Joke B. G. M. Verheij

Mutations in CCBE1 cause generalized lymph vessel dysplasia in humans

Lymphedema, lymphangiectasias, mental retardation and unusual facial characteristics define the autosomal recessive Hennekam syndrome. Homozygosity mapping identified a critical chromosomal region containing CCBE1, the human ortholog of a gene essential for lymphangiogenesis in zebrafish. Homozygous and compound heterozygous mutations in seven subjects paired with functional analysis in a zebrafish model identify CCBE1 as one of few genes causing primary generalized lymph-vessel dysplasia in humans.

Familial CHARGE syndrome and the CHD7 gene: a recurrent missense mutation, intrafamilial recurrence and variability.

CHARGE syndrome is an autosomal dominant condition that is caused by mutations in the CHD7 gene. Few familial cases of this syndrome have been reported and these were characterized by a wide clinical variability. We here report on five CHD7 mutation positive families and comment on their clinical features. We observed somatic and germline mosaicism as well as parent‐to‐child transmission of non‐mosaic CHD7 mutations as causes of familial CHARGE syndrome. In one family with two affected sibs a somatic mutation was identified in lymphocytes of a clinically unaffected parent (2520G > A in exon 8). This is the second report of somatic CHD7 mosaicism in an unaffected parent. In two further families with affected siblings, we could not detect the mutation in parental lymphocytes suggesting germline mosaicism. The previously reported clinical variability was strikingly present in all five families. We find that alterations in CHD7 can result in a very mild phenotype, characterized by only a few minor symptoms of the CHARGE syndrome clinical spectrum. Such a mild phenotype was present in two families that shared the same 6322G > A missense mutation. These two families showed parent‐to‐child transmission. Phenotypically milder forms of CHARGE syndrome have a higher risk of transmission to multiple family members.

Detailed phenotype-genotype study in five patients with chromosome 6q16 deletion : narrowing the critical region for Prader-Willi-like phenotype

Most patients with an interstitial deletion of 6q16 have Prader–Willi-like phenotype, featuring obesity, hypotonia, short hands and feet, and developmental delay. In all reported studies, the chromosome rearrangement was detected by karyotype analysis, which provides an overview of the entire genome but has limited resolution. Here we describe a detailed clinical presentation of five patients, two of whom were previously reported, with overlapping interstitial 6q16 deletions and Prader–Willi-like phenotype. Our patients share the following main features with previously reported cases: global developmental delay, hypotonia, obesity, hyperphagia, and eye/vision anomalies. All rearrangement breakpoints have been accurately defined through array-CGH at about 100 Kb resolution. We were able to narrow the shortest region of deletion overlap for the presumed gene(s) involved in the Prader–Willi-like syndrome to 4.1 Mb located at 6q16.1q16.2. Our results support the evidence that haploinsufficiency of the SIM1 gene is responsible for obesity in these patients. A possible involvement of the GRIK2 gene in autistic-like behaviour, of POPDC3 in heart development, and of MCHR2 in the control of feeding behaviour and energy metabolism is also hypothesized.

Localizing a putative mutation as the major contributor to the development of sporadic Hirschsprung disease to the RET genomic sequence between the promoter region and exon 2

Hirschsprung disease (HSCR), a congenital disorder characterized by intestinal obstruction due to absence of enteric ganglia along variable lengths of the intestinal tract, occurs both in familial and sporadic cases. RET mutations have been found in approximately 50% of the families, but explains only a minority of sporadic cases. This study aims at investigating a possible role of RET in sporadic HSCR patients. Haplotypes of 13 DNA markers, within and flanking RET, have been determined for 117 sporadic HSCR patients and their parents. Strong association was observed for six markers in the 5′ region of RET. The largest distortions in allele transmission were found at the same markers. One single haplotype composed of these six markers was present in 55.6% of patients versus 16.2% of controls. Odds ratios (ORs) revealed a highly increased risk of homozygotes for this haplotype to develop HSCR (OR>20). These results allowed us to conclude that RET plays a crucial role in HSCR even when no RET mutations are found. An unknown functional disease variant(s) with a dosage-dependent effect in HSCR is likely located between the promoter region and exon 2 of RET.

FISH and array-CGH analysis of a complex chromosome 3 aberration suggests that loss of CNTN4 and CRBN contributes to mental retardation in 3pter deletions.

Imbalances of 3p telomeric sequences cause 3p− and trisomy 3p syndrome, respectively, showing distinct, but also shared clinical features. No causative genes have been identified in trisomy 3p patients, but for the 3p− syndrome, there is growing evidence that monosomy for one or more of four genes at 3pter, CHL1, CNTN4, CRBN, and MEGAP/srGAP3, may play a causative role. We describe here an analysis of a complex chromosome 3p aberration in a severely mentally retarded patient that revealed two adjacent segments with different copy number gains and a distal deletion. The deletion in this patient included the loci for CHL1, CNTN4, and CRBN, and narrowed the critical segment associated with the 3p− syndrome to 1.5 Mb, including the loci for CNTN4 and CRBN. We speculate that the deletion contributes more to this patients phenotype than the gains that were observed. We suggest that 3p− syndrome associated features are primarily caused by loss of CNTN4 and CRBN, with loss of CHL1 probably having an additional detrimental effect on the cognitive functioning of the present patient.

Cost of care of patients with cystic fibrosis in The Netherlands in 1990-1

BACKGROUND: Research on the cost of care of patients with cystic fibrosis is scarce. The aim of this study was to estimate the costs using age-specific medical consumption from real patient data. METHODS: The age-specific medical consumption of patients with cystic fibrosis in The Netherlands in 1991 was estimated from a survey of medical records and a patient questionnaire. A distinction was made between costs of hospital care, hospital and non-hospital medication, and home care. Costs per year were obtained by multiplying the yearly amount of care and the costs per unit. RESULTS: On average the annual cost of a patient with cystic fibrosis in 1991 was 10,908 pounds (hospital care 42%, medication 37%, home care 20%). The cost of care of cystic fibrosis in The Netherlands, with approximately 1000 patients, is estimated at 10.9 million pounds per year, which is 0.07% of the total health care budget. The cost of care of a patient up to the age of 35 is estimated at 614,587 pounds. When year-to-year survival is taken into account and future costs are discounted to the year of birth with a yearly discount rate of 5%, the cost of care of a patient with cystic fibrosis is estimated at 164,365 pounds for 1991. This estimate will be used in a prospective evaluation of screening for cystic fibrosis carriers. CONCLUSIONS: The cost of care of patients with cystic fibrosis estimated by age-specific medical consumption of real patients is higher than that estimated by non-age-specific medical consumption and/or expert opinions.

Mutation screening of the Ectodysplasin-A receptor gene EDAR in hypohidrotic ectodermal dysplasia

Hypohidrotic ectodermal dysplasia (HED) can be caused by mutations in the X-linked ectodysplasin A (ED1) gene or the autosomal ectodysplasin A-receptor (EDAR) and EDAR-associated death domain (EDARADD) genes. X-linked and autosomal forms are sometimes clinically indistinguishable. For genetic counseling in families, it is therefore important to know the gene involved. In 24 of 42 unrelated patients with features of HED, we found a mutation in ED1. ED1-negative patients were screened for mutations in EDAR and EDARADD. We found mutations in EDAR in 5 of these 18 patients. One mutation, p.Glu354X, is novel. In EDARADD, a novel variant p.Ser93Phe, probably a neutral polymorphism, was also found. Clinically, there was a difference between autosomal dominant and autosomal recessive HED patients. The phenotype in patients with mutations in both EDAR alleles was comparable to males with X-linked HED. Patients with autosomal dominant HED had features comparable to those of female carriers of X-linked HED. The teeth of these patients were quite severely affected. Hypohidrosis and sparse hair were also evident, but less severe. This study confirms Chassaing et als earlier finding that mutations in EDAR account for approximately 25% of non-ED1-related HED. Mutations leading to a premature stop codon have a recessive effect except when the stop codon is in the last exon. Heterozygous missense mutations in the functional domains of the gene may have a dominant-negative effect with much variation in expression. Patients with homozygous or compound heterozygous mutations in the EDAR gene have a more severe phenotype than those with a heterozygous missense, nonsense or frame-shift mutation.

The clinical spectrum of complete FBN1 allele deletions

The most common mutations found in FBN1 are missense mutations (56%), mainly substituting or creating a cysteine in a cbEGF domain. Other mutations are frameshift, splice and nonsense mutations. There are only a few reports of patients with marfanoid features and a molecularly proven complete deletion of a FBN1 allele. We describe the clinical features of 10 patients with a complete FBN1 gene deletion. Seven patients fulfilled the Ghent criteria for Marfan syndrome (MFS). The other three patients were examined at a young age and did not (yet) present the full clinical picture of MFS yet. Ectopia lentis was present in at least two patients. Aortic root dilatation was present in 6 of the 10 patients. In three patients, the aortic root diameter was on the 95th percentile and in one patient, the diameter of the aortic root was normal, the cross-section, however, had a cloverleaf appearance. Two patients underwent aortic root surgery at a relatively young age (27 and 34 years). Mitral valve prolapse was present in 4 of the 10 patients, and billowing of the mitral valve in 1. All patients had facial and skeletal features of MFS. Two patients with a large deletion extending beyond the FBN1 gene had an extended phenotype. We conclude that complete loss of one FBN1 allele does not predict a mild phenotype, and these findings support the hypothesis that true haploinsufficiency can lead to the classical phenotype of Marfan syndrome.

Split hand/foot malformation due to chromosome 7q aberrations(SHFM1): additional support for functional haploinsufficiency as the causative mechanism.

We report on three patients with split hand/foot malformation type 1 (SHFM1). We detected a deletion in two patients and an inversion in the third, all involving chromosome 7q21q22. We performed conventional chromosomal analysis, array comparative genomic hybridization and fluorescence in situ hybridization. Both deletions included the known genes associated with SHFM1 (DLX5, DLX6 and DSS1), whereas in the third patient one of the inversion break points was located just centromeric to these genes. These observations confirm that haploinsufficiency due to either a simultaneous deletion of these genes or combined downregulation of gene expression due to a disruption in the region between these genes and a control element could be the cause of the syndrome. We review previously reported studies that support this hypothetical mechanism.

Balanced into array: genome-wide array analysis in 54 patients with an apparently balanced de novo chromosome rearrangement and a meta-analysis

High-resolution genome-wide array analysis enables detailed screening for cryptic and submicroscopic imbalances of microscopically balanced de novo rearrangements in patients with developmental delay and/or congenital abnormalities. In this report, we added the results of genome-wide array analysis in 54 patients to data on 117 patients from seven other studies. A chromosome imbalance was detected in 37% of all patients with two-breakpoint rearrangements. In 49% of these patients, the imbalances were located in one or both breakpoint regions. Imbalances were more frequently (90%) found in complex rearrangements, with the majority (81%) having deletions in the breakpoint regions. The size of our own cohort enabled us to relate the presence of an imbalance to the clinical features of the patients by using a scoring system, the De Vries criteria, that indicates the complexity of the phenotype. The median De Vries score was significantly higher (P=0.002) in those patients with an imbalance (5, range 1–9) than in patients with a normal array result (3, range 0–7). This study provides accurate percentages of cryptic imbalances that can be detected by genome-wide array analysis in simple and complex de novo microscopically balanced chromosome rearrangements and confirms that these imbalances are more likely to occur in patients with a complex phenotype.