Georg Klaus Hinkel

Spectrum of mutations in PTPN11 and genotype-phenotype correlation in 96 patients with Noonan syndrome and five patients with cardio-facio-cutanesous syndrome

Noonan syndrome (NS) is a relatively common, but genetically heterogeneous autosomal dominant malformation syndrome. Characteristic features are proportionate short stature, dysmorphic face, and congenital heart defects. Only recently, a gene involved in NS could be identified. It encodes the non-receptor protein tyrosine phosphatase SHP-2, which is an important molecule in several intracellular signal transduction pathways that control diverse developmental processes, most importantly cardiac semilunar valvulogenesis. We have screened this gene for mutations in 96 familial and sporadic, well-characterised NS patients and identified 15 different missense mutations in a total of 32 patients (33%), including 23 index patients. Most changes clustered in one exon which encodes parts of the N-SH2 domain. Five of the mutations were recurrent. Interestingly, no mutations in the PTPN11 gene were detected in five additional patients with cardio-facio-cutaneous (CFC) syndrome, which shows clinical similarities to NS.

Genotyping in 46 patients with tentative diagnosis of Treacher Collins syndrome revealed unexpected phenotypic variation

To define the range of phenotypic expression in Treacher Collins syndrome (TCS; Franceschetti–Klein syndrome), we performed mutation analysis in the TCOF1 gene in 46 patients with tentative diagnosis of TCS and evaluated the clinical data, including a scoring system. A total of 27 coding exons of TCOF1 and adjacent splice junctions were analysed by direct sequencing. In 36 patients with a clinically unequivocal diagnosis of TCS, we detected 28 pathogenic mutations, including 25 novel alterations. No mutation was identified in the remaining eight patients with unequivocal diagnosis of TCS and 10 further patients, in whom the referring diagnosis of TCS was clinically doubtful. There is no overt genotype–phenotype correlation except that conductive deafness is significantly less frequent in patients with mutations in the 3′ part of the open reading frame. Inter- and intrafamilial variation is wide. Some mutation carriers, parents of typically affected patients, are so mildly affected that the diagnosis might be overlooked clinically. This suggests that modifying factors are important for phenotypic expression. Based on these findings, minimal diagnostic criteria were defined: downward slanting palpebral fissures and hypoplasia of the zygomatic arch. The difficulties in genetic counselling, especially diagnosis of family members with a mild phenotype, are described.

DNA, FISH and complementation studies in ICF syndrome : DNA hypomethylation of repetitive and single copy loci and evidence for a trans acting factor

ICF syndrome (ICFS) is a rare immunodeficiency disorder characterized by instability of the pericentromeric heterochromatin predominantly of chromosomes 1 and 16. DNA methylation studies in two unrelated ICFS patients provide further evidence for a marked hypomethylation of satellite 2 DNA. The ICFS-specific disturbances of chromatin structure take place within the satellite 2 DNA regions, as demonstrated by fluorescence in situ hybridization analysis. Moreover, methylation studies of genomic imprinted loci D15S63, D15S9, and H19 have revealed hypomethylation to different degrees in both patients; this provides evidence for hypomethylation at autosomal single copy loci in ICFS. Cell fusion experiments have revealed a distinct reduction of chromosomal abnormalities in ICFS cells after fusion with normal cells, suggesting that the abnormalities are caused by the loss of function of an as yet unknown trans acting factor. Although it is now clear that wide-spread DNA hypomethylation is a characteristic feature of ICFS, neither the cause and mechanism of hypomethylation nor their relationship to the clinical symptoms is known. We speculate that a phenotypic effect might result from tissue-dependent abnormal gene expression and/or from a possible structural disturbance of DNA domains, which, with respect to the immunodeficiency, partially prevents the normal somatic recombinations in immunologically active cells.

Minimal clinical expression of the holoprosencephaly spectrum and of currarino syndrome due to different cytogenetic rearrangements deleting the Sonic Hedgehog gene and the HLXB9 gene at 7q36.3

We report clinical, cytogenetic, and molecular cytogenetic studies on four patients with subtle or submicroscopic 7q36 deletions either of de novo origin or resulting from a cryptic parental translocation. Fluorescence in situ hybridization (FISH) studies indicated that in all four patients, the Sonic Hedgehog gene (SHH) and the homeobox gene HLXB9, among others, are comprised in the deletions. Besides mental retardation and short stature, all patients showed only minimal manifestations of the holoprosencephaly (HPE) spectrum and only one displayed symptoms of the Currarino syndrome. Patient 1 had a de novo 7q36.1‐qter deletion and showed microcephaly, ptosis, sacral agenesis, tethered cord, but no structural brain anomaly. Patient 2 had a submicroscopic de novo 7q36 deletion detected by FISH, and showed facial and cerebral microsigns of the HPE spectrum. Patient 3 had a 7q36 deletion found by subtelomere FISH testing that was the unbalanced product of a subtle maternal 7q;10q translocation. She presented facial and ocular microsigns, but no structural abnormality of the brain. Patient 4 showed no specific syndromal pattern and was found to have a cryptic unbalanced de novo translocation of the terminal parts of chromosomes 7q and 9p by subtelomere FISH. Patients 2, 3, and 4 represent the first report of a de novo submicroscopic 7q36 deletion, the second report of a familial subtle translocation of 7q36, and the first report of an unbalanced de novo submicroscopic translocation of 7q36, respectively. Our results stress the importance of 7q36 deletion studies by FISH in patients with microsigns of the HPE spectrum.

Body height in Turner's syndrome

Disease‐specific growth curves for Turners syndrome were calculated by means of 2nd order homogeneous differential equations with constant coefficients, taking different cytogenetical subtypes into account. Comparison of these growth curves between X‐monosomic (n=64) and 46,XX/45,X‐mixoploid (n = 20) patients reveals no differences, in contrast to the commonly accepted opinion.

Subtelomere FISH in 50 children with mental retardation and minor anomalies, identified by a checklist, detects 10 rearrangements including a de novo balanced translocation of chromosomes 17p13.3 and 20q13.33.

Submicroscopic or subtle aneusomies at the chromosome ends, typically diagnosed by subtelomere fluorescence in situ hybridization (FISH), are a significant cause of idiopathic mental retardation (MR). Some 20 subtelomere studies, including more than 2,500 subjects, have been reported. The studies are not directly comparable because different techniques and patient ascertainment criteria were used, but an analysis of 14 studies showed that aberrations were detected in 97 out of 1,718 patients (5.8%, range 2–29%; 95% confidence interval (CI) 4.60–6.84%). We performed a subtelomere FISH study of 50 unrelated children ascertained by a checklist that evaluates MR or developmental delay, dysmorphism, growth defect, and abnormal pedigree and found 10 bona fide causal rearrangements (detection rate 20%, 95% CI 10–33.7%). The findings included five unbalanced familial translocations or inversions, two unbalanced de novo translocations, and two de novo deletions. Patient 5 showed multiple anomalies (large head, vision defect, omphalocele, heart defect, enlarged kidneys, moderate MR, speech defect, mild transient homocysteinemia) and a de novo balanced translocation of chromosomes 17p13.3 and 20q13.33. The report of a subtelomeric balanced rearrangement associated with a disease phenotype is a novel one. FISH mapping using panels of overlapping BAC clones identified a number of candidate genes at or near his breakpoints, including ASPA, TRPV3, TRPV1, and CTNS at 17p13.3, and three genes of unknown function at 20q13.33. Only the homocysteinemia could be speculatively linked to one of these genes (CTNS, the gene for cystinosis). Three within the subset of 16 children (18.8%) with mild (IQ, 50–69) or unspecified degree of MR tested positive, suggesting that the checklist approach could be especially useful within this group of patients.

Deletion mapping by FISH with BACs in patients with partial monosomy 22q13

Abstract Patients with deletions in 22q13 are known to have phenotypic features that include normal or accelerated growth, large hands and feet, hypotonia, delayed psychomotor development and mild facial dysmorphism. To date, very few cases have been investigated by detailed molecular genetic analysis. We have analyzed three new patients with terminal deletions in 22q. We compared the cytogenetic observations with molecular data assessed by fluorescence in situ hybridization and an array of characterized bacterial artificial chromosome recombinants. The shortest region of deletion overlap is localized in 22q13.2–qter distal to the marker D22S94, but the telomeric repeat in the deleted chromosome appears to remain intact. When parental alleles were investigated in two of the three patients, the aberrant homolog was found to be of paternal origin in both cases. Although the deleted region still spans >20 cM, molecular analysis of additional patients and screening for new genes might help in elucidating candidate genes connected with the dysmorphisms defined by deletions of 22q13.

Evidence for a critical region for penoscrotal inversion, hypospadias, and imperforate anus within chromosomal region 13q32.2q34

Two unrelated patients with small distal deletions of the long arm of chromosome 13 are described, with shawl scrotum and penoscrotal transposition, penoscrotal hypospadias, a reduced perineum, and anal atresia. The patients have small deletions of 13(q32.2qter) and 13(q32q34), respectively. This report and the literature present evidence for one or possibly more gene(s) within region 13q32.2q34 which regulate the development of the ano-genital structures. The clinical spectrum includes bifid or shawl scrotum, hypospadias, biseptate uterus, malplaced and imperforate anus, and common cloaca.

A small deletion of 16q23.1-->16q24.2 [del(16)(q23.1q24.2).ish del(16)(q23.1q24.2)(D16S395+, D16S348-, P5432+)] in a boy with iris coloboma and minor anomalies.

We report on a 5-year-old boy with bilateral coloboma of iris, short stature, moderate developmental delay, and a few minor craniofacial anomalies. High-resolution GTG banding showed a small distal deletion of one chromosome 16 [del(16)(q23.1q24.2)]. Molecular refinement of the deletion breakpoints yielded that the proximal breakpoint at 16q23.1 is located between loci D16S395 (present) and D16S348 (absent). Comparison with previously published cases of deletion 16q demonstrated that the clinical phenotype is not a recognizable 16q- syndrome and different from the two cases of deletions of 16(q22.1 to q24.1) described by Callen et al. [1993]. Evidently, deletion 16(q23.1q24.2) has a milder phenotypic effect than other interstitial and distal 16q deletions.

A sterile male with 45,X0 and a Y;22 translocation.

SummaryCytogenetic analysis of a 20-year-old sterile male revealed a 45,X0 karyotype with no evidence for Y-chromosomal material on any of the chromosomes analysed by Q-, G- and C-banding. DNA analysis with 17 different Y chromosome-derived probes revealed the presence of Yp DNA sequences in the patients genome. In situ hybridization with the Yp-derived probe pJA36B disclosed a translocation of Y-chromosomal material onto the short arm of a chromosome 22.