S. Romana

Deletion of the SIM1 gene (6q16.2) in a patient with a Prader-Willi-like phenotype

Apart from Prader-Willi syndrome, which is a well delineated imprinting disorder of the 15q11-q12 region, other chromosome anomalies have been described in a small number of patients with features reminiscent of Prader-Willi syndrome, including hypotonia, progressive obesity, small extremities, and delayed developmental milestones. Among these chromosome anomalies are some cases of interstitial deletion of chromosome 6q1–5 and haploinsufficiency of the SIM1 gene (6q16.2) has been proposed as a candidate gene for obesity.6 Here, we report a fifth case of Prader-Willi-like phenotype associated with an interstitial chromosome 6q deletion (6q16.1-q21) detected only by high resolution banding techniques. This suggests that a subgroup of patients with features reminiscent of Prader-Willi syndrome and an interstitial deletion of chromosome 6q16.2 could be delineated. The proband was the only child of a 27 year old mother and a 32 year old father. Intrauterine growth retardation, oligohydramnios, and a left club foot were noted during the third trimester of pregnancy. He was born at term after a normal delivery. His growth parameters were weight 2350 g (−2.5 SD), length 47 cm (−1.5 SD), and OFC 33 cm (−1.5 SD). He was described as floppy and had feeding difficulties in early infancy. He sat at the age of 2 years, walked at 3½12 years, and had no speech when we first saw him aged 5 years. Excessive weight gain began at 3 years, with a big appetite and food seeking behaviour. There were no sleep disturbances. His behaviour was hyperactive, with a short attention span and …

Automated fluorescent genotyping detects 10% of cryptic subtelomeric rearrangements in idiopathic syndromic mental retardation

Recent studies have shown that cryptic unbalanced subtelomeric rearrangements contribute to a significant proportion of idiopathic syndromic mental retardation cases. Using a fluorescent genotyping based strategy, we found a 10% rate of cryptic subtelomeric rearrangements in a large series of 150 probands with severe idiopathic syndromic mental retardation and normal RHG-GTG banded karyotype. Fourteen children were found to carry deletions or duplications of one or more chromosome telomeres and two children had uniparental disomy. This study clearly shows that fluorescent genotyping is a sensitive and cost effective method that not only detects cryptic subtelomeric rearrangements but also provides a unique opportunity to detect uniparental disomies. We suggest giving consideration to systematic examination of subtelomeric regions in the diagnostic work up of patients with unexplained syndromic mental retardation.

PMX2B, a new candidate gene for hirschsprung's disease

Hirschsprungs (HSCR) disease is a congenital intestinal malformation of the enteric nervous system. It is a multigenic malformation and until now, eight genes have been involved in the etiology of this disease: genes encoding proteins of the RET signaling pathway (RET, GDNF and NTN), genes participating in the endothelin (EDN) type B receptor pathway (EDNRB, EDN3 and ECE‐1), the SOX10 gene and the SIP1 gene that is mutated in syndromic forms of HSCR. Mutations of these genes are found in not more than 50–60% of affected individuals. Here, we report on the results of a molecular cytogenetic study performed in a girl who presented with a syndromic short segment HSCR associated with a de novo t(4;8)(p13;p22) translocation. A comparative genomic hybridization (CGH) study found a 4p12p13 deletion. A molecular characterization of this rearrangement showed that the 4p13 deletion was 5 Mb in length and included the paired mesoderm homeobox gene (PMX2B) (MIM 603851), a gene expressed in the human embryonic gut and essential for the development of autonomic neural crest derivatives. The present observation suggests that PMX2B haploinsuffciency might predispose to HSCR.

Mild phenotype in a 15-year-old boy with Pallister–Killian syndrome

Pallister–Killian syndrome is a rare disorder characterized by multiple congenital anomalies, coarse face, pigmentary skin changes, seizures, severe mental retardation, and the presence of an extra metacentric chromosome i(12p) confined to skin fibroblasts only. Here, we report on an unusual case of i(12p) in a 15‐year‐old boy presenting with mild mental retardation, minor facial features (long face, prognathism, short neck), normal weight, length, and OFC parameters as well as hyperpigmented streaks. The boy attended normal school until the age of 14 years. Because of hyperpigmented stripes, chromosome analysis was performed on skin fibroblasts. This study showed that 37% of the cells had an additional isochromosome for the short arm of chromosome 12. This observation illustrates the phenotypic variability of i(12p) and emphasizes the importance of skin fibroblasts chromosome analysis in patients with pigmentary skin changes.

A CGH study of 27 patients with CHARGE association

CHARGE association is a non‐random occurrence of congenital malformations including coloboma, heart disease, choanal atresia, retarded growth and/or retarded development, genital hypoplasia, ear anomalies and/or deafness. The cause of this association remains unknown. Various genetic mechanisms have been proposed, including a contiguous gene syndrome but, so far, no recurrent locus has been identified. To address this question, we decided to perform a comparative genomic hybridization (CGH) study on a cohort of 27 patients with CHARGE association and a normal standard karyotype. We found two chromosomal anomalies: a der(9)t(9;13) derived from a paternal translocation and a der(6)t(4;6) of unknown origin. This suggests that chromosome imbalances may well mimic CHARGE association. Therefore patients with CHARGE association must be carefully tested with classical and molecular cytogenetic techniques to detect a potential chromosome imbalance. It is expected that more stringent diagnostic criteria of CHARGE association could define a more homogeneous group of patients where a single genetic cause might be identified.

Monozygotic twins discordant for submicroscopic chromosomal anomalies in 2p25.3 region detected by array CGH

Although discordant phenotypes in monozygotic twins with developmental disorder are not an exception, underlying genetic discordance is rarely reported. Here, we report on the clinical and cytogenetic details of 4‐year‐old female monozygotic twins with discordant phenotypes. Twin 1 exhibited global developmental delay, overweight and hyperactivity. Twin 2 had an autistic spectrum disorder. Molecular karyotyping in twin 1 identified a 2p25.3 deletion, further confirmed by Fluorescence in situ hybridization (FISH) analysis on leukocytes. Interestingly, array comparative genomic hybridization was normal in twin 2 but FISH analysis using the same probe as twin 1 showed mosaicism with one‐third of cells with a 2p25.3 deletion, one‐third of cells with a 2p25.3 duplication, and one‐third of normal cells. Genotyping with microsatellite markers confirmed the monozygosity of the twins. We propose that the chromosome imbalance may be due to a mitotic non‐allelic recombination occurring during blastomeric divisions of a normal zygote. Such event will result in three distinct cell populations, whose proportion in each embryo formed after separation from the zygote may differ, leading to discordant chromosomal anomalies between twins. We also discuss that the MYTL1L and the SNTG2 genes within the reported region could probably relate to the phenotypic discordance of the monozygotic twins.

Classical West "syndrome" phenotype with a subtelomeric 4p trisomy.

We report a girl with mild mental retardation with onset of infantile spasms at age of 9 months. Treatment with a short course of adrenocorticotropic hormone (ACTH) was successful. Initially, a diagnosis of idiopathic West syndrome, with good neurological outcome and disappearance of epilepsy after treatment, was made. Conventional karyotype was normal. Reinvestigations were done at age 8 years, because of a new pregnancy. Karyotyping of both parents was done because of mild dysmorphic features in the proband, and to eliminate other causes than early age epilepsy as the etiology of her mental retardation. Parental karyotypes showed a balanced paternal translocation (4p;17q) resulting in partial 4p trisomy, without significant 17q monosomy in the proband. Chromosomal abnormalities usually lead to a severe West syndrome with poor prognosis of neurological outcome (persistent severe epilepsy, mental retardation, and behavioral disturbances). The presence of an undetected cytogenetic anomaly in our proband with transient hypsarythmia is unusual and led us to propose systematic telomeric screening in apparently “idiopathic” West syndrome patients with mild mental retardation and subtle dysmorphic features.

Non-invasive prenatal testing for trisomy 21 based on analysis of cell-free fetal DNA circulating in the maternal plasma.

By‐the‐book implementation of non‐invasive prenatal test and clinical validation for trisomy 21.

Molecular cytogenetic characterization of a 4p15.1-pter duplication and a 4q35.1-qter deletion in a recombinant of chromosome 4 pericentric inversion†

To date, 10 cases of recombinant of chromosome 4 pericentric inversion involving sub‐bands p14p15 and q35 have been described. We report on the first case analyzed using array‐CGH in a female infant presenting psychomotor and growth retardation, facial anomalies, axial hypotonia, short neck, wide spaced nipples and cardiac defects. Conventional karyotype associated to FISH revealed a recombinant chromosome 4 with partial 4p duplication and 4q deletion derived from a paternal pericentric inversion. Array‐CGH allowed us to precise rec4 breakpoints: the proposita carried a small 4.82–4.97 Mb 4q35.1 terminal deletion and a large 35.3–36.7 Mb 4p15.1 terminal duplication. Duplications of the distal 2/3 of short arm of chromosome 4 give rise to recognizable craniofacial features but no specific visceral malformation. A contrario small terminal 4q deletions are associated with cardiac defects. This case and review of literature suggest that two genes ArgBP2 and PDLIM3, located at 4q35.1 and both involved in cardiac and muscle development, could be responsible for cardiac defects observed in terminal 4q35.1 deletions.

La CGH microarray : principe et applications en pathologie constitutionnelle

Chips technology has allowed to miniaturize process making possible to realize in one step and using the same device a lot of chemical reactions. The application of this technology to molecular cytogenetics resulted in the development of comparative genomic hybridization (CGH) on microarrays technique. Using this technique it is possible to detect very small genetic imbalances anywhere in the genome. Its usefulness has been well documented in cancer and more recently in constitutional disorders. In particular it has been used to detect interstitial and subtelomeric submicroscopic imbalances, to characterize their size at the molecular level or to define the breakpoints of translocation. The challenge today is to transfer this technology in laboratory medicine. Nevertheless this technology remains expensive and the existence of numerous sequence polymorphisms makes its interpretation difficult. Finally its is unlikely that it will make karyotyping obsolete as it does not allow to detect balanced rearrangements which after meiotic segregation might result in genome imbalance in the progeny.