Raoul C. M. Hennekam

LDL Receptor-Related Protein 5 (LRP5) Affects Bone Accrual and Eye Development

In humans, low peak bone mass is a significant risk factor for osteoporosis. We report that LRP5, encoding the low-density lipoprotein receptor-related protein 5, affects bone mass accrual during growth. Mutations in LRP5 cause the autosomal recessive disorder osteoporosis-pseudoglioma syndrome (OPPG). We find that OPPG carriers have reduced bone mass when compared to age- and gender-matched controls. We demonstrate LRP5 expression by osteoblasts in situ and show that LRP5 can transduce Wnt signaling in vitro via the canonical pathway. We further show that a mutant-secreted form of LRP5 can reduce bone thickness in mouse calvarial explant cultures. These data indicate that Wnt-mediated signaling via LRP5 affects bone accrual during growth and is important for the establishment of peak bone mass.

Revised diagnostic criteria for the Marfan syndrome

In 1986, the diagnosis of the Marfan syndrome was codified on the basis of clinical criteria in the Berlin nosology [Beighton et al., 1988]. Over time, weaknesses have emerged in these criteria, a problem accentuated by the advent of molecular testing. In this paper, we propose a revision of diagnostic criteria for Marfan syndrome and related conditions. Most notable are: more stringent requirements for diagnosis of the Marfan syndrome in relatives of an unequivocally affected individual; skeletal involvement as a major criterion if at least 4 of 8 typical skeletal manifestations are present; potential contribution of molecular analysis to the diagnosis of Marfan syndrome; and delineation of initial criteria for diagnosis of other heritable conditions with partially overlapping phenotypes.

Heterozygous Germline Mutations in the p53 Homolog p63 Are the Cause of EEC Syndrome

EEC syndrome is an autosomal dominant disorder characterized by ectrodactyly, ectodermal dysplasia, and facial clefts. We have mapped the genetic defect in several EEC syndrome families to a region of chromosome 3q27 previously implicated in the EEC-like disorder, limb mammary syndrome (LMS). Analysis of the p63 gene, a homolog of p53 located in the critical LMS/EEC interval, revealed heterozygous mutations in nine unrelated EEC families. Eight mutations result in amino acid substitutions that are predicted to abolish the DNA binding capacity of p63. The ninth is a frameshift mutation that affects the p63alpha, but not p63beta and p63gamma isotypes. Transactivation studies with these mutant p63 isotypes provide a molecular explanation for the dominant character of p63 mutations in EEC syndrome.

Recurrent rearrangements of chromosome 1q21.1 and variable pediatric phenotypes

BACKGROUND Duplications and deletions in the human genome can cause disease or predispose persons to disease. Advances in technologies to detect these changes allow for the routine identification of submicroscopic imbalances in large numbers of patients. METHODS We tested for the presence of microdeletions and microduplications at a specific region of chromosome 1q21.1 in two groups of patients with unexplained mental retardation, autism, or congenital anomalies and in unaffected persons. RESULTS We identified 25 persons with a recurrent 1.35-Mb deletion within 1q21.1 from screening 5218 patients. The microdeletions had arisen de novo in eight patients, were inherited from a mildly affected parent in three patients, were inherited from an apparently unaffected parent in six patients, and were of unknown inheritance in eight patients. The deletion was absent in a series of 4737 control persons (P=1.1x10(-7)). We found considerable variability in the level of phenotypic expression of the microdeletion; phenotypes included mild-to-moderate mental retardation, microcephaly, cardiac abnormalities, and cataracts. The reciprocal duplication was enriched in nine children with mental retardation or autism spectrum disorder and other variable features (P=0.02). We identified three deletions and three duplications of the 1q21.1 region in an independent sample of 788 patients with mental retardation and congenital anomalies. CONCLUSIONS We have identified recurrent molecular lesions that elude syndromic classification and whose disease manifestations must be considered in a broader context of development as opposed to being assigned to a specific disease. Clinical diagnosis in patients with these lesions may be most readily achieved on the basis of genotype rather than phenotype.

Discovery of previously unidentified genomic disorders from the duplication architecture of the human genome

Genomic disorders are characterized by the presence of flanking segmental duplications that predispose these regions to recurrent rearrangement. Based on the duplication architecture of the genome, we investigated 130 regions that we hypothesized as candidates for previously undescribed genomic disorders. We tested 290 individuals with mental retardation by BAC array comparative genomic hybridization and identified 16 pathogenic rearrangements, including de novo microdeletions of 17q21.31 found in four individuals. Using oligonucleotide arrays, we refined the breakpoints of this microdeletion, defining a 478-kb critical region containing six genes that were deleted in all four individuals. We mapped the breakpoints of this deletion and of four other pathogenic rearrangements in 1q21.1, 15q13, 15q24 and 17q12 to flanking segmental duplications, suggesting that these are also sites of recurrent rearrangement. In common with the 17q21.31 deletion, these breakpoint regions are sites of copy number polymorphism in controls, indicating that these may be inherently unstable genomic regions.

Germline KRAS and BRAF mutations in cardio-facio-cutaneous syndrome

Cardio-facio-cutaneous (CFC) syndrome is characterized by a distinctive facial appearance, heart defects and mental retardation. It phenotypically overlaps with Noonan and Costello syndrome, which are caused by mutations in PTPN11 and HRAS, respectively. In 43 individuals with CFC, we identified two heterozygous KRAS mutations in three individuals and eight BRAF mutations in 16 individuals, suggesting that dysregulation of the RAS-RAF-ERK pathway is a common molecular basis for the three related disorders.

Holoprosencephaly due to mutations in ZIC2 , a homologue of Drosophila odd-paired

Holoprosencephaly (HPE) is the most common structural anomaly of the human brain and is one of the anomalies seen in patients with deletions and duplications of chromosome 13. On the basis of molecular analysis of a series of patients with hemizygous deletions of the long arm of chromosome 13, we have defined a discrete region in band 13q32 where deletion leads to major developmental anomalies (the 13q32 deletion syndrome). This approximately 1-Mb region 1 lies between markers D13S136 and D13S147. Patients in which this region is deleted usually have major congenital malformations, including brain anomalies such as HPE or exencephaly, and digital anomalies such as absent thumbs2. We now report that human ZIC2 maps to this critical deletion region and that heterozygous mutations in ZIC2 are associated with HPE. Haploinsufficiency for ZIC2 is likely to cause the brain malformations seen in 13q deletion patients.

Hutchinson-Gilford progeria syndrome: review of the phenotype.

Hutchinson–Gilford progeria syndrome (HGPS) is a rare but well known entity characterized by extreme short stature, low body weight, early loss of hair, lipodystrophy, scleroderma, decreased joint mobility, osteolysis, and facial features that resemble aged persons. Cardiovascular compromise leads to early demise. Cognitive development is normal. Data on 10 of our own cases and 132 cases from literature are presented. The incidence in the last century in the Netherlands was 1:4,000,000. Sex ratio was 1.2:1. Main first symptoms were failure to thrive (55%), hair loss (40%), skin problems (28%), and lipodystrophy (20%). Mean age at diagnosis was 2.9 years. Growth in weight was more disturbed than growth in height, and growth delay started already prenatally. Mean height > 13 years was 109.0 cm, mean weight was 14.5 kg. Osteolysis was wide‐spread but not expressed, except in the viscerocranium, and remained limited to membranous formed bone. Lipodystrophy is generalized, only intra‐abdominal fat depositions remain present. Cardiovascular problems are extremely variable, both in age of onset and nature. Stroke and coronary dysfunctioning are most frequent. Pathologic findings in coronaries and aorta resemble sometimes the findings in elderly persons, but can also be much more limited. Loss of smooth muscle cells seems the most important finding. Mean age of demise was 12.6 years. Patients can be subdivided in patients with classical HGPS, which follows an autosomal dominant pattern of inheritance, (almost) all cases representing spontaneous mutations, and in non‐classical progeria, in whom growth can be less retarded, scalp hair remains present for a longer time, lipodystrophy is more slowly progressive, osteolysis is more expressed except in the face, and survival well into adulthood is not uncommon. Pattern of inheritance of non‐classical progeria is most probably autosomal recessive. The cause of HGPS is an abnormally formed Lamin A, either directly by a mutated LMNA gene, or through abnormal posttranslational processing (ZMPSTE24 gene mutations). Of 34 LMNA mutations found in progeria patients, there were 26 classical p.G608G mutations (76%). Pathogenesis is most likely to follow several different pathways. Potential therapeutic strategies are developed along these lines and include RNA interference techniques and inhibition of the dominant‐negative influence of abnormally formed Lamin A on polymerization with normally formed Lamin A.

Genetic heterogeneity in Rubinstein-Taybi syndrome: mutations in both the CBP and EP300 genes cause disease

CREB-binding protein and p300 function as transcriptional coactivators in the regulation of gene expression through various signal-transduction pathways. Both are potent histone acetyl transferases. A certain level of CREB-binding protein is essential for normal development, since inactivation of one allele causes Rubinstein-Taybi syndrome (RSTS). There is a direct link between loss of acetyl transferase activity and RSTS, which indicates that the disorder is caused by aberrant chromatin regulation. We screened the entire CREB-binding protein gene (CBP) for mutations in patients with RSTS by using methods that find point mutations and larger rearrangements. In 92 patients, we were able to identify a total of 36 mutations in CBP. By using multiple ligation-dependent probe amplification, we found not only several deletions but also the first reported intragenic duplication in a patient with RSTS. We extended the search for mutations to the EP300 gene and showed that mutations in EP300 also cause this disorder. These are the first mutations identified in EP300 for a congenital disorder.

Mutations in the Pericentrin (PCNT) Gene Cause Primordial Dwarfism

Fundamental processes influencing human growth can be revealed by studying extreme short stature. Using genetic linkage analysis, we find that biallelic loss-of-function mutations in the centrosomal pericentrin (PCNT) gene on chromosome 21q22.3 cause microcephalic osteodysplastic primordial dwarfism type II (MOPD II) in 25 patients. Adults with this rare inherited condition have an average height of 100 centimeters and a brain size comparable to that of a 3-month-old baby, but are of near-normal intelligence. Absence of PCNT results in disorganized mitotic spindles and missegregation of chromosomes. Mutations in related genes are known to cause primary microcephaly (MCPH1, CDK5RAP2, ASPM, and CENPJ).