A new locus in chromosome 2q37-qter is associated with posterior polar cataract

Novel 4.18 Mb deletion resulting in 2q37 microdeletion syndrome combined with PTH resistance found in one Chinese patient

BACKGROUND

2q37 microdeletion syndrome is a rare clinical condition characterized by a series of physical abnormalities. Its Albright hereditary osteodystrophy (AHO)-like manifestations and possible complication of biochemical abnormalities indicating PTH resistance greatly increased the likelihood of misdiagnosis with classic pseudohypoparathyroidism (PHP) caused by GNAS mutation or methylation alteration, even though there have only been six reports of such clinical occasions.

PURPOSE

to investigate the underlying genetic defect in a male patient presenting hypocalcemia, elevated PTH and with a history of kyphosis.

METHOD

clinical information was collected, while the DNA was extracted from peripheral blood and subjected to methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) and exome sequencing.

RESULT

Physical characteristics featuring short stature, obesity, round face, short neck, and shortened 4th metacarpal and laboratory examination of the patient suggested the presence of PTH resistance, which is indicative of PHP. MS-MLPA did not reveal methylation alterations or deletions of GNAS, STX16 or other monogenetic alterations responsible for iPPSDs, but WES revealed a long-range deletion of approximately 4.18 Mb of the 2q37 region that spanned AGAP1 to NDUFA10, indicating that the patient had 2q37 microdeletion syndrome with PTH resistance.

CONCLUSION

After undergoing MS-MLPA and exome sequencing, a novel deletion spanning 4.18 Mb on the 2q37 region was identified in one male patient, clarifying the diagnosis of 2q37 microdeletion syndrome with PTH resistance. The new genetic discovery added to our understanding of the molecular defects that cause inactivating PTH/PTH-related protein signaling disorders (iPPSDs).

Whole Exome Sequencing of 20 Spanish Families: Candidate Genes for Non-Syndromic Pediatric Cataracts

Non-syndromic pediatric cataracts are defined as opacification of the crystalline lens that occurs during the first years of life without affecting other organs. Given that this disease is one of the most frequent causes of reversible blindness in childhood, the main objective of this study was to propose new responsible gene candidates that would allow a more targeted genetic approach and expand our genetic knowledge about the disease. We present a whole exome sequencing (WES) study of 20 Spanish families with non-syndromic pediatric cataracts and a previous negative result on an ophthalmology next-generation sequencing panel. After ophthalmological evaluation and collection of peripheral blood samples from these families, WES was performed. We were able to reach a genetic diagnosis in 10% of the families analyzed and found genes that could cause pediatric cataracts in 35% of the cohort. Of the variants found, 18.2% were classified as pathogenic, 9% as likely pathogenic, and 72.8% as variants of uncertain significance. However, we did not find conclusive results in 55% of the families studied, which suggests further studies are needed. The results of this WES study allow us to propose LONP1, ACACA, TRPM1, CLIC5, HSPE1, ODF1, PIKFYVE, and CHMP4A as potential candidates to further investigate for their role in pediatric cataracts, and AQP5 and locus 2q37 as causal genes.

A novel HSF4 gene mutation causes autosomal-dominant cataracts in a Chinese family

Congenital cataracts are a significant cause of visual impairment or blindness in children. One-third of cases estimated to have a genetic cause. We carried out gene analysis and bioinformatics analysis to map the locus and to identify the underlying genetic defect in a 12-member, four-generation Chinese family affected with bilateral congenital cataracts. We screened individuals of the family and discovered a distinct missense mutation in HSF4 (a gene at this locus that encodes teat-shock transcription factor 4). Bioinformatics analysis was used to determine possible changes in the protein structure that could affect the phenotype. Sequencing of the candidate genes showed a heterozygous c.69 G→T change in the heat shock transcription factor 4 (HSF4) gene, which resulted in the substitution of a lysine with an asparagine (p. K23N). This mutation cosegregated with all affected individuals and was not observed in unaffected family members. Bioinformatics analysis indicated that the p. K23N mutation was predicted to be disease causing. This is the first report of the novel missense mutation, c.69 G→T (p. K23N), in exon 3 of the HSF4 locus on 16q21-q22 associated with bilateral congenital cataracts in a Chinese family. This novel mutation could enable propergenetic diagnostics and counseling in affected families and could lead to a better understanding of the structure and function of HSF4 in health and disease.