Despite the increasing understanding of the mechanisms involved in their genesis, CCRs arise as unique, complex events for which the genetic and reproductive counseling of carriers remains a challenge.

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Obesity is a common but highly, clinically, and genetically heterogeneous disease. Deletion of the terminal region of the short arm of chromosome 2 is rare and has been reported in about 13 patients in the literature often associated with a Prader-Willi-like phenotype. We report on five unrelated patients with 2p25 deletion of paternal origin presenting with earlyonset obesity, hyperphagia, intellectual deficiency, and behavioural difficulties. Among these patients, three had de novo pure 2pter deletions, one presented with a paternal derivative der(2)t(2;15)(p25.3;q26) with deletion in the 2pter region and the last patient presented with an interstitial 2p25 deletion. The size of the deletions was characterized by SNP array or array-CGH and was confirmed by fluorescence in situ hybridization (FISH) studies. Four patients shared a 2p25.3 deletion with a minimal critical region estimated at 1.97 Mb and encompassing seven genes, namely SH3HYL1, ACP1, TMEMI8, SNTG2, TPO, PXDN, and MYT1L genes. The fifth patient had a smaller interstitial deletion encompassing the TPO, PXDN, and MYT1L genes. Paternal origin of the deletion was determined by genotyping using microsatellite markers. Analysis of the genes encompassed in the deleted region led us to speculate that the ACP1, TMEM18, and/or MYT1L genes might be involved in early-onset obesity. In addition, intellectual deficiency and behavioural troubles can be explained by the heterozygous loss of the SNTG2 and MYT1L genes. Finally, we discuss the parent-of-origin of the deletion.

Intellectual disability (ID) is frequent in the general population, with 1 in 50 individuals directly affected worldwide. The multiple etiologies include X-linked ID (XLID). Among syndromic XLID, few syndromes present severe ID associated with postnatal microcephaly and midline stereotypic hand movements. We report on three male patients with ID, midline stereotypic hand movements, hypotonia, hyperkinesia, strabismus, as well as seizures (2/3), and non-inherited and postnatal onset microcephaly (2/3). Using array CGH and exome sequencing we characterised two truncating mutations in IQSEC2, namely two de novo intragenic duplication mapped to the Xp11.22 region and a nonsense mutation in exon 7. We propose that truncating mutations in IQSEC2 are responsible for syndromic severe ID in male patients and should be screened in patients without mutations in MECP2, FOXG1, CDKL5 and MEF2C. Keywords: syndromic X-linked intellectual disability; microcephaly; IQSEC2-truncating mutations INTRODUCTIONIntellectual disability (ID) is defined by substantial limitations in cognitive functioning (intellectual quotient o70) coupled with a deficit in adaptive behaviour and onset before the age of 18 years. ID is frequent in the general population, with as many as 1 in every 50 individuals directly affected worldwide. 1,2 Among the genetic etiologies of ID, XLID is a frequent cause, estimated at 5-10% of all cases in males, with a major genetic heterogeneity. Indeed, more than 102 genes have been involved in syndromic form of XLID, making molecular diagnosis and thus genetic counselling difficult. 2-4 Among XLID, syndromic and nonsyndromic forms are delineated based on observed additional features that are associated with ID such as seizures, abnormal growth parameters, visceral or cerebral malformation, and so on. Recently, mutations in IQSEC2 (Sec7 domain of, and IQ-like domain) have been shown to cause nonsyndromic XLID with behavioural disturbance. 5-8 We report on three male patients with severe syndromic XLID and truncating mutations in IQSEC2. PATIENTS AND METHODS Patient 1This patient was referred to the Genetics Department for severe ID and postnatal microcephaly. He is the only child born to healthy unrelated parents native to the south of France. Pregnancy was uneventful. The boy was born at 37 ½ weeks of gestation full term by caesarean section due to an abnormal presentation. Birth measurements were in the normal range (occipital frontal circumference (OFC) 36 cm, þ 1 SD; birth weight 3430 g, mean; birth length 52.5 cm, þ 1 SD). Postnatal course was marked by psychomotor retardation with neonatal hypotonia, hyperkinesia, strabismus and non-inherited progressive postnatal microcephaly with OFC at À2 SD at 6 months of age. He sat at 12 months and did not vocalize at 15 months. At the time of the last evaluation, he was 4 years old. He presented with normal facial features ( Figure 1a). OFC was at 48 cm, À2.5 SD; weight at 2 kg, þ 2 SD and length at 106 cm, þ 1 SD. Language was not acquired and he could not walk alone. He h...

The possibility that a chromosomal rearrangement might disturb the meiotic behaviour of chromosomes not involved in the rearrangement and favour non-disjunction is a controversial issue in human cytogenetics. Using two-colour fluorescence in-situ hybridization and primed in-situ labelling techniques, we have investigated the segregation pattern of 10 chromosomes (chromosomes 1, 4, 9, 13, 15, 16, 20, 21, X and Y) in spermatozoa from nine carriers of balanced structural rearrangements and three normal men. The patients were divided into two groups according to their semen parameters. In rearrangement carriers and normal subjects, sex chromosomes and chromosome 21 displayed a higher rate of disomy than the other chromosomes. No evidence for the occurrence of interchromosomal effect was found in the spermatozoa of fertile rearrangement carriers, but significant variations were observed for all chromosomes tested in the group of infertile translocation carriers, suggesting a direct correlation between poor quality spermatozoa and increased aneuploidy rate in this group. In fertile carriers of chromosomal rearrangements, the occurrence of non-disjunction of chromosomes not involved in the rearrangement might therefore be considered as fortuitous, whereas in infertile carriers, the risk for interchromosomal effect appears to be real and should be taken into consideration in the genetic counselling of infertile couples with a male partner carrying a chromosomal rearrangement.