Molecular and cytogenetic analysis of familial Xp deletions

A Rare Variant of Turner Syndrome in Four Sequential Generations: Effect of the Interplay of Growth Hormone Treatment and Estrogens on Body Proportion

BACKGROUND

Terminal Xp deletion leads to SHOX haploinsufficiency, and when it exceeds Xp22.33 it causes a variant of Turner syndrome (TS) in which gonadal function is preserved and short stature constitutes the major clinical feature.

CASE REPORT

We present a family with vertical transmission of TS that affected six women in four sequential generations. The karyotype was defined as a combination of terminal Xp deletion and terminal Xq duplication: 46,X,rec(X)inv(p21.1q27.3). All affected women had short stature, but had developed spontaneous puberty and normal fertility. Generation IV exclusively received recombinant human growth hormone (rhGH). We investigated the effect of rhGH treatment on skeletal growth and body proportion via the comparison of auxological data from an untreated 39.7-year-old mother to her 14.8-year-old rhGH-treated daughter. The adult height of the daughter was substantially better than that of the mother [160.3 cm (-0.8 SDS) and 150.0 cm (-2.7 SDS), respectively]; however, the disproportion progressed following rhGH treatment and ultimately led to a worse trunk-to-extremities ratio compared with the mother (4.8 and 3.7 SDS, respectively).

CONCLUSION

This rare family confirms the vertical transmission of TS spanning multiple generations. The combination of endogenous estrogen production and exogenous rhGH administration in women with SHOX haploinsufficiency may worsen their body disproportion.

Microscopic chromosome Xp distal deletions--a challenging issue in prenatal genetic counseling

OBJECTIVE

A prenatal diagnosis of chromosome X short arm deletions may present a challenge in prenatal genetic counseling. We present clinical and molecular data of carriers of Xp distal deletions.

METHODS

We assessed prenatal and postnatal phenotypes of individuals from three families with large Xp distal deletions and from a fourth family with a small Xp distal deletion. The work-up included karyotyping, chromosomal microarray analysis, and assessment of the X inactivation pattern.

RESULTS

Five out of eight women with large deletions had a short stature (<3rd percentile). Subjects from one family had developmental and emotional problems. All female carriers with small deletions had markedly short stature, whereas the men had mildly short stature. Chromosomal microarray analysis revealed 11.7-19.3 Mb deletions in three families and a small ~1 Mb deletion in the fourth. The pseudoautosomal region 1 of the X chromosome was deleted in two families with large deletions. X inactivation was skewed in all tested cases with large deletions.

CONCLUSION

Xp distal deletions are mainly associated with short stature. Skewing of the abnormal X chromosome may attenuate the phenotype in cases with large deletions. We suggest that prenatal evaluation in such cases should include sonographic follow-up and assessment of the X inactivation pattern.

The Xp contiguous deletion syndrome and autism

Xp22 nullisomy in males causes a phenotype consistent with the loss of one or more of the genes located in this chromosomal region. Females with similar Xp deletions rarely manifest the same phenotype. Here we describe a 10-year-old girl with a de novo interstitial deletion encompassing Xp22.2p22.32 who presented with autism, moderate mental retardation, and some dysmorphic features. The deletion was delineated by FISH and STR analyses, and the breakpoints were determined using the Agilent 244 K oligonucleotide array. We found that the 5.5 Mb deletion is located on the paternal X chromosome and encompasses 18 genes. Further molecular and cytogenetic analyses showed unfavorable skewing of X-inactivation of the maternal (intact) chromosome. The phenotype of our patient was compared with previously reported female patients with deletions encompassing the same chromosomal region. We discuss the potential role of the genes in the deleted region and X chromosome inactivation in the pathogenesis of the phenotypic abnormalities seen in our patient. Our findings suggest that the severity and the variability of the clinical findings are determined by the size and the parental origin of the deletions as well as the X-inactivation status.

Molecular cytogenetic characterization of two independent karyotypic anomalies in a patient with severe mental retardation and juvenile idiopathic arthritis

We report on a patient with severe mental retardation, dysmorphic features as well as juvenile idiopathic arthritis. G-banding indicated two independent karyotypic anomalies in this patient: an interstitial deletion del(X)(p21p22.3) and a rearrangement involving chromosomes 1 and 7, which represents a direct insertion, ins(7;1)(q36;p13.2p31.2). Non-random inactivation of the paternally derived del(X) chromosome was observed in blood lymphocytes and fibroblasts. High resolution analysis of the rearrangement involving chromosomes 1 and 7 subsequently revealed the additional submicroscopic deletion of at least 5 Mb at the 1p13.2 breakpoint. The deletion occurred on the paternal chromosome and encompasses the PTPN22 gene, already known to be associated with juvenile idiopathic arthritis. Our findings underline the importance of closely investigating the breakpoint regions of apparently balanced rearrangements in patients with abnormal phenotypes since complex chromosomal rearrangements (CCRs) may turn out to be unbalanced.

First reported case of intrachromosomal cryptic inv dup del Xp in a boy with developmental retardation

We report here on a 6-year-old boy referred to the laboratory for karyotyping and SHOX microdeletion testing. The most significant clinical findings in this boy were small stature, Madelung deformity, facial dysmorphism, mild mental retardation and behavioral problems. R-, G- and RTBG-banding chromosome analysis showed a normal male karyotype. Fine molecular characterization, by FISH, of terminal Xp microdeletion revealed an associated partial duplication. Further refinement of the molecular analysis indicated an inverted duplication of the Xp22.31-Xp22.32 (13.7 Mb) region including the STS, VCX-A and KAL1 genes, associated with a terminal Xp deletion Xp22.33-Xpter (3.6 Mb) encompassing the SHOX and ARSE genes. Such rearrangements have been characterized for other chromosomal pairs, but this is the first reported male patient involving the short arm of the X chromosome. Molecular analysis of the maternal and patient's microsatellite markers showed interchromatid mispairing leading to non-allelic homologous recombination to be the most likely mechanism underlying this rearrangement. This case highlights the importance of clinically driven FISH investigations in order to uncover cryptic micro-rearrangements.

Molecular cytogenetic analysis of a familial interstitial deletion Xp22.2-22.3 with a highly variable phenotype in female carriers

We describe a familial interstitial deletion of 7.7-Mb involving Xp22.2-22.3. The deletion was transmitted from an asymptomatic mother to her two children with severe developmental delay, no speech development and autistic behavior. Assessment of the deletion boundaries by FISH and PCR analyses indicated that the deletions encompasses 27 genes. Several of these genes are associated with known disorders, like KAL1 (Kallmann syndrome), steroid sulfatase (STS) (X-linked ichtyosis), and arylsulfatase E (ARSE) (chondrodysplasia punctata). The deletion also includes all four VCX genes (VCX-A, VCX-B1, VCX-B, and VCX-C) and the neuroligin 4 (NLGN4) gene. VCX-A deficiency has been shown previously to be associated with mental retardation and NLGN4 mutations lead to mental retardation in conjunction with autism. Functional deficiency of both MRX genes, VCX-A and NLGN4, are most likely associated with the impaired cognitive development of the patients described here. The phenotype associated with the Xp deletion was highly variable in female carriers and might be attributed to unfavorable X inactivation. However, all the 27 genes included in the deleted interval escape X inactivation and are expressed at variable levels from the normal X chromosome. Thus, the overall X inactivation pattern and inter-individual expression variability of the genes in distal Xp might be determinants of the phenotype associated with the deletion.

A clinical and molecular study of 26 females with Xp deletions with special emphasis on inherited deletions

We have undertaken a clinical study of 26 females with deletions of Xp including five mother-daughter pairs. Cytogenetic and molecular analyses have mapped the breakpoints of the deletions. We determined the parental origin of each abnormality and studied the X-inactivation patterns. We describe the clinical features and compare them with the amount of Xp material lost. We discuss the putative loci for features of Turner syndrome and describe how our series contributes further to their delineation. We conclude that (1) fertility can be retained even with the loss of two-thirds of Xp, thus, if there are genes on Xp for ovarian development, they must be at Xp11-Xp11.2; (2) in our sample of patients there is no evidence to support the existence of a single lymphogenic gene on Xp; (3) there is no evidence for a second stature locus in proximal Xp; (4) there is no evidence to support the existence of a single gene for naevi; (5) we suggest that the interval in Xp21.1-Xp11.4 between DXS997 and DXS1368 may contain a gene conferring a predisposition to hypothyroidism.

A familial contiguous gene deletion syndrome at Xp22.3 characterized by severe learning disabilities and ADHD

We describe a mother and two sons with a 6-Mb terminal deletion of the short arm of the X chromosome. The breakpoint was localized to a region between DXS6837 and sAJ243947 in Xp22.33. The two boys were shown to be deleted for the SHOX and ARSE genes on their X chromosome. Both sons were short in stature and showed mild to moderate skeletal abnormalities. The most significant findings in the younger son were severe learning disabilities and attention deficit hyperactivity disorder (ADHD). The older son tested in the mild mental retardation range and was also affected by ADHD. The VCX-A gene, implicated recently in X-linked nonspecific mental retardation, was found to be present in both boys. The mother's stature was greater than one standard deviation below her target height and she had only subtle radiographic evidence of Madelung deformity. Our findings indicate that loss of the Xp22.3 region is not always associated with the classic presentations of Léri-Weill syndrome, or chondrodysplasia punctata, and that one or more genes involved in learning and attention may reside in Xp22.3.

Successful triplet pregnancy and delivery after oocyte donation in an infertile female with chromosome mosaicism for monosomy X, partial trisomy X, and terminal Xp deletion

OBJECTIVE

To present successful triplet pregnancy and delivery after oocyte donation and IVF in a female with chromosome mosaicism for monosomy X, partial trisomy X, and terminal Xp deletion.

DESIGN

Descriptive case study.

SETTING

Large tertiary care hospital.

PATIENT(S)

A 23-year-old infertile woman with primary amenorrhea, short stature, and a mosaic karyotype of 45,X[10]/46,X,idic(X)(qter-->p22.3::p22.3-->qter)[40]. Fluorescence in situ hybridization investigation of the isodicentric X chromosome revealed terminal Xp deletion.

INTERVENTION(S)

Ultrasound and laparoscopic examinations revealed streak ovaries and a hypoplastic uterus. Oocyte donation and IVF resulted in a triplet pregnancy without major maternal complications.

MAIN OUTCOME MEASURE(S)

Ultrasound and laparoscopy.

RESULT(S)

A cesarean section was performed at 32 weeks gestation because of preterm labor and malpresentation. Three babies were delivered with birth weights of 1,514 g, 1,686 g, and 1,968 g. All infants survived and were healthy at 3 years of age.

CONCLUSION(S)

With careful evaluation and counseling, assisted reproductive technology can be safely used in females with mosaic X chromosome abnormalities and gonadal dysgenesis.

Physical and transcript map of a 2-Mb region in Xp22.1 containing candidate genes for X-linked mental retardation and short stature

Genetic loci for several diseases, including X-linked nonspecific mental retardation and short stature, have been mapped to Xp22.1. In spite of the recent publications of two draft sequences for the human genome, this region seems to be largely unmapped and unsequenced. Here we report an integrated physical and transcript map of approximately 2-Mb from DXS8004 to DXS365. Using sequence tagged site (STS)-content mapping and chromosome walking, we assembled a genomic clone contig of 54 BACs and one cosmid with an estimated 4.5-fold coverage of this region. The minimum tiling path consists of 23 BACs and one cosmid. Onto this contig, we mapped 30 new STSs derived from the unique end-sequences of the BACs, three expressed sequence tags, five genes, and seven CpG islands. This integrated map provides a unique resource for the positional cloning of candidate disease genes mapping to Xp22.1 and is therefore of value for the completion of the genomic sequence of this region.

Short stature in a mother and daughter caused by familial der(X)t(X;X)(p22.1-3;q26)

Deletions of the terminal Xp regions, including the short-stature homeobox (SHOX) gene, were described in families with hereditary Turner syndrome and Léri-Weill syndrome. We report on a 10-2/12-year-old girl and her 37-year-old mother with short stature and no other phenotypic symptoms. In the daugther, additional chromosome material was detected in the pseudoautosomal region of one X chromosome (46,X,add(Xp.22.3)) by chromosome banding analysis. The elongation of the X chromosome consisted of Giemsa dark and bright bands with a length one-fifth of the size of Xp. The karyotype of the mother demonstrated chromosome mosaicism with three cell lines (46,X,add(X)(p22.3) [89]; 45,X [8]; and 47,X,add(X)(p22.3), add(X)(p22.3) [2]). In both daughter and mother, fluorescence in situ hybridization (FISH), together with data from G banding, identified the breakpoints in Xp22.1-3 and Xq26, resulting in a partial trisomy of the terminal region of Xq (Xq26-qter) and a monosomy of the pseudoautosomal region (Xp22.3) with the SHOX gene and the proximal region Xp22.1-3, including the steroidsulfatase gene (STS) and the Kallmann syndrome region. The derivative X chromosome was defined as ish.der(X)t(X;X)(p22.1-3;q26)(yWXD2540-, F20cos-, STS-, 60C10-, 959D10-, 2771+, cos9++). In daughter and mother, the monosomy of region Xp22.1-3 is compatible with fertility and does not cause any other somatic stigmata of the Turner syndrome or Léri-Weill syndrome, except for short stature due to monosomy of the SHOX gene.