhorn syndrome (4p-monosomy). Eight of the immunodeficient children were identified by a questionnaire sent to 190 families with an affected child. Two of the children had common variable immunodeficiency, one had IgA and IgG2 subclass deficiency, three had IgA deficiency, and three had impaired polysaccharide responsiveness. T-cell immunity was normal. The association of antibody defects with Wolf-Hirschhorn syndrome suggests a regulatory gene within the deleted chromosome region that affects the B cell system.

New overgrowth syndrome and FGFR3 dosage effect

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Molecular cloning, chromosomal mapping and developmental expression of BAPX1, a novel human homeobox-containing gene homologous to Drosophila bagpipe

We describe here the cloning of the human BAPX1 gene, a homologue of the Drosophila bagpipe gene which has 87% aa identity within the homeodomain relative to the fly gene. We recently have identified the murine bagpipe homolog. The predicted aa sequence of the human gene has 85% overall identity to the murine gene, with 100% identity in the homeodomain. In mouse, this gene maps to the proximal portion of chromosome 5. We show that the human gene maps to 4p16.1, the human region syntenic with mouse chromosome 5. Expression of BAPX1 was evaluated during human embryonic development by RT-PCR analysis and by RNA in situ hybridization. RT-PCR analysis showed that BAPX1 is expressed in embryo tissues, particularly the limb, and at a lower level in an embryonic lung cell line. RNA in situ hybridization revealed that BAPX1 is predominantly expressed in mesenchymal condensations of the fetal limb and axial skeleton, and in lateral plate mesoderm giving rise to visceral muscle. The expression pattern of BAPX1 combined with the chromosomal localization to 4p16.1, where several human genetic diseases involving dysmorphology of the skeleton have been assigned, raises the potential of it being a candidate gene for one of these disorders. O

On two patients with and without the classical Wolf-Hirschhorn syndrome (WHS) sharing the same chromosome 4p16.3 specific probe deletion: evidence of a contiguous gene deletion syndrome

We report here on phenotype-karyotype correlations in two patients with and without complete features of the WHS but sharing the lack of a specific cosmic probe (D4S96/D4Z1) from 4p16.3. These findings indicate that WHS is true a contiguous gene deletion syndrome in nature and expression.