Genetic haploinsufficiency as a phenotypic determinant of a deletion 13q syndrome

Interstitial deletion of 13q14.13-q32.3 presenting with Arima syndrome and bilateral retinoblastoma

A patient with a large deletion of the distal part of the long arm of chromosome 13 showed severe psychomotor retardation, a characteristic face, nystagmus, retinopathy, cystic kidney disease, and brain malformation with molar tooth sign and cerebellar vermis hypoplasia, a phenotype typical of Arima syndrome. This patient also had bilateral retinoblastoma. Fluorescent in situ hybridization and single-nucleotide-polymorphism genotyping microarray demonstrated an interstitial deletion of 54 Mbp, ranging from 13q14.13 to 13q32.3 and involving the RB1 gene. This patient is the first case of Arima syndrome, or a Joubert syndrome-related disorder, that showed linkage to chromosome 13q.

Brain abnormalities on MR imaging in patients with retinoblastoma

BACKGROUND AND PURPOSE

Although pineoblastoma is the main brain abnormality associated with hereditary retinoblastoma, recent studies suggest an association with pineal cysts. This association is important because some pineoblastomas mimic pineal cysts. If there is a relationship, then radiologists should be aware of it because diagnostic confusion is possible. Mental retardation and congenital brain anomalies are also reported in patients with retinoblastoma, mostly in combination with 13q deletion syndrome. In this retrospective study, the presence of brain abnormalities on MR images in a large group of consecutive patients with retinoblastoma is evaluated.

MATERIALS AND METHODS

Brain MR images of 168 patients with retinoblastoma from 1989 to 2009 were evaluated by 2 radiologists for tumors, structural anomalies, myelinization, and coincidental findings. Clinical records were reviewed for laterality, heredity, and the presence of the 13q deletion syndrome.

RESULTS

The hereditary group (patients with bilateral and unilateral proved RB1-germline mutation) included 90 (54%) of 168 patients. Seven patients had 13q deletion syndrome. Normal findings on brain MR images were seen in 150 (89%) patients. Five pineoblastomas were detected, all in patients with hereditary retinoblastoma (5.5% in the hereditary subgroup). Nine pineal cysts were detected (2.2% in the hereditary subgroup). Corpus callosum agenesis was found in 1 patient and a Dandy-Walker variant in 1 patient, both in combination with 13q deletion syndrome.

CONCLUSIONS

Pineoblastoma is associated with hereditary retinoblastoma, and structural brain abnormalities are restricted to patients with the 13q deletion syndrome. The incidence of pineal cysts in patients with retinoblastomas is similar to that in healthy children and is not associated with hereditary retinoblastoma.

Phenotype and 244k array-CGH characterization of chromosome 13q deletions: an update of the phenotypic map of 13q21.1-qter

Partial deletions of the long arm of chromosome 13 lead to variable phenotypes dependant on the size and position of the deleted region. In order to update the phenotypic map of chromosome 13q21.1-qter deletions, we applied 244k Agilent oligonucleotide-based array-CGH to determine the exact breakpoints in 14 patients with partial deletions of this region. Subsequently, we linked the genotype to the patient's phenotype. Using this approach, we were able to refine the smallest deletion region linked to short stature (13q31.3: 89.5-91.6 Mb), microcephaly (13q33.3-q34), cortical development malformations (13q33.1-qter), Dandy-Walker malformation (DWM) (13q32.2-q33.1), corpus callosum agenesis (CCA) (13q32.3-q33.1), meningocele/encephalocele (13q31.3-qter), DWM, CCA, and neural tube defects (NTDs) taken together (13q32.3-q33.1), ano-/microphthalmia (13q31.3-13qter), cleft lip/palate (13q31.3-13q33.1), lung hypoplasia (13q31.3-13q33.1), and thumb a-/hypoplasia (13q31.3-q33.1 and 13q33.3-q34). Based on observations of this study and previous reports we suggest a new entity, "distal limb anomalies association," linked to 13q31.3q33.1 segment. Most of the individuals with deletion of any part of 13q21qter showed surprisingly similar facial dysmorphic features, and thus, a "13q deletion facial appearance" was suggested. Prominent nasal columella was mapped between 13q31.3 and 13q33.3, and micrognathia between 13q21.33 and 13q31.1. The degree of mental delay did not display a particular phenotype-genotype correlation on chromosome 13. In contrast to previous reports of carriers of 13q32 band deletions as the most seriously affected patients, we present two such individuals with long-term survival, 28 and 2.5 years.

Twelve new patients with 13q deletion syndrome: genotype-phenotype analyses in progress

13q deletion is characterized by a wide phenotypic spectrum resulting from a partial deletion of the long arm of chromosome 13. The main clinical features are mental retardation, growth retardation, craniofacial dysmorphy and various congenital defects. Only one recent Italian study was aimed at determining genotype-phenotype correlations among 13q deletions from a group of mainly live born children, using array-CGH and FISH. In order to improve the molecular characterization of 13q monosomy, 12 new patients (9 foetuses and 3 children) were collected based on a cohort of holoprosencephaly (HPE) linked to ZIC2 gene deletion and/or patients with 13q deletion diagnosed by standard karyotype. First, quantitative gene screening using MLPA (Multiplex Ligation dependent Probe Amplification) was performed to look for ZIC2 gene deletion and then, CGH array analysis was carried out using the Agilent Human Genome CGH microarray 4x44K (Agilent Technologies, Santa Clara, USA). All the foetuses had severe cerebral midline malformations associated with a deletion including the ZIC2 gene. We report one patient with Steinfeld phenotype linked to this chromosomal anomaly, and suggest that some of the associations between cerebral midline malformation and limb defects might be related to 13q deletion. Further candidate genes are suspected to explain the malformations associated with cerebral anomalies in the hypothesis of a contiguous gene syndrome: SPRY2 in 13q31.1 is implicated in lens cell proliferation and differentiation for congenital cataract; GPC5 in 13q32 is mainly expressed in the mesenchyme of the developing limb bud for upper limb anomalies.