Giant diencephalic harmartoma and related anomalies: a newly recognized entity distinct from the Pallister-Hall syndrome.

An hypothalamic hamartoma is an abnormal mass of mature glio-neuronal tissue present in the hypothalamic area. It usually measures <2 cm of diameter. Most of the time, this hamartoma occurs in Pallister-Hall syndrome (PHS), due to heterozygous GLI3 mutations. We report on five fetuses with giant diencephalic hamartoma and other midline brain and facial malformations, without mutation in the GLI3 gene or genomic rearrangements in three of them. The fetuses showed facial asymmetry, unilateral ear and eye anomalies, and facial cleft. Extracephalic malformations consisted of vertebral anomalies and short nails, without polydactyly and cardiac malformation. The diencephalon was replaced by an encephaloid mass protruding into the facial cleft. Normal cerebral structures were not detectable. In one patient, holoprosencephaly of the syntelencephalic type was noted. Arhinencephaly was present in all patients. Histologically, the ill-defined, multilobulated lesion was made of neuroblastic and neurocytic cell foci, lying in a fibrillar network, elaborating sometimes perivascular pseudorosettes, with a maturation gradient in accordance with the fetal age. Owing to their location, the tumors could be described as diencephalic, rather than hypothalamic hamartomas. The striking asymmetry of the facial anomalies and the diencephalic malformations are not in the spectrum observed with PHS and related syndromes, suggesting a distinct entity involving abnormal morphogenetic developmental fields at around 5 weeks of gestation.

Simple detection of genomic microdeletions and microduplications using QMPSF in patients with idiopathic mental retardation.

In contrast to the numerous well-known microdeletion syndromes, only a few microduplications have been described, and this discrepancy may be due in part to methodological bias. In order to facilitate the detection of genomic microdeletions and microduplications, we developed a new assay based on QMPSF (Quantitative Multiplex PCR of Short fluorescent Fragments) able to explore simultaneously 12 candidate loci involved in mental retardation (MR) and known to be the target of genomic rearrangements. We first screened 153 patients with MR and facial dysmorphism associated with malformations, or growth anomalies, or familial history, with cytogenetically normal chromosomes, and the absence of FRAXA mutation and subtelomeric rearrangements. In this series, we found a 5q35 deletion removing the NSD1 gene in a patient with severe epilepsy, profound MR and, retrospectively, craniofacial features of Sotos syndrome. In a second series, we screened 140 patients with MR and behaviour disturbance who did not fulfil the de Vries criteria for subtelomeric rearrangements and who had a normal karyotype and no detectable FRAXA mutation. We detected a 22q11 deletion in a patient with moderate MR, obesity, and facial dysmorphism and a 4 Mb 17p11 duplication in a patient with moderate MR, behaviour disturbance, strabismus, and aspecific facial features. This new QMPSF assay can be gradually upgraded to include additional loci involved in newly recognised microduplication/microdeletion syndromes, and should facilitate wide screenings of patients with idiopathic MR and provide better estimates of the microduplication frequency in the MR population.

Molecular characterization of a 14q deletion in a boy with features of Holt-Oram syndrome.

Holt-Oram syndrome, the major "heart-hand" syndrome is defined by the association of radial defects or triphalangeal thumbs and septal heart defects. The transmission is autosomal dominant and the causative gene has been shown to be TBX5, located on 12q24.1, which encodes a transcription factor. Genetic heterogeneity has been suggested by several reports. We identified a 14(q23.3 approximately 24.2q31.1) deletion in a boy presenting severe bilateral asymmetrical radial aplasia, congenital heart defects, and developmental delay. This deletion, whose size could be estimated to be 9.6-13.7 Mb, was shown to be inherited via his mother's interchromosomal insertion. This is the second report of a chromosome 14 interstitial deletion associated with clinical features of Holt-Oram syndrome. These observations suggest the existence of a new "heart-hand" locus on chromosome 14q.

Complete germline deletion of the STK11 gene in a family with Peutz-Jeghers syndrome.

Peutz-Jeghers syndrome (PJS, MIM175200) is an autosomal-dominant inherited disorder characterised by multiple gastrointestinal hamartomatous polyps, melanin spots of the oral mucosa and digits, and an increased risk for various neoplasms. The PJS results from germline alterations of the STK11/LKB1 tumour suppressor gene, located on 19p13.3, and encoding a serine/threonine kinase. The detection of STK11 germline mutations, in only 50-70% of PJS families, has suggested a genetic heterogeneity of the disease. We report the case of a family with typical features of PJS, including gastrointestinal hamartomatous, breast cancers and melanin spots of the oral mucosa. Quantitative multiplex PCR of short fluorescent fragments (QMPSF) of the 19p13 region allowed us to identify an approximately 250 kb heterozygous deletion removing entirely the STK11 locus. This report, which constitutes the first description of a complete germline deletion of STK11, shows that the presence of such large genomic deletions should be considered in PJS families without detectable point mutations of STK11.

Mechanism of intrachromosomal triplications 15q11-q13: a new clinical report.

We describe here a patient with intrachromosomal triplication 15q11-q13, a rare chromosomal event associated with severe mental retardation and intractable epilepsy. Cytogenetic studies including FISH on interphasic nuclei showed that the middle segment of the triplication was inverted in orientation. Molecular analyses demonstrated that the rearrangement was of maternal origin. Based on these cytogenetic and molecular data and those of the nine cases reported in the literature, we discuss the mechanistic origins of these triplications. We present several arguments for the mechanism involving two U-type exchanges occurring simultaneously at the pachytene stage of meiosis.