Molecular cytogenetic characterization of a 2q35-q37 duplication and a 4q35.1-q35.2 deletion in two cousins: A genotype-phenotype analysis

Ocular and Systemic Anomalies in an Infant With 4q Deletion and 3q Duplication: Case Report and Review of Literature

This is a case report of a female infant with two rare pathogenic chromosomal abnormalities: partial trisomy of chromosome 3 (3q25.2 to 3q29) and partial monosomy of chromosome 4 (4q34.1 to 4q35.2). A comprehensive evaluation and literature review revealed ocular and systemic malformations not previously described in association with either chromosomal aberration. Comparative genomic hybridization was performed to confirm the chromosomal abnormalities. A thorough literature search was conducted to contextualize the findings within existing knowledge of similar chromosomal aberrations. Genetic analysis revealed an unbalanced translocation between the long arms of chromosomes 3 and 4, resulting in partial trisomy of chromosome 3 (3q25.2 to 3q29) and partial monosomy of chromosome 4 (4q34.1 to 4q35.2). Ocular anomalies included nystagmus, epicanthus, lagophthalmos, entropion, megalocornea, corneal clouding, infantile glaucoma, high myopia, and retinal hyperpigmentation. The patient would undergo bilateral lower eyelid rotation and gonioscopy-assisted transluminal trabeculectomy procedures in the management of her congenital malformations. The distinct ophthalmic abnormalities observed represent novel features within the spectrum of partial trisomy three and partial monosomy four at the specified breakpoints. The literature search unveiled the previously documented features associated with genetic translocation and confirmed various novel features specific to our patient's phenotype. Further research will be essential to elucidate the genetic mechanisms underlying these ocular manifestations and their implications for the clinical management of cases. [J Pediatr Ophthalmol Strabismus. 2024;61(6):e66-e74.].

Melatonin receptor 1A variants as genetic cause of idiopathic osteoporosis

Idiopathic osteoporosis (IOP) is a rare form of early-onset osteoporosis diagnosed in patients with no known metabolic or hormonal cause of bone loss and unknown pathogenesis. Patients with IOP commonly report both childhood fractures and family history of osteoporosis, raising the possibility of genetic etiologies of IOP. Whole-exome sequencing analyses of different IOP cohorts identified multiple variants in melatonin receptor 1A (MTNR1A) with a potential pathogenic outcome. A rare MTNR1A variant (rs374152717) was found in members of an Ashkenazi Jewish family with IOP, and an MTNR1A variant (rs28383653) was found in a nonrelated female IOP cohort (4%). Both variants occur at a substantially higher frequency in Ashkenazi Jewish individuals than in the general population. We investigated consequences of the heterozygous (rs374152717) variant [MTNR1Ac.184+1G>T (MTNR1Ac.184+1G>T)] on bone physiology. A mouse model of the human rs374152717 variant reproduced the low bone mass (BM) phenotype of young-adult patients with IOP. Low BM occurred because of induction of senescence in mutant osteoblasts followed by compromised differentiation and function. In human cells, introduction of rs374152717 led to translation of a nonfunctional protein and subsequent dysregulation of melatonin signaling. These studies provide evidence that MTNR1A mutations entail a genetic etiology of IOP and establish the rs374152717 variant as a loss-of-function allele that impairs bone turnover by inducing senescence in osteoblasts. The higher prevalence of the MTNR1A variants identified in IOP cohorts versus the general population indicates a greater risk of IOP in those carrying these variants, especially Ashkenazi Jewish individuals bearing the rs374152717 variant.

Distal 2q duplication in a patient with intellectual disability

We report on a patient with a distal 16.4-Mb duplication at 2q36.3-qter, who presented with severe intellectual disability, microcephaly, brachycephaly, prominent forehead, hypertelorism, prominent eyes, thin upper lip, and progenia. Copy number analysis using whole exome data detected a distal 2q duplication. This is the first report describing a distal 2q duplication at the molecular level.

Recurrence of an early postzygotic rescue of an inherited unbalanced translocation resulting in mosaic segmental uniparental isodisomy of chromosome 11q in siblings

Balanced translocations are associated with a risk of transmission of unbalanced chromosomal rearrangements in the offspring. Such inherited chromosomal abnormalities are typically non-mosaic as they are present in the germline. We report the recurrence in two siblings of a mosaicism for a chromosomal rearrangement inherited from their asymptomatic father who carried a balanced t(2;11)(q35;q25) translocation. Both siblings exhibited a similar phenotype including intellectual disability, dysmorphic features, kyphoscoliosis, and cervical spinal stenosis. Karyotyping, fluorescence in situ hybridization and SNP array analysis of blood lymphocytes of both siblings identified two cell lines: one carrying a 2q35q37.3 duplication and a 11q25qter deletion (~90% cells), and one carrying an 11q uniparental isodisomy of maternal origin (~10% cells). We hypothesize that these mosaics were related to a postzygotic rescue mechanism which unexpectedly recurred in both siblings.

Report of trisomy 2q34-qter and monosomy 4q35.2-qter in a child with mild dysmorphic syndrome and karyotype 46,XY,der(4)t(2;4)(q34;q35.2)pat

Background

Concomitant trisomy 2q3 and monosomy 4q3 have been rarely reported. Pure trisomy 2q3 has been associated with microcephaly, hypertelorism, low-set ears, micrognathia, visceral abnormalities, and growth retardation. Monosomy 4q3 includes a wide variety of dysmorphic features such an abnormal skull shape, hypertelorism, Pierre Robin sequence, short nose with abnormal bridge, fifth finger clinodactyly, congenital heart, and genitourinary defects, in addition to intellectual disability, developmental delay, and hypotonia, but more distal deletions involving 4q34-qter may result in milder phenotypes. Here, we present a child with a mild dysmorphic syndrome, resulted of a duplication 2q34-qter and a deletion 4q35.2-qter inherited of his father.

Case presentation

We report a child, who at birth presented hypotonia, dysmorphism, and bilateral cryptorchidism. At 2 years and 9 month of age he showed brachycephaly, narrow forehead, bilateral frontoparietal hypertrichosis, down slanting palpebral fissures, sparse eyebrows, sparse short eyelashes, hypertelorism, depressed nasal root, broad nasal bridge, bulbous nasal tip, prominent colummela, broad nasal ala, smooth filtrum, high arched palate, thin upper lips, and ears rotated backwards. He also showed telethelia, hypertrichosis from dorsal to the sacral region, hands with clinodactyly and hypoplasia of the terminal phalanx of the fifth finger, and broad thumbs, broad first toes, and right cryptorchidism. A chromosomal study revealed a karyotype 46,XY,der(4)t(2;4)(q34;q35.2), while an array comparative genomic hybridization showed a 31.12 Mb duplication of the chromosome 2q34-q37.3 and a 1.49 Mb deletion in the chromosome 4q35.2.

Conclusions

To our knowledge, only four families with translocation t(2;4) have been reported, two of them involving t(2q;4q), but the breakpoints involved in our patient have not been previously observed. The genomic imbalance in this patient was a duplication of 318 genes of the region 2q34-q37.3 and a deletion of 7 genes of 4q35.2. We discuss difficulty to assign specific congenital abnormalities to these duplicated/deleted regions and include some cases with terminal deletions of 4q with normal or just mildly detectable phenotypic effects.