Two patients with ring chromosome 15 syndrome

Evidence for NR2F2/COUP-TFII involvement in human testis development

NR2F2 encodes COUP-TFII, an orphan nuclear receptor required for the development of the steroidogenic lineages of the murine fetal testes and ovaries. Pathogenic variants in human NR2F2 are associated with testis formation in 46,XX individuals, however, the function of COUP-TFII in the human testis is unknown. We report a de novo heterozygous variant in NR2F2 (c.737G > A, p.Arg246His) in a 46,XY under-masculinized boy with primary hypogonadism. The variant, located within the ligand-binding domain, is predicted to be highly damaging. In vitro studies indicated that the mutation does not impact the stability or subcellular localization of the protein. NR5A1, a related nuclear receptor that is a key factor in gonad formation and function, is known to physically interact with COUP-TFII to regulate gene expression. The mutant protein did not affect the physical interaction with NR5A1. However, in-vitro assays demonstrated that the mutant protein significantly loses the inhibitory effect on NR5A1-mediated activation of both the LHB and INSL3 promoters. The data support a role for COUP-TFII in human testis formation. Although mutually antagonistic sets of genes are known to regulate testis and ovarian pathways, we extend the list of genes, that together with NR5A1 and WT1, are associated with both 46,XX and 46,XY DSD.

Response to growth hormone therapy in ring chromosome 15: Review and evidence from a new case on possible beneficial effect in neurodevelopment

Type 1 Insulin-like Growth Factor Receptor(IGF1R) plays a fundamental role in normal growth and development. Its disruption is usually characterized by severe intrauterine and postnatal growth retardation, microcephaly and neurodevelopmental delay.The efficacy of recombinant human growth hormone treatment remains a challenge for children with IGF1 resistance and pathogenic mutations of IGF1R, with limited data in patients carrying the most severe form of IGF1R defect, the ring chromosome 15.

SUBJECT AND METHOD

We tested a high dose of rhGH in a new patient with ring chromosome 15, as confirmed by karyotype and CGH array. We performed a systematic review, and all published r(15) syndrome cases treated by growth hormone(GH) up to April 2023 were searched, and their response to GH therapy was recorded and summarized.

RESULTS

Twelve patients with ring chromosome 15 received GH therapy according to a literature review. We expand the spectrum by the 13th case treated by GH, and we report an impressive improvement in intellectual performance and progressive catch-up growth after 5 and 20 months of follow-up. By introducing our new case in the analysis, the sex ratio was 3:10, and GH therapy was started at the age of 5.5 (3/9.4) (years) for an age of diagnosis of 4.75 (1.3/9.5) (years). The height before GH therapy was -5.1(-5.9/-4.1) SDS. The median duration of treatment was 1.7(0.9/2) (years), with a median height gain of 1(0.3/1.8) SDS and an improvement in growth velocity of 4.1(2.8/5.3) (cm/year).

CONCLUSION

GH seems to be effective for r(15) syndrome patients with short stature.

Rare pathology derived from a ring chromosome 15. Clinical, genomic and protein interactome of genes associated with the phenotype

The case of a 4-year-two-month-old female patient is presented, who consulted for a special phenotype: psychomotor retardation, short stature, microcephaly, large and low-set ears, small forehead, prominent brow ridges, labial commissure open, ocular hypertelorism, short neck, mammary hypertelorism and pectus excavatum. The objective of this study is to analyze a patient with unusual phenotypic traits, through physical examination, comparative analysis with other cases, and genetic studies. The cytogenetic study revealed a mosaic karyotype, mos 46,XX,r(15)(q26.3)/46,XX with the presence of the ring in 83%. The genetic mapping array study identified the loss of 3.5 Mb in 15q26.3. Among the genes lost in the terminal region of 15q, an interaction between their protein products was evidenced according to the STRING analysis. This is the second case of a ring chromosome 15 reported in Ecuador. And it would be the 101st in the world since 1966. The special phenotype of these individuals is related to the amount of genetic material lost. The genes involved in the formation of the ring, as well as the proteins that determine these genes and the relationships in different cellular pathways, are analyzed in silico in order to understand the pathophysiology of this disorder. Its diagnosis is mostly postnatal, so the clinical approach differs individually according to the symptoms and signs that appear.

The phenotype and rhGH treatment response of ring Chromosome 15 Syndrome: Case report and literature review

Background

Ring chromosome 15 [r (15)] is an uncommon finding with various clinical manifestations. A common phenotype for these patients has not been established and data on the efficacy of recombinant human growth hormone (rhGH) treatment in patients with r (15) syndrome are limited.

Methods

One short stature patient in our hospital with r (15) syndrome by whole exome sequencing (WES) and karyotype examination was included. All published r (15) syndrome cases as of March 15, 2021, were searched, and their clinical information was recorded and summarized.

Results

One 11.5‐year‐old female with prenatal and postnatal growth retardation, ventricular septal defect, intellectual disability, downward corners, short fifth metacarpal bone, scattered milk coffee spots, and a right ovarian cyst was included. Her height was 126.9 cm (−3.45 SDS). Karyotype analysis showed 46, XX, r (15). WES revealed a 4.5 Mb heterozygous deletion in the chromosome 15q26.2‐q26.3 region, encompassing genes from ARRDC4 to OR4F15. Gonadotrophin‐releasing hormone analogue (triptorelin) and rhGH were administered for 6 months. The height has increased 3.8 cm (+0.2SDS) and the calculated growth rate has improved from 4.7 to 7.6 cm/y. The literature review indicated the main clinical manifestations of r (15) syndrome with prenatal and postnatal growth retardation, characteristic craniofacial features, and multisystem abnormalities, and rhGH treatment is beneficial for r (15) syndrome patients with short stature.

Conclusion

We delineate the clinical spectrum of r (15) syndrome with the identification of an additional individual and rhGH treatment is beneficial for r (15) syndrome patients with short stature.

Disorders of IGFs and IGF-1R signaling pathways

The insulin-like growth factor (IGF) system comprises two ligands, IGF-I and IGF-II, that regulate multiple physiological processes, including mammalian development, metabolism and growth, through the type 1 IGF receptor (IGF-1R). The growth hormone (GH)-IGF-I axis is the major regulator of longitudinal growth. IGF-II is expressed in many tissues, notably the placenta, to regulate human pre- and post-natal growth and development. This review provides a brief introduction to the IGF system and summarizes findings from reports arising from recent larger genomic sequencing studies of human genetic mutations in IGF1 and IGF2 and genes of proteins regulating IGF action, namely the IGF-1R, IGF-1R signaling pathway components and the IGF binding proteins (IGFBPs). A perspective on the effect of homozygous mutations on structure and function of the IGFs and IGF-1R is also given and this is related to the effects on growth.

Increasing knowledge in IGF1R defects: lessons from 35 new patients

BACKGROUND

The type 1 insulin-like growth factor receptor (IGF1R) is a keystone of fetal growth regulation by mediating the effects of IGF-I and IGF-II. Recently, a cohort of patients carrying an IGF1R defect was described, from which a clinical score was established for diagnosis. We assessed this score in a large cohort of patients with identified IGF1R defects, as no external validation was available. Furthermore, we aimed to develop a functional test to allow the classification of variants of unknown significance (VUS) in vitro.

METHODS

DNA was tested for either deletions or single nucleotide variant (SNV) and the phosphorylation of downstream pathways studied after stimulation with IGF-I by western blot analysis of fibroblast of nine patients.

RESULTS

We detected 21 IGF1R defects in 35 patients, including 8 deletions and 10 heterozygous, 1 homozygous and 1 compound-heterozygous SNVs. The main clinical characteristics of these patients were being born small for gestational age (90.9%), short stature (88.2%) and microcephaly (74.1%). Feeding difficulties and varying degrees of developmental delay were highly prevalent (54.5%). There were no differences in phenotypes between patients with deletions and SNVs of IGF1R. Functional studies showed that the SNVs tested were associated with decreased AKT phosphorylation.

CONCLUSION

We report eight new pathogenic variants of IGF1R and an original case with a homozygous SNV. We found the recently proposed clinical score to be accurate for the diagnosis of IGF1R defects with a sensitivity of 95.2%. We developed an efficient functional test to assess the pathogenicity of SNVs, which is useful, especially for VUS.

Ring chromosome 15 - cytogenetics and mapping arrays: a case report and review of the literature

BACKGROUND

Ring chromosome 15 has been associated in previous studies with different clinical characteristic such as cardiac problems, digit and musculoskeletal abnormalities, and mental and motor problems among others. Only 97 clinical cases of ring chromosome 15 syndrome have been reported since 1966 and a common phenotype for these patients has not been established.

CASE PRESENTATION

The present case report describes a 15-month-old girl from the Amazon region of Ecuador, of Mestizo ancestry, who after cytogenetic tests showed a 46,XX,r(15) karyotype in more than 70% of metaphases observed. Her parents were healthy and non-related. The pregnancy was complicated and was positive for intrauterine growth retardation. Her birth weight was 1950 g, her length was 43.5 cm, and she had a head circumference of 29.3. In addition to postnatal growth delay, she had scant frontal hair, small eyes, hypertelorism, low-set of ears, flattened nasal bridge, anteverted nostrils, down-turned mouth, three café au lait spots, and delayed dentition.

CONCLUSIONS

Despite the frequency of some phenotypes expressed in the different clinical cases reviewed and the present case, a common phenotype for patients with ring 15 could not be determined and it is restricted to the region of the chromosome lost during the ring formation.

The normality of sperm in an infertile man with ring chromosome 15: a case report

PURPOSE

The purpose of this report is to analyze the chromosome status and fertilization capability of sperm obtained from an infertile male patient with ring chromosome 15.

METHODS

This was a case report at a private in vitro fertilization clinic. A man diagnosed with severe oligozoospermia carrying ring chromosome 15. To evaluate the chromosome status and fertilization capability, sperm from a patient carrying ring chromosome 15 were injected into enucleated mouse oocytes.

RESULTS

The karyotypes of motile sperm from a patient carrying ring chromosome 15 were normal, and ring chromosome 15 was not observed in the chromosome spread samples of 1PN. In addition, these motile sperm retained the fertilization capability. However, the fertilization rates decreased (85.2, 76.2, and 64.3%, respectively) along with the decline of the aspect ratio of the sperm head (≥ 1.50, 1.30-1.49, and < 1.30, respectively).

CONCLUSIONS

The karyotypes were normal without ring chromosome 15, and motile sperm with a high aspect ratio showed adequate potential for fertilization.

Molecular characterization and evaluation of complex rearrangements in a case of ring chromosome 15

Background

Ring chromosome 15 is a rare genetic entity. Only a few cases have been reported with characterization using molecular techniques. The clinical presentation is quite variable, as a result of differences in the breakpoints, haploinsufficiency of genes involved in deleted segment/s, level of mosaicism and ring instability resulting in a variability of rearrangement of genetic material.

Case presentation

The proband, a 2 months old boy, presented with small head size and facial dysmorphism. On examination microcephaly, triangular face, small anterior frontanelle, micrognathia, hypotonia, unilateral simian crease, hypertelorism, umbilical hernia, micropenis with mild phimosis were noted. Karyotype revealed 46,XY,r(15)(p11.2q26). Array-comparative genomic hybridization (aCGH) and targeted gene sequencing for microcephaly was carried out for genotype phenotype correlation. Array-CGH detected a 2.8 Mb terminal deletion at 15q26.3 along with a 496 kb interstitial micro-duplication, encompassing the IGF1R gene, in the affected genomic region, which was otherwise missed on conventional karyotype.

Conclusion

The present study highlights the importance of aCGH in not only delineating specific phenotypes through accurate genotypic correlation but also in detection and evaluation of ring chromosome with unexpected complex rearrangements.

Electronic supplementary material

The online version of this article (10.1186/s13039-017-0339-z) contains supplementary material, which is available to authorized users.

Chromosome 15 structural abnormalities: effect on IGF1R gene expression and function

Insulin-like growth factor 1 receptor (IGF1R), mapping on the 15q26.3 chromosome, is required for normal embryonic and postnatal growth. The aim of the present study was to evaluate the IGF1R gene expression and function in three unrelated patients with chromosome 15 structural abnormalities. We report two male patients with the smallest 15q26.3 chromosome duplication described so far, and a female patient with ring chromosome 15 syndrome. Patient one, with a 568 kb pure duplication, had overgrowth, developmental delay, mental and psychomotor retardation, obesity, cryptorchidism, borderline low testis volume, severe oligoasthenoteratozoospermia and gynecomastia. We found a 1.8-fold increase in the IGF1R mRNA and a 1.3-fold increase in the IGF1R protein expression (P < 0.05). Patient two, with a 650 kb impure duplication, showed overgrowth, developmental delay, mild mental retardation, precocious puberty, low testicular volume and severe oligoasthenoteratozoospermia. The IGF1R mRNA and protein expression was similar to that of the control. Patient three, with a 46,XX r(15) (p10q26.2) karyotype, displayed intrauterine growth retardation, developmental delay, mental and psychomotor retardation. We found a <0.5-fold decrease in the IGF1R mRNA expression and an undetectable IGF1R activity. After reviewing the previously 96 published cases of chromosome 15q duplication, we found that neurological disorders, congenital cardiac defects, typical facial traits and gonadal abnormalities are the prominent features in patients with chromosome 15q duplication. Interestingly, patients with 15q deletion syndrome display similar features. We speculate that both the increased and decreased IGF1R gene expression may play a role in the etiology of neurological and gonadal disorders.

Pre- and Postnatal Analysis of Chromosome 15q26.1 and 8p23.1 Deletions in Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) is defined as a protrusion of abdominal content into the thoracic cavity through an abnormal opening in the diaphragm present at birth. It is a common birth defect with high mortality and morbidity. Submicroscopic deletions of 15q26.1 and 8p23.1 have been reported in several cases of CDH. We studied a total of 17 cases with CDH in pre- and postnatal samples using FISH probes. Deletion 15q26.1 was seen in 1/17 prenatal samples. There was no deletion for 8p23.1 in all the samples analyzed. CDH has a genetic etiology, and deletion 15q26.1 increases the risk of CDH. Deletion 15q26.1 in a fetus with CDH is a predictor of poor prognosis. This deletion is also seen in a phenotype similar to Fryns syndrome. CDH identified pre- or postnatally should be investigated further to exclude a 15q26.1 deletion and enable appropriate parental counseling.

Autosomal ring chromosomes in human genetic disorders

Ring chromosomes arise following breakage and rejoining in both chromosome arms. They are heterogeneous with variable size and genetic content and can originate from any chromosome. Phenotypes associated with ring chromosomes are highly variable as apart from any deletion caused by ring formation, imbalances from ring instability can also occur. Of interest is ring chromosome 20 which has a significant association with epilepsy with seizure onset in early childhood. Severe growth deficiency without major malformations is a common finding in the ring chromosome carrier. This phenotype associated with ring behaviour and mitotic instability and independent of the chromosome involved has been termed the "ring syndrome". Precise genotype-phenotype correlations for ring chromosomes may not be possible as influencing factors vary depending on the extent of deletion in ring formation, ring instability and the level of mosaicism. Although ring chromosomes usually arise as de novo events, familial transmission of rings from carrier to offspring has been described and prenatal diagnosis for any pregnancies should always be considered.

Prenatal diagnosis of a fetus with ring chromosomal 15 by two- and three-dimensional ultrasonography

We report on a prenatal diagnosis of ring chromosome 15 in a fetus with left congenital diaphragmatic hernia (CDH) and severe intrauterine growth restriction (IUGR). A 31-year-old woman, gravida 2 para 1, was referred because of increased nuchal translucency at gestational age of 13 weeks. Comprehensive fetal ultrasound examination was performed at 19 weeks revealing an early onset IUGR, left CDH with liver herniation, and hypoplastic nasal bone. Three-dimensional ultrasound (rendering mode) showed low set ears and depressed nasal bridge. Amniocentesis was performed with a result of a 46,XX,r(15) fetus after a cytogenetic study. A 1,430 g infant (less than third percentile) was born at 36 weeks. The infant presented with respiratory failure and died at 2 h of life. Postnatal karyotype from the umbilical cord confirmed the diagnosis of 15-ring chromosome. We described the main prenatal 2D- and 3D-ultrasound findings associated with ring chromosome 15. The interest in reporting the present case is that CDH can be associated with the diagnosis of 15-ring chromosome because the critical location of the normal diaphragm development is at chromosome 15q26.1-q26.2.

Ophthalmic treatment and vision care of a patient with rare ring chromosome 15: a case report

The Aim. Ring chromosome 15 is a very rare genetic abnormality with a wide spectrum of clinical findings. Up to date, about 50 cases have been documented, whereas no reports on ophthalmological treatment of such patients have been published. The aim of this study is not only to describe a new patient, but also, for the first time, to present the results of nonoperative management of divergent strabismus. Material and Methods. We present an amblyopic patient with 46,XX, r(15) karyotype: treated conservatively for exotropia of 60 prism diopters. The management consisted of refractive and prismatic correction, eye occlusion, and orthoptic exercises between the age of 15 months and 8 years. Results. The deviation angle of exotropia was decreased to 10 prism diopters, the visual acuity improved to 1.0 in both eyes (Snellen chart) and the fixation pattern was normal. The prisms enabled permanent symmetrical stimulation of the retina, which lead to a development of normal single binocular vision (Maddox test, filter test, and synoptophore tests). Conclusions. Parental karyotype was normal; the analysis of a three-generation pedigree has shown no genetic abnormalities or pregnancy losses so the child's karyotype anomaly was classified as de novo that is a single occurrence of this type of chromosomal disorder in this family. Strabismus in ring chromosome 15 patients is a difficult condition to manage, although success may be achieved.

[Deletion 15q26 syndrome]

The association of short stature, microcephaly, congenital cardiac anomaly and intellectual deficit should always raise the suspicion of chromosomal etiology. If G-banded karyotyping fails to detect large chromosomal aberrations, array comparative genomic hybridization (array CGH) should be performed to screen for submicroscopic pathological copy number changes. The authors present a six-year-old girl whose symptoms arose from a 4.1 Mb loss in the 15q26.2-26.3 telomeric region. The syndrome is characterized by a resistance to the insulin-like growth factor 1 - in our case the increased level of the insulin-like growth factor 1 together with the persistent longitudinal growth failure was an important finding and differential diagnostic feature. A brief overview of the literature is provided.

Cutis tricolor parvimaculata in two patients with ring chromosome 15 syndrome

Two unrelated girls presented with multiple disseminated, paired, small café-au-lait spots and hypopigmented macules, suggesting didymosis (twin spotting). The girls also had growth retardation, microcephaly, hypertelorism, triangular facies, and a 46,XY, r(15) karyotype. The term cutis tricolor parvimaculata has been proposed to describe a twin spot phenomenon characterized by small, paired hypochromic and hyperchromic macules on a background of normal intermediate-pigmented skin. It has been hypothesized that the underlying gene locus of this phenomenon is a hot spot for postzygotic recombination, resulting in multiple pigmentary twin spots. Future clinical research may show whether analogous "simple" twin-spot phenotypes in the form of cutis tricolor parvimaculata may be considered a further cutaneous sign of the ring chromosome 15 syndrome.

Drayer's syndrome of mental retardation, microcephaly, short stature and absent phalanges is caused by a recurrent deletion of chromosome 15(q26.2-->qter)

We reevaluated a unique family with two sibs who had a presumed autosomal recessively inherited syndrome characterized by mental retardation, microcephaly, short stature and absent phalanges. This family was originally described by Drayer et al. in 1977. Using modern molecular techniques, we demonstrated that the syndrome is caused by the recurrence of an apparently de novo 15qter deletion of 5.8 Mb. Analysis of polymorphic markers revealed that the deletion was of maternal origin in both cases, indicating germline mosaicism in the clinically unaffected mother. This study demonstrates the possibility of parental mosaicism and the risk of recurrence in sibs for terminal subtelomeric deletions.

Characterization of a cryptic 3.3 Mb deletion in a patient with a "balanced t(15;22) translocation" using high density oligo array CGH and gene expression arrays

Patients with an apparently balanced translocation and an abnormal phenotype may carry a cryptic deletion/duplication at their translocation breakpoints that may explain their abnormalities. Using microarray CGH (aCGH) and gene expression arrays we studied a child with t(15;22)(q26.1;q11.2), developmental delay and mild dysmorphic features. A high density aCGH study with 244,000 oligo probes demonstrated a 3.3 Mb deletion immediately adjacent to the 15q breakpoint. Gene expression studies with 44,000 oligos displayed an approximately 50% reduction of the expression of IGF1R gene that was translocated to the der(22). There are 18 known or hypothetical protein coding genes within the deleted region according to UniProt, RefSeq, and GenBank mRNA (UCSC HG17, May 2004). Although two of these genes, RGMA and ST8SIA2, play an important role in neural development, the mild phenotype of our patient indicates that loss of one copy of these genes may not be critical developmentally. The 50% reduction of IGF1R expression could be responsible for the growth deficiency in the patient. Reviewing the few 15q26 microdeletion cases that have been characterized by aCGH, we discovered that deletion of the segment including distal 15q26.2 to the proximal part of 15q26.3 is associated with severe phenotypes. Our experience demonstrates that high-density oligonucleotide-based aCGH is a quick and precise way to identify cryptic copy number changes in "balanced translocations." Expression studies can also add valuable information regarding gene expression changes due to a chromosomal rearrangement. Both approaches can assist in the elucidation of the etiology of unexplained phenotypic differences in cases such as this one.

Methylation-specific multiplex ligation-dependent probe amplification analysis of subjects with chromosome 15 abnormalities

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are neurodevelopmental disorders caused by loss of expression of imprinted genes from the 15q11-q13 region. They arise from similar defects in the region but differ in parent of origin. There are two recognized typical 15q11-q13 deletions depending on size and several diagnostic assays are available but each has limitations. We evaluated the usefulness of a methylation-specific multiplex ligation-dependent probe amplification (MLPA) kit consisting of 43 probes to detect copy number changes and methylation status in the region. We used the MLPA kit to genotype 82 subjects with chromosome 15 abnormalities (62 PWS, 10 AS and 10 individuals with other chromosome 15 abnormalities) and 13 with normal cytogenetic findings. We developed an algorithm for MLPA probe analysis which correctly identified methylation abnormalities associated with PWS and AS and accurately determined copy number in previously assigned genetic subtypes including microdeletions of the imprinting center. Furthermore, MLPA analysis identified copy number changes in those with distal 15q deletions and ring 15s. MLPA is a relatively simple, cost-effective technique found to be useful and accurate for methylation status, copy number and analysis of genetic subtype in PWS and AS, as well as other chromosome 15 abnormalities.

Monosomy and trisomy of 15q24-qter with cleft lip and palate

Chromosome 15 aberrations clinically present as facial dysmorphisms such as a prominent nose, low-set ears, micrognathia and a short neck; a cleft lip and palate have not been reported. This is the first reported case of de-novo terminal deletion at 15q24 with a cleft lip and palate and low-set ears. The baby boy had a complete cleft lip and palate on the left side and incomplete cleft lip and palate on the right. A chromosomal study revealed partial monosomy and trisomy of the long arm of chromosome 15, with a karyotype of 46,XY,add(15)(24q) de novo. Surgery for lip plasty was performed at 6 months old and for palate plasty at 1 year and 9 months. Both operations were uneventful, although preoperative and postoperative examinations showed high creatinine phosphokinase values. At 3 years old, mild mental retardation was observed, but his physical development was normal.

Ring chromosome 12 and severe oligospermia: a case report

OBJECTIVE

To describe an unusual presentation of ring chromosome 12, which manifested as severe azoospermia, resulting in male infertility.

DESIGN

Case report.

SETTING

In vitro fertilization center at a tertiary care hospital.

PATIENT(S)

A 27-year-old man diagnosed with unexplained azoospermia and ring chromosome 12 abnormality during a workup for primary infertility.

INTERVENTION(S)

In vitro fertilization with preimplantation genetic diagnosis.

MAIN OUTCOME MEASURE(S)

To confirm the importance of obtaining karyotypes in individuals with severe oligospermia.

RESULT(S)

Full-term pregnancy after IVF using donor sperm.

CONCLUSION(S)

Severe oligospermia and male infertility should be included in the spectrum of findings found in ring chromosome 12.

De novo subtelomeric deletion of 15q associated with satellite translocation in a child with developmental delay and severe growth retardation

We report on a case of satellited 15q with subtelomeric deletion in a girl with delayed development and severe growth retardation. The patient also has a triangular face, downturned angles of the mouth, micrognathia, and minor limb malformations including mild talipes equinovarus, genu recurvatum, and increased dorsiflexion of both limbs. Cytogenetic analysis using standard GTG banding showed a female karyotype with a satellited-like structure at the distal long arm of one chromosome 15. Silver staining of the nucleolar organizing region (AgNOR) confirmed the presence of a satellite DNA translocation at the lesion. Analysis using fluorescent in situ hybridization (FISH) detected a subtelomeric deletion of the terminal 15q. Additional molecular analysis using microsatellite markers along the long arm of chromosome 15 defined a maximally deleted region at approximately 4.7 Mb. Haploinsufficiency of the IGF1R gene expression is thought to be the cause of growth delay in all 15q terminal deletion including our patient.

Ring chromosome 15: characterization by array CGH

Ring chromosome 15 [r(15)] is an uncommon finding with less than 50 patients reported. Precise genotype-phenotype correlations are problematic because of the difficulties in determining the extent of euchromatic loss, the level of mosaicism, and the influence of the timing of ascertainment. We report two discordant examples of r(15) patients. In the first case, prenatal diagnosis of a de novo r(15) was made during the second trimester: mos 46,XX,r(15)(p11.2q26)[32]/45,XX,-15[13]/47,XX,r(15)(p11.2q26)x2[3]/46,XX,dic r(15)(p11.2q26p11.2q26[1]/46,XX[2]. Postnatal follow-up revealed extremely small stature, heart defects, and developmental delay. Patient 2 was a 31-year-old short-statured female who was living independently: 46,XX,r(15)(p11q26). Both cases showed loss of the 15q subtelomeric region by fluorescence in situ hybridization (FISH). To investigate the discordance in phenotypes between the two patients, we undertook array comparative genomic hybridization (array CGH) analyses to more fully characterize the deletions associated with these otherwise structurally indistinguishable r(15) chromosomes from conventional cytogenetic analyses and fluorescence in situ hybridization (FISH) studies. By array CGH, patient 1 showed deletion of multiple contiguous clones predicting an approximately 6 Mb deletion of distal 15q. In contrast, patient 2 showed loss of just the 15q subtelomeric clone and an interstitial clone by array CGH confirming that the severity of the phenotype correlated with the size of the deletion at the molecular level. These cases illustrate the utility of array CGH characterization for determining the size of the associated deletion in ring chromosomes and for facilitating phenotype-genotype correlations.

Detection of an unexpected subtelomeric 15q26.2 --> qter deletion in a little girl: clinical and cytogenetic studies

Unlike the small proximal 15q deletions causing Prader-Willi and/or Angelman syndrome, distal deletions of the terminal long arm of chromosome 15 have rarely been described. To the best of our knowledge, only four patients with a pure terminal 15q deletion have been documented in the literature. We report here on an unexpected abnormal hybridization pattern for the 15q specific subtelomeric control probe (clone 154P1) of the commercial SNRPN probe in a girl referred for suspicion of Angelman syndrome. Investigation by fluorescent in situ hybridization (FISH) using bacterial artificial chromosome (BAC) clones defined a partial monosomy 15q26.2 --> 15qter for a minimal critical region of approximately 5.7 Mb, which is the most distal de novo 15qter deletion reported to date. All the de novo 15qter deletion cases, including ours, presented with pre- and post-natal growth retardation related to the loss of one copy of the IGF1R gene. Based on the comparaison with the previous published cases and owing to the clinical phenotype of our patient, we define a new subtelomeric 15qter syndrome which would be characterized by intrauterine growth retardation and global post-natal growth failure, variable mental retardation, facial anomalies including relative micrognathia and triangular facies and minor malformations of the extremities including proximally placed thumbs, cubitus valgus, and brachydactyly with tappering of the digits.

Terminal deletion of chromosome 15q26.1: case report and brief literature review

Terminal deletions of chromosome 15q are rare events, with only six cases previously described. Here we describe a seventh case of a terminal deletion of the long arm of chromosome 15, with the present case exhibiting clinical features not previously described.

Congenital diaphragmatic hernia and chromosome 15q26: determination of a candidate region by use of fluorescent in situ hybridization and array-based comparative genomic hybridization

Congenital diaphragmatic hernia (CDH) has an incidence of 1 in 3,000 births and a high mortality rate (33%-58%). Multifactorial inheritance, teratogenic agents, and genetic abnormalities have all been suggested as possible etiologic factors. To define candidate regions for CDH, we analyzed cytogenetic data collected on 200 CDH cases, of which 7% and 5% showed numerical and structural abnormalities, respectively. This study focused on the most frequent structural anomaly found: a deletion on chromosome 15q. We analyzed material from three of our patients and from four previously published patients with CDH and a 15q deletion. By using array-based comparative genomic hybridization and fluorescent in situ hybridization to determine the boundaries of the deletions and by including data from two individuals with terminal 15q deletions but without CDH, we were able to exclude a substantial portion of the telomeric region from the genetic etiology of this disorder. Moreover, one patient with CDH harbored a small interstitial deletion. Together, these findings allowed us to define a minimal deletion region of approximately 5 Mb at chromosome 15q26.1-26.2. The region contains four known genes, of which two--NR2F2 and CHD2--are particularly intriguing gene candidates for CDH.

Molecular cytogenetic characterization of ring chromosome 15 in three unrelated patients

We report molecular cytogenetic characterization of ring chromosome 15 in three unrelated male patients with the karyotype 46,XY,r(15). One was a stillborn child with several malformations, and the other two cases showed pre- and postnatal growth retardation and developmental delay, common features for ring chromosome 15 syndrome. One of these patients also displayed clinical features resembling Prader-Willi syndrome (PWS). To delineate the extent of the deletion on chromosome 15, we have carried out fluorescence in situ hybridization (FISH) using bacterial artificial chromosomes (BACs) mapping to the distal long arm of chromosome 15. The deletion breakpoints clustered within a 4.5-6.5 Mb region proximal to the 15q telomere. Two deletions involved the same known genes, while the largest deletion observed in the stillborn child involved three additional genes, including the COUP-TFII gene, which has been suggested to play a role in heart development. The heart malformations, which are observed in this patient, are thus likely to be due to hemizygosity/haploinsufficiency of the COUP-TFII gene. In all three patients, the insulin-like growth factor I receptor gene (IGF1R) gene was deleted supporting the association between IGF1R and growth retardation seen in ring chromosome 15 syndrome.

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.

Postnatal overgrowth by 15q-trisomy and intrauterine growth retardation by 15q-monosomy due to familial translocation t(13;15): dosage effect of IGF1R?

We report a 4-year-old boy, a 6-month-old girl, and a 17-week-old fetus all with a chromosomal imbalance derived from a balanced translocation t(13;15)(q34;q26.1) of their father. The boy had a partial trisomy for 15q26.1-qter (46,XY,der(13)t(13;15)(q34;q26.1)) and postnatal overgrowth, as well as craniosynostosis, facial anomalies, and finger joint contractures, while the girl with the same chromosomal aberration did not show overgrowth, although she had similar craniofacial and skeletal abnormalities. The fetus had a partial monosomy for 15q26.1-qter and intrauterine growth retardation (IUGR). Fluorescence in situ hybridization (FISH) analysis with a BAC clone covering the insulin-like growth factor 1 receptor gene (IGF1R) that is located to 15q25-q26 revealed three copies in the boy, one copy in the fetus, and two copies in their phenotypically normal father. Since deletion of IGF1Rhas repeatedly been reported to be associated with IUGR, it is tempting to speculate that the dosage of IGF1R may have determined growth in these children.

Silver-Russell syndrome: a dissection of the genetic aetiology and candidate chromosomal regions

The main features of Silver-Russell syndrome (SRS) are pre- and postnatal growth restriction and a characteristic small, triangular face. SRS is also accompanied by other dysmorphic features including fifth finger clinodactyly and skeletal asymmetry. The disorder is clinically and genetically heterogeneous, and various modes of inheritance and abnormalities involving chromosomes 7, 8, 15, 17, and 18 have been associated with SRS and SRS-like cases. However, only chromosomes 7 and 17 have been consistently implicated in patients with a strict clinical diagnosis of SRS. Two cases of balanced translocations with breakpoints in 17q23.3-q25 and two cases with a hemizygous deletion of the chorionic somatomammatropin gene (CSH1) on 17q24.1 have been associated with SRS, strongly implicating this region. Maternal uniparental disomy for chromosome 7 (mUPD(7)) occurs in up to 10% of SRS patients, with disruption of genomic imprinting underlying the disease status in these cases. Recently, two SRS patients with a maternal duplication of 7p11.2-p13, and a single proband with segmental mUPD for the region 7q31-qter, were described. These key patients define two separate candidate regions for SRS on both the p and q arms of chromosome 7. Both the 7p11.2-p13 and 7q31-qter regions are subject to genomic imprinting and the homologous regions in the mouse are associated with imprinted growth phenotypes. This review provides an overview of the genetics of SRS, and focuses on the newly defined candidate regions on chromosome 7. The analyses of imprinted candidate genes within 7p11.2-p13 and 7q31-qter, and gene candidates on distal 17q, are discussed.

Increased fetal nuchal fold leading to prenatal diagnosis of ring chromosome 15

We report on the prenatal diagnosis of ring chromosome 15 in a fetus with increased nuchal fold and intrauterine growth restriction (IUGR). A 27-year-old woman gravida 2, para 1 had normal maternal serum screen tests in the early second trimester of the index pregnancy. Fetal nuchal fold thickening up to 8 mm was incidentally found during the routine obstetric ultrasound scan at 20 weeks' gestation. Amniocentesis was undertaken and the fetal karyotype was found to be 46,XY,r(15) on cytogenetic study. Fluorescence in situ hybridization (FISH) using a telomeric probe of chromosome 15 demonstrated a terminal deletion on the q arm of the ring-shaped chromosome 15. This is the first report of a prenatally diagnosed case of ring chromosome 15. Moreover, nuchal fold thickness in the second trimester may have a role in its prenatal diagnosis.

Imprinting of human GRB10 and its mutations in two patients with Russell-Silver syndrome

Documentation of maternal uniparental disomy of chromosome 7 in 10% of patients with Russell-Silver syndrome (RSS), characterized by prenatal and postnatal growth retardation and dysmorphic features, has suggested the presence of an imprinted gene on chromosome 7 whose mutation is responsible for the RSS phenotype. Human GRB10 on chromosome 7, a homologue of the mouse imprinted gene Grb10, is a candidate, because GRB10 has a suppressive effect on growth, through its interaction with either the IGF-I receptor or the GH receptor, and two patients with RSS were shown to have a maternally derived duplication of 7p11-p13, encompassing GRB10. In the present study, we first demonstrated that the GRB10 gene is also monoallelically expressed in human fetal brain tissues and is transcribed from the maternally derived allele in somatic-cell hybrids. Hence, human GRB10 is imprinted. A mutation analysis of GRB10 in 58 unrelated patients with RSS identified, within the N-terminal domain of the protein, a P95S substitution in two patients with RSS. In these two cases, the mutant allele was inherited from the mother. The fact that monoallelic GRB10 expression was observed from the maternal allele in this study suggests but does not prove that these maternally transmitted mutant alleles contribute to the RSS phenotype.

In vitro and in vivo responses to short-term recombinant human insulin-like growth factor-1 (IGF-I) in a severely growth-retarded girl with ring chromosome 15 and deletion of a single allele for the type 1 IGF receptor gene

OBJECTIVES

Patients with single allele defects in the gene encoding the type 1 IGF receptor have been reported to have growth failure, but fibroblasts from affected patients have not exhibited insensitivity to the effects of IGF-I in vitro. The in vitro and in vivo responses to short-term recombinant human IGF-I (rhIGF-I) in a severely growth-retarded girl with ring chromosome 15 and deletion of a single allele for the type 1 IGF receptor gene have been investigated.

DESIGN AND PATIENT

The child exhibited prenatal and severe post-natal growth failure, and delayed psychomotor development. Southern blotting revealed a 50% reduction in IGF-I receptor DNA, and in an RNase protection assay (RPA), a quantitatively similar reduction in steady-state mRNA for type 1 IGF receptor. rhIGF-I was administered in graded doses of 40, 60 and 80 microg/kg twice daily by subcutaneous injection for periods of 2-2.5 days each.

RESULTS

During rhIGF-I treatment, mean urinary nitrogen excretion was unchanged and urinary calcium rose to 60% greater than in the pre-treatment period. rhIGF-I injections produced only a modest decrease in indices of GH secretion, assessed by frequent (every 20 min) sampling over periods of 12 h. There was no significant difference between the mean GH concentrations during rhIGF-I treatment (5.32 +/- 6.2 mU/l) compared with that before rhIGF-I treatment (8.46 +/- 10.2 mU/l). Mean IGFBP-3-values were increased (4.5 mg/l before vs. 5.4 mg/l during rhIGF-I). TSH values after injection of TRH were not significantly reduced by IGF-I (mean of all values, 18.6 mU/l vs. 15.5 mU/l during rhIGF-I treatment). In vitro binding of radiolabelled IGF-I to the patient's fibroblasts was less than that bound by control fibroblasts (patient, 0.69% binding by 248 000 cells, vs. 1.41% binding by 260 000 fibroblasts from an age-matched control). However, the patient's fibroblasts exhibited a growth response in vitro to the addition of IGF-I in a fashion similar to that of control fibroblasts.

CONCLUSIONS

These studies show evidence in each of the indices examined of in vivo resistance to IGF-I and suggest that the growth retardation observed in such patients may be the direct result of the absence of one of the alleles encoding the type 1 IGF receptor.

The diagnostic value of café-au-lait macules

Single café-au-lait macules (CALMs) are common in the pediatric population and in most children represent a normal finding. It is important to recognize whether the presence of multiple CALMs in a particular patient is normal or indicates an association with a multisystem disorder. This article addresses issues concerning the prevalence, genetics, and natural history of CALMs in the general population and reviews disorders in which CALMs are present as a characteristic trait.

Analysis of imprinted genes in subjects with Prader-Willi syndrome and chromosome 15 abnormalities

PURPOSE

To determine gene expression of five imprinted genes or transcripts from the 15q11-q13 chromosome region using reverse transcription polymerase chain reaction (RT-PCR) in a relatively large survey of Prader-Willi syndrome (PWS) and control subjects with several different chromosome 15 abnormalities.

METHODS

RT-PCR was undertaken on mRNA isolated from tissue (e.g., mostly lymphoblasts) from 38 PWS and 10 control subjects. DNA primers were used for five imprinted genes or transcripts (ZNF127, SNRPN, PAR5, IPW, and PAR1) from 15q11-q13 and fibrillin, a control gene from 15q21.

RESULTS

One PWS subject with maternal disomy 15 showed weak but detectable expression of PAR1, whereas SNRPN expression was detected in two PWS subjects [one with the 15q11-q13 deletion and one with a t(15;15) karyotype and maternal disomy 15], and the remaining typical PWS subjects showed no expression of the imprinted genes or transcripts.

CONCLUSION

No obvious clinical differences were identified in those PWS subjects with weak expression of genes compared with those showing no expression. Although the reason(s) for weak expression is unknown, possible explanations include relaxation of imprinting caused by failure to reset the imprinted genes or transcripts in the maternal germ line or by postzygotic gene expression or undetected chromosome 15 mosaicism in the deletion PWS subjects. The timing, tissue source, and other factors relating to partial expression of genes that are thought to be imprinted may play a role in clinical variability and allow for a better understanding of molecular mechanisms in PWS and other abnormalities of proximal chromosome 15q.

Congenital scoliosis (hemivertebra) associated with de novo balanced reciprocal translocation, 46,XX,t(13;17)(q34;p11.2)

We report on an 8-year-old girl with congenital scoliosis (segmented hemivertebra between the second and third lumbar vertebrae) and psychomotor developmental delay. She has a de novo reciprocal translocation, t(13;17)(q34;p11.2). Congenital scoliosis is one type of structural spine deformation and hemivertebra is the most common anomaly causing congenital scoliosis. The cause and the mode of inheritance of hemivertebrae are unknown. Our patient has a de novo balanced chromosome aberration and retains two copies of the LLGL gene, which is usually lacking in patients with Smith-Magenis syndrome (SMS). Since some SMS patients who showed a deletion at 17p11.2 had congenital scoliosis, it is likely that one (17p11.2) of the breakpoints in our patient is a candidate region for a hemivertebra locus.

Brachydactyly in a child with duplication-deficiency subsequent to t(15;20)(q25.2;p12.2)mat. Candidate regions on one or both chromosomes?

We report a child with a duplication-deficiency subsequent to t(15;20)(q25.2;p12.2), transmitted in at least 5 generations, who showed features of 15q- syndrome. We speculate that brachydactyly--most likely because of brachymesophalangism--is a feature of the phenotype of this chromosomal aberration and points to candidate gene(s) in this region. A similar brachydactyly was, however, reported with dup(20p1-pter).

Distinct 15q genotypes in Russell-Silver and ring 15 syndromes

Individuals with a ring 15 chromosome [r(15)] and those with Russell-Silver syndrome have short stature, developmental delay, triangular face, and clinodactyly. To assess whether the apparent phenotypic overlap of these conditions reflects a common genetic cause, the extent of deletions in chromosome 15q was determined in 5 patients with r(15), 1 patient with del 15q26.1-qter, and 5 patients with Russell-Silver syndrome. All patients with Russell-Silver syndrome were diploid for genetic markers in distal 15q, indicating that Russell-Silver syndrome in these individuals was unlikely to be related to the expression of single alleles at these or linked genetic loci. At least 3 distinct sites of chromosome breakage close to the telomere were found in the r(15) and del 15q25.1-qter patients, with 1 r(15) patient having both a terminal and an interstitial deletion. Although the patient with del 15q25.1-qter exhibited the largest deletion and the most profound growth retardation, the degree of growth impairment among the r(15) patients was not correlated with the size of the deleted interval. Rather, the parental origin of the ring chromosome in several patients was associated with phenotypes that are also seen in patients with either Prader-Willi (PWS) or Angelman (AS) syndromes, conditions that result from uniparental expression of genes on chromosome 15. In fact, unequal representation of chromosome 15 alleles in 1 patient with r(15) suggests the possibility that a mosaic karyotype composed of the constitutional cell line and cell line(s) possibly deficient in the ring chromosome might be present. The PWS-like or AS-like phenotypes could be explained by postzygotic loss of the ring chromosome, leading to uniparental inheritance of the intact chromosome in some tissues of r(15) patients.

Good growth response to growth hormone treatment in the ring chromosome 15 syndrome

Ring chromosome 15 syndrome is a rare condition in which severe growth retardation is a major finding. We report a 4 year old boy with the karyotype 46,XY, r(15)(p11.2q26.2) whom we have treated with recombinant human growth hormone (GH) for two years. During the first year of treatment, the insulin-like growth factor I increased from subnormal 4.2 nmol/l to normal 13.8 nmol/l and the insulin-like growth factor binding protein 3 levels increased from 2.6 to 3.8 mg/l, whereas high binding protein 1 concentrations normalised from 52.0 to 16.7 micrograms/l. During the two years of treatment his relative height improved from -6.2 SD to -4.4 SD and the predicted adult height from 159.6 cm to 163.5 cm. Owing to the good growth response, we have decided to continue GH treatment.

Familial occurrence of ring chromosome 15

We present a family with the ring 15 chromosome (r(15)) syndrome in a 2-year-old infant and his mother. Both had the common clinical manifestations reported in previous cases with r(15), including severe short stature, microcephaly, triangular face, and mild mental retardation. The family also had a normal son. Although males with r(15) syndrome usually seem to be infertile, female r(15) patients are likely to be fertile and their reproductivity may be influenced by severe growth retardation.

An infant with deletion of the distal long arm of chromosome 15 (q26.1----qter) and loss of insulin-like growth factor 1 receptor gene

We report on an infant with a previously undescribed chromosome 15 deletion (q26.1----qter) and compare the clinical findings with those of 7 reported patients with deletions of distal 15q, as well as ring chromosome 15 syndrome patients. Most of the patients with deletions of distal 15q, including our patient, have intrauterine growth retardation (IUGR), microcephaly, abnormal face and ears, micrognathia, highly arched palate, renal abnormalities, lung hypoplasia, failure to thrive, and developmental delay/mental retardation. Several genes have been assigned to the 15q25----qter region, including insulin-like growth factor 1 receptor (IGF1R). DNA analysis from our patient documented the loss of one IGF1R gene copy. Our study further localizes the IGF1R gene distal to the 15q26.1 band. It is interesting to speculate that the severe IUGR and postnatal growth deficiency of our patient and other patients with similar chromosome 15 deletions are related to the loss of an IGF1R gene copy which may lead to an abnormal number and/or structure of the receptors.