Frank Kooy

Abnormal dendritic spine characteristics in the temporal and visual cortices of patients with fragile‐X syndrome: A quantitative examination

Fragile-X syndrome is a common form of mental retardation resulting from the inability to produce the fragile-X mental retardation protein. Qualitative examination of human brain autopsy material has shown that fragile-X patients exhibit abnormal dendritic spine lengths and shapes on parieto-occipital neocortical pyramidal cells. Similar quantitative results have been obtained in fragile-X knockout mice, that have been engineered to lack the fragile-X mental retardation protein. Dendritic spines on layer V pyramidal cells of human temporal and visual cortices stained using the Golgi-Kopsch method were investigated. Quantitative analysis of dendritic spine length, morphology, and number was carried out on patients with fragile-X syndrome and normal age-matched controls. Fragile-X patients exhibited significantly more long dendritic spines and fewer short dendritic spines than did control subjects in both temporal and visual cortical areas. Similarly, fragile-X patients exhibited significantly more dendritic spines with an immature morphology and fewer with a more mature type morphology in both cortical areas. In addition, fragile-X patients had a higher density of dendritic spines than did controls on distal segments of apical and basilar dendrites in both cortical areas. Long dendritic spines with immature morphologies and elevated spine numbers are characteristic of early development or a lack of sensory experience. The fact that these characteristics are found in fragile-X patients throughout multiple cortical areas may suggest a global failure of normal dendritic spine maturation and or pruning during development that persists throughout adulthood.

Further delineation of the 15q13 microdeletion and duplication syndromes: a clinical spectrum varying from non-pathogenic to a severe outcome

Background: Recurrent 15q13.3 microdeletions were recently identified with identical proximal (BP4) and distal (BP5) breakpoints and associated with mild to moderate mental retardation and epilepsy. Methods: To assess further the clinical implications of this novel 15q13.3 microdeletion syndrome, 18 new probands with a deletion were molecularly and clinically characterised. In addition, we evaluated the characteristics of a family with a more proximal deletion between BP3 and BP4. Finally, four patients with a duplication in the BP3–BP4–BP5 region were included in this study to ascertain the clinical significance of duplications in this region. Results: The 15q13.3 microdeletion in our series was associated with a highly variable intra- and inter-familial phenotype. At least 11 of the 18 deletions identified were inherited. Moreover, 7 of 10 siblings from four different families also had this deletion: one had a mild developmental delay, four had only learning problems during childhood, but functioned well in daily life as adults, whereas the other two had no learning problems at all. In contrast to previous findings, seizures were not a common feature in our series (only 2 of 17 living probands). Three patients with deletions had cardiac defects and deletion of the KLF13 gene, located in the critical region, may contribute to these abnormalities. The limited data from the single family with the more proximal BP3–BP4 deletion suggest this deletion may have little clinical significance. Patients with duplications of the BP3–BP4–BP5 region did not share a recognisable phenotype, but psychiatric disease was noted in 2 of 4 patients. Conclusions: Overall, our findings broaden the phenotypic spectrum associated with 15q13.3 deletions and suggest that, in some individuals, deletion of 15q13.3 is not sufficient to cause disease. The existence of microdeletion syndromes, associated with an unpredictable and variable phenotypic outcome, will pose the clinician with diagnostic difficulties and challenge the commonly used paradigm in the diagnostic setting that aberrations inherited from a phenotypically normal parent are usually without clinical consequences.

Germline mutation of microRNA-125a is associated with breast cancer

MicroRNAs (miRNAs) are small non-coding RNAs that inhibit expression of specific target genes at the posttranscriptional level. MiRNAs are often found to be misregulated in human cancer, and they can act as either potent oncogenes or tumour suppressor genes. Here we show that a germline mutation in mature miR-125a is highly associated with breast cancer tumorigenesis, suggesting that miR-125a is likely to function as a tumour suppressor gene in human cancer.

Clinical and molecular characteristics of 1qter microdeletion syndrome: delineating a critical region for corpus callosum agenesis/hypogenesis

Background: Patients with a microscopically visible deletion of the distal part of the long arm of chromosome 1 have a recognisable phenotype, including mental retardation, microcephaly, growth retardation, a distinct facial appearance and various midline defects including corpus callosum abnormalities, cardiac, gastro-oesophageal and urogenital defects, as well as various central nervous system anomalies. Patients with a submicroscopic, subtelomeric 1qter deletion have a similar phenotype, suggesting that the main phenotype of these patients is caused by haploinsufficiency of genes in this region. Objective: To describe the clinical presentation of 13 new patients with a submicroscopic deletion of 1q43q44, of which nine were interstitial, and to report on the molecular characterisation of the deletion size. Results and conclusions: The clinical presentation of these patients has clear similarities with previously reported cases with a terminal 1q deletion. Corpus callosum abnormalities were present in 10 of our patients. The AKT3 gene has been reported as an important candidate gene causing this abnormality. However, through detailed molecular analysis of the deletion sizes in our patient cohort, we were able to delineate the critical region for corpus callosum abnormalities to a 360 kb genomic segment which contains four possible candidate genes, but excluding the AKT3 gene.

Mutation of the iron-sulfur cluster assembly gene IBA57 causes severe myopathy and encephalopathy

Two siblings from consanguineous parents died perinatally with a condition characterized by generalized hypotonia, respiratory insufficiency, arthrogryposis, microcephaly, congenital brain malformations and hyperglycinemia. Catalytic activities of the mitochondrial respiratory complexes I and II were deficient in skeletal muscle, a finding suggestive of an inborn error in mitochondrial biogenesis. Homozygosity mapping identified IBA57 located in the largest homozygous region on chromosome 1 as a culprit candidate gene. IBA57 is known to be involved in the biosynthesis of mitochondrial [4Fe-4S] proteins. Sequence analysis of IBA57 revealed the homozygous mutation c.941A > C, p.Gln314Pro. Severely decreased amounts of IBA57 protein were observed in skeletal muscle and cultured skin fibroblasts from the affected subjects. HeLa cells depleted of IBA57 showed biochemical defects resembling the ones found in patient-derived cells, including a decrease in various mitochondrial [4Fe-4S] proteins and in proteins covalently linked to lipoic acid (LA), a cofactor produced by the [4Fe-4S] protein LA synthase. The defects could be complemented by wild-type IBA57 and partially by mutant IBA57. As a result of the mutation, IBA57 protein was excessively degraded, an effect ameliorated by protease inhibitors. Hence, we propose that the mutation leads to partial functional impairment of IBA57, yet the major pathogenic impact is due to its proteolytic degradation below physiologically critical levels. In conclusion, the ensuing lethal complex biochemical phenotype of a novel metabolic syndrome results from multiple Fe/S protein defects caused by a deficiency in the Fe/S cluster assembly protein IBA57.

Implementation of genomic arrays in prenatal diagnosis: The Belgian approach to meet the challenges

After their successful introduction in postnatal testing, genome-wide arrays are now rapidly replacing conventional karyotyping in prenatal diagnostics. While previous studies have demonstrated the advantages of this method, we are confronted with difficulties regarding the technology and the ethical dilemmas inherent to genomic arrays. These include indication for testing, array design, interpretation of variants and how to deal with variants of unknown significance and incidental findings. The experiences with these issues reported in the literature are most often from single centres. Here, we report on a national consensus approach how microarray is implemented in all genetic centres in Belgium. These recommendations are subjected to constant re-evaluation based on our growing experience and can serve as a useful tool for those involved in prenatal diagnosis.

Dandy-Walker complex in a boy with a 5 Mb deletion of region 1q44 due to a paternal t(1;20)(q44;q13.33).

A 10‐year‐old boy with vermis hypoplasia, dilatation of the fourth ventricle, enlarged cisterna magna and aplasia of the corpus callosum, consistent with the Dandy‐Walker complex (DWC), and slight facial dysmorphisms, severe motor and mental retardation is presented. By combining data obtained by karyotyping, array‐CGH, FISH, and multiplex ligation‐mediated probe amplification (MLPA) we identified a 5 Mb deletion of the 1q44 → qter region resulting from a paternal t(1;20)(q44;q13.33). This smallest 1q44 deletion reported so far, enabled us to significantly narrow down the number of candidate genes for the DWC in this region. Since the ZNF124 transcription factor is strongly expressed in the fetal brain it may represent a candidate gene for the DWC at 1q44.

A New Neurological Syndrome with Mental Retardation, Choreoathetosis, and Abnormal Behavior Maps to Chromosome Xp11

Choreoathetosis is a major clinical feature in only a small number of hereditary neurological disorders. We define a new X-linked syndrome with a unique clinical picture characterized by mild mental retardation, choreoathetosis, and abnormal behavior. We mapped the disease in a four-generation pedigree to chromosome Xp11 by linkage analysis and defined a candidate region containing a number of genes possibly involved in neuronal signaling, including a potassium channel gene and a neuronal G protein-coupled receptor.

Mice lacking Dfna5 show a diverging number of cochlear fourth row outer hair cells

A complex mutation in DFNA5, resulting in exon 8 skipping, causes autosomal dominant hearing impairment, which starts in the high frequencies between 5 and 15 years of age and progressively affects all frequencies. To study its function in vivo, Dfna5 knockout mice were generated through the deletion of exon 8, simultaneously mimicking the human mutation. To test the hearing impairment, frequency-specific Auditory Brainstem Response (ABR) measurements were performed at different ages in two genetic backgrounds (C57Bl/6J and CBA/Ca), but no differences between Dfna5-/- and Dfna5+/+ mice could be demonstrated. Morphological studies demonstrated significant differences in the number of fourth row outer hair cells between Dfna5-/- mice and their wild-type littermates. These results were obtained in both genetic backgrounds, albeit with opposite effects. In contrast to the results obtained in Dfna5-/- zebrafish, we did not observe different UDP-glucose dehydrogenase and hyaluronic acid levels in Dfna5-/- mice when compared to Dfna5+/+ mice.

A novel 2 bp deletion in the TM4SF2 gene is associated with MRX58

X linked mental retardation (XLMR) represents around 5% of all MR, with a prevalence of 1 in 600 males.1,2 Fifteen to twenty percent of the total XLMR is the result of the fragile X syndrome.3 Non-fragile X mental retardation was subdivided into syndromal and non-syndromal conditions by Neri et al 4 in 1991. The syndromal XLMR entities (MRXS) are those in which there is a specific pattern of physical, neurological, or metabolic abnormalities associated with the presence of mental retardation.5 Non-syndromic XLMR (MRX) are conditions in which a gene mutation causes mental retardation in the absence of other distinctive dysmorphic, metabolic, or neurological features.6 At present, XLMR conditions consist of 136 MRXS7 and 75 MRX8 entities. To date, 35 genes have been cloned. However, so far only nine non-syndromic XLMR genes have been identified: TM4SF2 , FMR2 , OPHN1 (MRX60), GDI1 (MRX41, MRX48), PAK3 (MRX30, MRX47), RSK2 (MRX19), IL1RAPL (MRX34), ARHGEF6 (MRX46), and MECP2 (MRX16).9–18 TM4SF2 , a member of the transmembrane 4 superfamily, maps to Xp11.4 and is one of the genes associated with non-syndromic XLMR.9 Mutations in TM4SF2 have been previously described in two families (L28 and T15) with non-syndromic XLMR. As a part of our XLMR candidate gene testing, we have screened probands from 14 XLMR families (10 linked to Xp11 and four small families with no linkage data) for mutations in the TM4SF2 gene. Here we report a novel 2 bp deletion (564delGT), which segregates with mental retardation in the MRX58 family. The deletion causes a frameshift and a subsequent stop codon six amino acids downstream (stop codon 192). This finding supports the hypothesis that different XLMR conditions, especially non-syndromic XLMR, result from mutations in the same gene. ### Patients Probands from 14 XLMR families (three MRXS and …