Gerhard Binder

Pseudoautosomal deletions encompassing a novel homeobox gene cause growth failure in idiopathic short stature and Turner syndrome

Growth retardation resulting in short stature is a major concern for parents and due to its great variety of causes, a complex diagnostic challenge for clinicians. A major locus involved in linear growth has been implicated within the pseudoautosomal region (PAR1) of the human sex chromosomes. We have determined an interval of 170 kb of DNA within PAR1 which was deleted in 36 individuals with short stature and different rearrangements on Xp22 or Yp11.3. This deletion was not detected in any of the relatives with normal stature or in a further 30 individuals with rearrangements on Xp22 or Yp11.3 with normal height. We have isolated a homeobox-containing gene (SHOX} from this region, which has at least two alternatively spliced forms, encoding proteins with different patterns of expression. We also identified one functionally significant SHOX mutation by screening 91 individuals with idiopathic short stature. Our data suggest an involvement of SHOX in idiopathic growth retardation and in the short stature phenotype of Turner syndrome patients.

A role for helix 3 of the TRβ ligand-binding domain in coactivator recruitment identified by characterization of a third cluster of mutations in resistance to thyroid hormone

Resistance to thyroid hormone (RTH) has hitherto been associated with thyroid hormone β receptor (TRβ) mutations which cluster in two regions (αα 310–353 and αα 429–461) of the hormone‐binding domain and closely approximate the ligand‐binding cavity. Here, we describe a third cluster of RTH mutations extending from αα 234–282 which constitute a third boundary of the ligand pocket. One mutant, T277A, exhibits impaired transactivation which is disproportionate to its mildly reduced ligand affinity (Ka). T3‐dependent recruitment of coactivators (SRC‐1, ACTR) by mutant receptor–RXR heterodimers was reduced in comparison with wild‐type. Cotransfection of SRC‐1 restored transactivation by T277A. In the TRβ crystal structure this helix 3 residue is surface‐exposed and is in close proximity to residues L454 and E457 in helix 12 which are known to be critical for coactivator interaction, suggesting that they all constitute part of a receptor–coactivator interface. The transcriptional function of other mutants (A234T, R243W/Q, A268D, Δ276I, A279V, R282S) in this cluster correlated with their reduced Ka and they inhibited wild‐type TRβ action in a dominant negative manner. DNA binding, heterodimerization and corepressor recruitment were preserved in all mutants, signifying the importance of these attributes for dominant negative activity and correlating with the absence of natural mutations in regions bordering the third cluster which mediate these functions.

Short stature due to SHOX deficiency: genotype, phenotype, and therapy.

SHOX deficiency is a frequent cause of short stature. The short stature homeobox-containing gene resides in the telomeric PAR1 region on the short arm of both sex chromosomes and escapes X inactivation. For this review, abstracts of 207 publications presented by PubMed for the search term ‘SHOX’ were screened. Heterozygote SHOX mutations (80% deletions) were detected in 2–15% of individuals with formerly idiopathic short stature, in 50–90% of individuals with Leri-Weill dyschondrosteosis, and in almost 100% of girls with Turner syndrome. Mutational analysis is primarily performed by MLPA analysis followed by gene sequencing if necessary. SHOX is a nuclear protein that binds to DNA and acts as a transcriptional activator. Orthologs are present in many vertebrates but not in rodents. Gene expression starting as early as 33 days postconception in humans is predominant in the mid portion of the buds and in the first and second pharyngeal arches. In the growth plate, hypertrophic chondrocytes express SHOX where it seems to have antiproliferative potency. The penetrance of SHOX deficiency is high, but its clinical expression is very variable becoming more pronounced with age and being more severe in females. Growth failure starts early during the first years of life and the height deficit present at preschool age seems not to deteriorate further. The mean adult height is –2.2 SDS. Auxological analysis of the body proportions (mesomelia), the presence of minor abnormalities, and the search for subtle radiographic signs are important keys to the diagnosis which has to be confirmed by genetic analysis. The growth-promoting effect of GH therapy approved for individuals with SHOX mutations seems to be equal to the effect seen in Turner syndrome.

The Endocrine Phenotype in Silver-Russell Syndrome Is Defined by the Underlying Epigenetic Alteration

CONTEXT Around 50% of children with Silver-Russell syndrome (SRS) carry a hypomethylation of the imprinting control region 1 at the IGF2/H19 locus on 11p15, the functional significance of which is unknown. OBJECTIVE We aimed to compare the genotype in SRS with the endocrine phenotype. DESIGN The retrospective study included all SRS children who were treated during the last 18 yr at our hospital and for comparison a cohort of GH treated nonsyndromic short children born small for gestational age (SGA). PATIENTS The 61 patients with SRS included were defined by the presence of intrauterine growth retardation, lack of catch-up growth, and at least two of the criteria: typical face, relative macrocephaly, and skeletal asymmetry. Routine karyotype and GH secretion was normal in all children studied. A subgroup of 53 patients was treated with GH. MATERIALS AND METHODS Genomic DNA was available from 44 children. Multiplex ligation probe-dependent amplification analysis was performed to detect hypomethylation at the imprinting control region 1 on 11p15. Uniparental disomy of chromosome 7 (UPD7) was analyzed by short tandem repeats typing. Serum levels of GH, IGF-I, and IGF-binding protein (IGFBP)-3 were measured by RIA. RESULTS Epimutations at 11p15 were found in 19 of 44, UPD7 in five of 44, and small structural aberrations of the short arm of chromosome 11 in two of 44 children. Of 44 cases, 18 were negative for any genetic defect known (41%). The most severe phenotype was found in children with 11p15-SRS. Children with UPD7-SRS had a significantly higher birth length (P < 0.004) but lost height sd score (SDS) postpartum, whereas children with 11p15-SRS showed no change in height SDS. IGF-I and IGFBP-3 serum levels were inadequately high in 11p15-SRS at -0.02 SDS (1.07, sd) and +1.38 SDS (1.01), compared with the low levels in UPD7-SRS and in the cohort of 58 nonsyndromic SGA children (P < 0.0009). During GH therapy, IGFBP-3 serum levels increased above normal values in 11p15-SRS (P < 10(-4)), whereas IGF-I increase was moderate. There was a trend toward more height gain in children with UPD7 than in those with 11p15 epimutation under GH therapy (+2.5 vs. +1.9 height SDS after 3 yr) (P = 0.08). CONCLUSIONS Children with SRS and an 11p15 epimutation have IGFBP-3 excess and show endocrine characteristics suggesting IGF-I insensitivity, whereas children with SRS and UPD7 were not different from nonsyndromic short children born SGA. This phenotype-genotype correlation implicates divergent endocrine mechanisms of growth failure in SRS.

Significance of Basal IGF-I, IGFBP-3 and IGFBP-2 Measurements in the Diagnostics of Short Stature in Children

The role of IGF-I and IGFBP-3 measurements in the diagnostic work-up of short children is established but remains controversial. Little information exists on the value of IGFBP-2 measurements. Based on reference data established in 388 children we have reinvestigated the issue, using data from 392 short children who underwent the same diagnostic procedures between 1987 and 1998 (GHD, n = 187; non-GHD, n = 205, including patients with ISS, n = 76; IUGR, n = 46; and TS, n = 83). In comparing IGF-I, IGFBP-3 and IGFBP-2 serum levels of GHD and ISS children with reference data, we calculated the sensitivity, specificity, efficiency and positive predictive value for the diagnosis of GHD. The overall sensitivity of the parameters was high, the rank order being as follows: IGF-I >IGFBP-3 >IGFBP-2 (75, 67 and 62%, respectively). In contrast, the specificity was relatively low: IGFBP-3 >IGFBP-2 >IGF-I (50, 50 and 32%, respectively). The efficiency and positive predictive value of parameters was in the order of 40, 60 and 70–80%, respectively. In repeated measurements, the recorded basal levels of IGF-I and IGFBP-3 showed an overall narrow range of variation. We conclude that the determination of basal IGF parameters is, together with anthropometry and imaging techniques, an indispensable tool for differentiating between GHD and ISS; and that IGFBP-2 plays an additional role in this process.

Relevance of IGF-I, IGFBP-3, and IGFBP-2 Measurements during GH Treatment of GH-Deficient and Non-GH-Deficient Children and Adolescents

Background: Little information is available on the relevance of parameters representing the insulin-like growth factor (IGF) system with regard to growth hormone (GH) treatment during childhood. In adults, high IGF-I levels were found to be associated with side effects and long-term risks. Aim/Method: Our aim was to monitor the serum levels of IGF-I, IGF-binding protein (IGFBP) 3, and IGFBP-2 during long-term GH treatment of 156 patients with GH deficiency (GHD) and of 153 non-GHD patients. We determined the extent to which the IGF parameters exceed the normal ranges and identified those parameters which are predictive of 1st-year growth. Results: In prepubertal GHD children, the levels of IGF-I, IGFBP-3, and IGF-I/IGFBP-3 exceeded the 95th centile of the reference values for this age group in 2.3, 0.3, and 7.9% of the cases, respectively, whereas in prepubertal non-GHD children, the same parameters exceeded the 95th reference centile in 20.1, 3.5, and 32.2%, respectively. In pubertal GHD children IGF-I, IGFBP-3, and IGF-I/IGFBP-3 levels exceeded the 95th reference centile in 11.1, 1.5, and 15.4%, respectively. In pubertal non-GHD children, these levels also exceeded the 95th centile in 26.7, 7.0, and 41.4%, respectively. In both GHD and non-GHD groups, however, some patients had IGF parameters which were below the reference values. Our analysis showed that, in both groups, in addition to maximum GH, all IGF parameters (IGF-I, IGFBP-3, IGF-I/IGFBP-3 ratio, IGFBP-2 or derivatives) significantly extend the scope of a calculated model for predicting 1st-year height velocity. Conclusion: For reasons of safety and optimization of GH therapy, it is essential to follow up IGF-I, IGFBP-3, and IGFBP-2 levels regularly during childhood.

Silver‐Russell patients showing a broad range of ICR1 and ICR2 hypomethylation in different tissues

Begemann M, Spengler S, Kanber D, Haake A, Baudis M, Leisten I, Binder G, Markus S, Rupprecht T, Segerer H, Fricke‐Otto S, Mühlenberg R, Siebert R, Buiting K, Eggermann T. Silver‐Russell patients showing a broad range of ICR1 and ICR2 hypomethylation in different tissues.

Broad Clinical Spectrum in Silver-Russell Syndrome and Consequences for Genetic Testing in Growth Retardation

OBJECTIVE. Silver-Russell syndrome is a heterogenous disorder characterized by severe intrauterine growth restriction, lack of catch-up after birth, and specific dysmorphisms. In ∼10% of patients, maternal uniparental disomy of chromosome 7 is detectable, but hypomethylation of the imprinting in 11p15 is the major epigenetic disturbance in Silver-Russell syndrome. The use of strict clinical criteria, indeed, results in relatively high detection rates for the 11p15 epimutation, but we feel that the application of a strict clinical scoring system is not useful in clinical workaday life because of the broad clinical spectrum in 11p15 epimutation and maternal uniparental disomy of chromosome 7 carriers. PATIENTS AND METHODS. We report on our experience of molecular testing in 188 patients referred for routine diagnostics of Silver-Russell syndrome and in a group of 20 patients with isolated intrauterine growth restriction/postnatal growth retardation. RESULTS. The molecular genetic results in both groups of data showed that 11p15 epimutation and maternal uniparental disomy of chromosome 7 carriers did not always show the unambiguous Silver-Russell syndrome phenotype. CONCLUSIONS. In addition to patients with the classical Silver-Russell syndrome phenotype fulfilling the Silver-Russell syndrome-specific scores, genetic testing for the 11p15 epimutation and/or maternal uniparental disomy of chromosome 7 should also be considered in case of “Silver-Russell syndrome-like” phenotypes, for example, mild intrauterine growth restriction and postnatal growth retardation associated with a prominent forehead and triangular face or asymmetry as the only clinical signs. In particular, the lack of intrauterine growth restriction in patients with a Silver-Russell syndrome-like phenotype should not automatically result in exclusion from molecular testing.

Silver-Russell syndrome: genetic basis and molecular genetic testing

Imprinted genes with a parent-of-origin specific expression are involved in various aspects of growth that are rooted in the prenatal period. Therefore it is predictable that many of the so far known congenital imprinting disorders (IDs) are clinically characterised by growth disturbances. A noteable imprinting disorder is Silver-Russell syndrome (SRS), a congenital disease characterised by intrauterine and postnatal growth retardation, relative macrocephaly, a typical triangular face, asymmetry and further less characteristic features. However, the clinical spectrum is broad and the clinical diagnosis often subjective. Genetic and epigenetic disturbances can meanwhile be detected in approximately 50% of patients with typical SRS features. Nearly one tenth of patients carry a maternal uniparental disomy of chromosome 7 (UPD(7)mat), more than 38% show a hypomethylation in the imprinting control region 1 in 11p15. More than 1% of patients show (sub)microscopic chromosomal aberrations. Interestingly, in ~7% of 11p15 hypomethylation carriers, demethylation of other imprinted loci can be detected. Clinically, these patients do not differ from those with isolated 11p15 hypomethylation whereas the UPD(7)mat patients generally show a milder phenotype. However, an unambiguous (epi)genotype-phenotype correlation can not be delineated.We therefore suggest a diagnostic algorithm focused on the 11p15 hypomethylation, UPD(7)mat and cryptic chromosomal imbalances for patients with typical SRS phenotype, but also with milder clinical signs only reminiscent for the disease.

Height Gains in Response to Growth Hormone Treatment to Final Height Are Similar in Patients with SHOX Deficiency and Turner Syndrome

Background: Patients with mutations or deletions of the Short Stature Homeobox-containing(SHOX) gene have variable degrees of growth impairment, with or without mesomelic skeletal dysplasia. If untreated, short patients with SHOX deficiency remain short in adulthood. Growth hormone (GH) treatment improves short-term linear growth; however, there are no data on GH treatment effects on final height. Patients: In a retrospective study, we assessed the relative effects of GH on final height gain in patients with SHOX deficiency (n = 14; 12 females) and Turner syndrome (TS) (n = 158). Patients were included if they fulfilled the following criteria: genetically-confirmed SHOX deficiency or TS, baseline height SDS <1.5, GH treatment started at Tanner stage ≤2, duration of GH treatment >2 years, and final height attained. Results: Both groups of patients were short at baseline (height SDS [mean ± SD]: SHOX deficiency, –3.3 ± 0.9; TS, –2.9 ± 0.8). Height SDS gain from baseline to final height was significant for each patient group (SHOX deficiency, 1.1 ± 0.7; TS, 1.2 ± 0.8; p < 0.001); however, it was not significantly different between groups (p = 0.708). Conclusions: Patients with SHOX deficiency receive similar final height benefit from GH treatment to those with TS.