A Case of the 7p22.2 Microduplication: Refinement of the Critical Chromosome Region for 7p22 Duplication Syndrome

7p22.2 Microduplication: A Pathogenic CNV?

Partial duplication of the short arm of chromosome 7 is a rare chromosome rearrangement. The phenotype spectrum associated with this rearrangement is extremely variable even if in the last decade the use of high-resolution microarray technology for the investigation of patients carrying this rearrangement allowed for the identification of the 7p22.1 sub-band causative of this phenotype and to recognize the corresponding 7p22.1 microduplication syndrome. We report two unrelated patients that carry a microduplication involving the 7.22.2 sub-band. Unlike 7p22.1 microduplication carriers, both patients only show a neurodevelopmental disorder without malformations. We better characterized the clinical pictures of these two patients providing insight into the clinical phenotype associated with the microduplication of the 7p22.2 sub-band and support for a possible role of this sub-band in the 7p22 microduplication syndrome.

Microdeletions and microduplications linked to severe congenital disorders in infertile men

Data on the clinical validity of DNA copy number variants (CNVs) in spermatogenic failure (SPGF) is limited. This study analyzed the genome-wide CNV profile in 215 men with idiopathic SPGF and 62 normozoospermic fertile men, recruited at the Andrology Clinic, Tartu University Hospital, Estonia. A two-fold higher representation of > 1 Mb CNVs was observed in men with SPGF (13%, n = 28) compared to controls (6.5%, n = 4). Seven patients with SPGF were identified as carriers of microdeletions (1q21.1; 2.4 Mb) or microduplications (3p26.3, 1.1 Mb; 7p22.3-p22.2, 1.56 Mb; 10q11.22, 1.42 Mb, three cases; Xp22.33; 2.3 Mb) linked to severe congenital conditions. Large autosomal CNV carriers had oligozoospermia, reduced or low-normal bitesticular volume (22-28 ml). The 7p22.3-p22.2 microduplication carrier presented mild intellectual disability, neuropsychiatric problems, and short stature. The Xp22.33 duplication at the PAR1/non-PAR boundary, previously linked to uterine agenesis, was detected in a patient with non-obstructive azoospermia. A novel recurrent intragenic deletion in testis-specific LRRC69 was significantly overrepresented in patients with SPGF compared to the general population (3.3% vs. 0.85%; χ² test, OR = 3.9 [95% CI 1.8-8.4], P = 0.0001). Assessment of clinically valid CNVs in patients with SPGF will improve their management and counselling for general and reproductive health, including risk of miscarriage and congenital disorders in future offspring.

Chromosome 9p terminal deletion in nine Egyptian patients and narrowing of the critical region for trigonocephaly

Background

This study aimed to delineate the clinical phenotype of patients with 9p deletions, pinpoint the chromosomal breakpoints, and identify the critical region for trigonocephaly, which is a frequent finding in 9p terminal deletion.

Methods

We investigated a cohort of nine patients with chromosome 9p terminal deletions who all displayed developmental delay, intellectual disability, hypotonia, and dysmorphic features. Of them, eight had trigonocephaly, seven had brain anomalies, seven had autistic manifestations, seven had fair hair, and six had a congenital heart defect (CHD).

Results

Karyotyping revealed 9p terminal deletion in all patients, and patients 8 and 9 had additional duplication of other chromosomal segments. We used six bacterial artificial chromosome (BAC) clones that could identify the breakpoints at 17–20 Mb from the 9p terminus. Array CGH identified the precise extent of the deletion in six patients; the deleted regions ranged from 16 to 18.8 Mb in four patients, patient 8 had an 11.58 Mb deletion and patient 9 had a 2.3 Mb deletion.

Conclusion

The gene deletion in the 9p24 region was insufficient to cause ambiguous genitalia because six of the nine patients had normal genitalia. We suggest that the critical region for trigonocephaly lies between 11,575 and 11,587 Mb from the chromosome 9p terminus. To the best of our knowledge, this is the minimal critical region reported for trigonocephaly in 9p deletion syndrome, and it warrants further delineation.

Cerebral folate transporter deficiency syndrome in three siblings: Why genetic testing for developmental and epileptic encephalopathies should be performed early and include the FOLR1 gene

Cerebral folate transporter deficiency syndrome, caused by FOLR-1 mutations is characterized by late infantile onset, severe developmental regression, epilepsy, and leukodystrophy. An extremely low concentration of 5-methyltetrahydrofolate in the cerebrospinal fluid provides a crucial clue to its diagnosis and is a treatment target. Oral or intravenous folinic acid (5-formyltetrahydrofolate) administration improves clinical symptoms and brain magnetic resonance imaging (MRI) findings. We describe three siblings carrying a novel homozygous FOLR1 nonsense mutation, that were referred due to intractable epilepsy and progressive neurological decline. Brain MRI showed hypomyelination and cerebellar atrophy. Folinic acid (oral and intravenous) supplementation, initiated after over 15 years illness, has failed to result in any sizeable clinical or neurophysiological improvement. Cerebral folate transport deficiency bears overlapping clinical features with many severe developmental encephalopathies. It is crucial to recognize FOLR1 signs and establish an early clinical and molecular diagnosis in order to provide timely folinic acid treatment and improve outcome.

Structure and Functions of Sidekicks

Many of the immunoglobulin superfamily (IgSF) molecules play pivotal roles in cell communication. The Sidekick (Sdk) gene, first described in Drosophila, encodes the single-pass transmembrane protein, Sdk, which is one of the largest among IgSF membrane proteins. Sdk first appeared in multicellular animals during the Precambrian age and later evolved to Sdk1 and Sdk2 in vertebrates by gene duplication. In flies, a single Sdk is involved in positioning photoreceptor neurons and their axons in the visual system and is responsible for dynamically rearranging cell shapes by strictly populating tricellular adherens junctions in epithelia. In vertebrates, Sdk1 and Sdk2 are expressed by unique sets of cell types and distinctively participate in the formation and/or maintenance of neural circuits in the retina, indicating that they are determinants of synaptic specificity. These functions are mediated by specific homophilic binding of their ectodomains and by intracellular association with PDZ scaffold proteins. Recent human genetic studies as well as animal experiments implicate that Sdk genes may influence various neurodevelopmental and psychiatric disorders, such as autism spectrum disorders, attention-deficit hyperactivity disorder, addiction, and depression. The gigantic Sdk1 gene is susceptible to erratic gene rearrangements or mutations in both somatic and germ-line cells, potentially contributing to neurological disorders and some types of cancers. This review summarizes what is known about the structure and roles of Sdks.

Inheritance of a Balanced t(12;20)(q24.33;p12.2) and Unbalanced der(13)t(7;13)(p21.3;q33.2) from a Maternally Derived Double Balanced Translocation Carrier

We report a 4-month-old male proband with a history of prominent forehead, hypertelorism, ear abnormalities, micrognathia, hypospadias, and multiple cardiac abnormalities. Initial microarray analysis detected a concurrent 7p21.3-p22.3 duplication and 13q33.2-q34 deletion indicating an unbalanced rearrangement. However, subsequent conventional cytogenetic studies only revealed what appeared to be a balanced t(12;20)(q24.33;p12.2). Fluorescence in situ hybridization (FISH) using chromosome-specific subtelomere probes confirmed the presence of an unbalanced der(13)t(7;13)(p21.3;q33.2) and balanced t(12;20)(q24.33;p12.2), both of maternal origin. In addition to our unique clinical findings, this case highlights the benefits and limitations of both conventional cytogenetic studies and microarray analysis and how FISH complements each methodology.