Mosaic 13q13.2-ter deletion restricted to tissues of ectodermal and mesodermal origins

Mosaicism for structural non-centromeric autosomal rearrangements in disease-defined carriers: sex differences in the rearrangements profile and maternal age distributions

Background

Mosaicism for an autosomal structural rearrangement (Rea) associated with clinical manifestation of chromosomal imbalance is rare. Consequently, there is a lack of basic epidemiological characterization of this kind of mosaicism, such as population rate, cytogenetic profile of Reas involved, maternal age distribution, and sex (male to female) ratio among Rea carriers. The objectives of the present study were: (i) determination of the Rea profile in clinically affected individuals, (ii) comparative analysis of the cytogenetic profile and involvement of single chromosomes to rearrangements in affected and previously reported asymptomatic carriers, (iii) analysis of the male/female ratio in carriers of various types of Rea, and, (iv) examination of parental ages distributions according to carriers’ sex.

Results

Two hundred and forty six disease-defined cases of mosaicism for autosomal non-centromeric Rea with a normal cell line of known sex were identified from the literature. There was a significant difference in single chromosome involvements compared to structural rearrangements between affected and asymptomatic carriers of unbalanced Rea, p =0.0030. In affected carriers, chromosome 18 was most frequently involved in structural rearrangements (12.6% of 246 instances). The least frequently rearranged were chromosomes 16 and 21 (0.8% and 1.2%, respectively). In asymptomatic carriers, the most frequently rearranged were chromosomes 5 and 21 (13% of 51 instances each). Among carriers of “loss” or “gain/loss” of genomic material, a female predominance was observed (50 M/89 F, different from population ratio of 1.06 at p = 0.0002). Carriers of either “gain” or balanced Rea demonstrated typical male predominance (41 M/30 F and 18 M/16 F), not different from 1.06. Maternal and paternal ages were reported in 129 and in 109 cases, respectively. There was a significant difference in maternal age distribution between male and female carriers, with mean maternal age of 25.2 years vs 28.3 years (p = 0.032). However, there was no difference in paternal age, with mean paternal age of 29.4 in both groups.

Conclusion

The data suggested that structural rearrangements of certain chromosomes involved in mosaicism may not be tolerated by the embryo, while others have higher survival prospects. Maternal age appears to be a risk factor for somatic mosaicism of structural Rea in female offspring or might cause an adverse effect on male embryo viability.

Electronic supplementary material

The online version of this article (doi:10.1186/s13039-017-0321-9) contains supplementary material, which is available to authorized users.

Tissue-limited mosaicism for monosomy 13

Karyotypic discordance between different tissues in an individual is uncommon. We report on a patient with multiple congenital anomalies and mosaicism for monosomy 13 limited to fibroblasts. Findings include microcephaly, agenesis of the corpus callosum, bilateral posterior colobomas, cataract and optic nerve dysplasia, patent foramen ovale, renal hypoplasia, hypospadias and unilateral inguinal hernia, unilateral hypoplasia of the lower limb, sparse and patchy hair, subtle pigmentary mosaicism, and global developmental delay. The lymphocyte karyotype was normal, whereas the fibroblast karyotype showed mosaicism for a del(13)(q11→ter). Review of the literature identified three previous reports of similar patients with multiple congenital anomalies, normal lymphocyte karyotype, and subsequent, diagnostic fibroblast karyotyping. Comparison of the previously reported patients with the patient reported here defines a common phenotype for tissue-limited mosaicism for monosomy 13 consisting of prenatal-onset growth deficiency; microcephaly; facial abnormalities including prominent nasal bridge, hypertelorism, ptosis, epicanthal folds, microphthalmia, coloboma, retinoblastoma, prominent maxilla, micrognathia, and low-set ears; limb abnormalities including small to absent thumbs, clinodactyly of fifth finger, fused metacarpal bones 4 and 5, talipes equinovarus, and short first toe; cardiac defect; renal anomalies; and genitalia abnormalities including hypospadias and cryptorchidism. In conclusion, this case further emphasizes that fibroblast karyotyping should be employed when the diagnosis remains unclear, especially in the presence of pigmentary mosaicism or segmental hypoplasia.

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.

Uveal coloboma: clinical and basic science update

PURPOSE OF REVIEW

To integrate knowledge on the embryologic and molecular basis of optic fissure closure with clinical observations in patients with uveal coloboma.

RECENT FINDINGS

Closure of the optic fissure has been well characterized and many genetic alterations have been associated with coloboma; however, molecular mechanisms leading to coloboma remain largely unknown. In the past decade, we have gained better understanding of genes critical to eye development; however, mutations in these genes have been found in few individuals with coloboma. CHD7 mutations have been identified in patients with CHARGE syndrome (coloboma, heart defects, choanal atresia, retarded growth, genital anomalies, and ear anomalies or deafness). Animal models are bringing us closer to a molecular understanding of optic fissure closure.

SUMMARY

Optic fissure closure requires precise orchestration in timing and apposition of two poles of the optic cup. The relative roles of genetics and environment on this process remain elusive. While most cases of coloboma are sporadic, autosomal dominant, autosomal recessive, and X-linked inheritance patterns have been described. Genetically, colobomata demonstrate pleiotropy, heterogeneity, variable expressivity, and reduced penetrance. Coloboma is a complex disorder with a variable prognosis and requires regular examination to optimize visual acuity and to monitor for potential complications.