Two siblings with alternate unbalanced recombinants derived from a large cryptic maternal pericentric inversion of chromosome 20

Short report: Twins with 20p13 duplication. Case report and comprehensive literature review

BACKGROUND

Trisomy 20p is a rare genetic condition caused by a duplication of the short arm of chromosome 20.

METHODS

We employed clinical observation and molecular genetic testing (SNP microarray), to study identical twin males with an unknown dysmorphic syndrome. We conducted a literature review of trisomy 20p and collated the clinical and molecular genetic findings on 20 affected subjects reported since 2000.

RESULTS

Identical twin males, whose prenatal course was complicated by a twin-to-twin transfusion, manifested profound language and neurocognitive delays as well as distinctive facial dysmorphisms when evaluated at 2 years of age. SNP microarray identified identical duplications of 20p13 with no other chromosomal aberrations. A literature survey of 20p trisomy syndrome identified 20 other examples of this condition reported since 2000, which we collated with 33 summarized by Sidwell et al. (2000). Within the combined total of 55 affected individuals, we found a distinctive clinical phenotype that provides insight on the effects of abnormal dosage of genes in 20p13. These loci include FAM110A (OMIM 611393), ANGPT4 (OMIM 603705), RSPO4 (OMIM 610573), PSMF1 (OMIM 617858), SNPH (OMIM 604942), SDCBP2 (OMIM 617358), FKBP1A (OMIM 186945), TMEM74B, C20orf202, and RAD21L1 (OMIM 619533). Gene profiling highlighted that syntaphilin (SNPH) is highly expressed in mammalian brain, where it is considered critical for mitochondrial transport in neuronal axons, and to directly influence axonal morphogenesis and function.

CONCLUSION

We propose that abnormal activity of syntaphilin engendered by the trisomy is primarily responsible for the language, neurocognitive, and gross motor delays reported in individuals with 20p trisomy. Additional studies, for example, characterization of cerebral organoids generated from affected patients may help to better understand this condition, and potentially suggest rational remedies to improve the lives of affected individuals and their families.

A novel de novo 20q13.32-q13.33 deletion in a 2-year-old child with poor growth, feeding difficulties and low bone mass

Interstitial deletions of the long arm of chromosome 20 are rarely reported in the literature. We report a 2-year-old child with a 2.6 Mb deletion of 20q13.32-q13.33, detected by microarray-based comparative genomic hybridization, who presented with poor growth, feeding difficulties, abnormal subcutaneous fat distribution with the lack of adipose tissue on clinical examination, facial dysmorphism and low bone mass. This report adds to rare publications describing constitutional aberrations of chromosome 20q, and adds further evidence to the fact that deletion of the GNAS complex may not always be associated with an Albright's hereditary osteodystrophy phenotype as described previously.

Duplication of 20qter and deletion of 20pter due to paternal pericentric inversion: patient report and review of 20qter duplications

Duplications of the terminal long arm of chromosome 20 are rare chromosomal anomalies. We report a male infant found on array comparative genomic hybridization analysis to have a 19.5 Mb duplication of chromosome 20q13.12-13.33, as well as an 886 kb deletion of 20p13 at 18,580-904,299 bp. This anomaly occurred as the recombinant product of a paternal pericentric inversion. There have been 23 reported clinical cases involving 20qter duplications; however, to our knowledge this is only the second reported patient with a paternal pericentric inversion resulting in 46,XY,rec(20)dup(20q). This patient shares many characteristics with previously described patients with 20qter duplications, including microphthalmia, anteverted nares, long ears, cleft palate, small chin, dimpled chin, cardiac malformations, and normal intrauterine growth. While there is variable morbidity in patients with terminal duplications of 20q, a review of previously reported patients and comparison to our patient's findings shows significant phenotypic similarity.

Combined immunodeficiency in a 3-year-old boy with 16p11.2 and 20p12.2-11.2 chromosomal duplications

We report for the first time on a 3-year-old boy with paternally inherited 212.85 kb-16p11.2 and 7.8 Mb-20p12.2-11.23 interstitial microduplications associated with having congenital cardiac defect, dysmorphic facial features, and combined T-, B-, and NK cell immunodeficiency. In addition the 7.8 Mb-20p12.2-11.23 microduplication is unique showing novel breakpoints among all partial trisomy/duplication 20p reported to date, narrowing down the critical region for trisomy 20p syndrome.

A case of partial trisomy 20p resulting from meiotic recombination of a maternal pericentric inversion

Here we report the cytogenetic and clinical manifestations observed in a patient with a rec(20)dup(20p)inv(20)(p11.2q13.3)mat. The patient was a full-term newborn girl with asymmetric intrauterine growth restriction and multiple congenital malformations, including a ventricular septal defect, pulmonary atresia, ambiguous genitalia, clinodactyly, and sacral dimpling. To our knowledge, this is the 4th report in the world and the 1st one in Korea of a patient with rec(20)dup(20p).

A genotype-first approach for the molecular and clinical characterization of uncommon de novo microdeletion of 20q13.33

Background

Subtelomeric deletions of the long arm of chromosome 20 are rare, with only 11 described in the literature. Clinical features of individuals with these microdeletions include severe limb malformations, skeletal abnormalities, growth retardation, developmental and speech delay, mental retardation, seizures and mild, non-specific dysmorphic features.

Methodology/Principal Findings

We characterized microdeletions at 20q13.33 in six individuals referred for genetic evaluation of developmental delay, mental retardation, and/or congenital anomalies. A comparison to previously reported cases of 20q13.33 microdeletion shows phenotypic overlap, with clinical features that include mental retardation, developmental delay, speech and language deficits, seizures, and behavior problems such as autistic spectrum disorder. There does not appear to be a clinically recognizable constellation of dysmorphic features among individuals with subtelomeric 20q microdeletions.

Conclusions/Significance

Based on genotype-phenotype correlation among individuals in this and previous studies, we discuss several possible candidate genes for specific clinical features, including ARFGAP1, CHRNA4 and KCNQ2 and neurodevelopmental deficits. Deletion of this region may play an important role in cognitive development.