ABSTRACT
Background@#Brachydactyly, a developmental disorder, refers to shortening of hands/feet due to small or missing metacarpals/metatarsals and/or phalanges. Isolated brachydactyly type E (BDE), characterized by shortened metacarpals and/or metatarsals, consists in a small proportion of patients with Homeobox D13 (HOXD13) or parathyroid-hormone-like hormone (PTHLH) mutations. BDE is often accompanied by other anomalies that are parts of many congenital syndromes. In this study, we investigated a Chinese family presented with BDE combined with pectus carinatum and short stature.@*Methods@#A four-generation Chinese family was recruited in June 2016. After informed consent was obtained, venous blood was collected, and genomic DNA was extracted by standard procedures. Whole-exome sequencing was performed to screen pathogenic mutation, array comparative genomic hybridization (Array-CGH) analysis was used to analyze copy number variations, and quantitative real-time polymerase chain reaction (PCR), stride over breakpoint PCR (gap-PCR), and Sanger sequencing were performed to confirm the candidate variation.@*Results@#A 3.06-Mb deletion (chr12:25473650–28536747) was identified and segregated with the phenotype in this family. The deletion region encompasses 23 annotated genes, one of which is PTHLH which has been reported to be causative to the BDE. PTHLH is an important regulator of endochondral bone development. The affected individuals showed bilateral, severe, and generalized brachydactyly with short stature, pectus carinatum, and prematurely fusion of epiphyses. The feature of pectus carinatum has not been described in the PTHLH-related BDE patients previously.@*Conclusions@#The haploinsufficiency of PTHLH might be responsible for the disease in this family. This study has expanded the knowledge on the phenotypic presentation of PTHLH variation.
ABSTRACT
BACKGROUND: Autosomal-dominant brachydactyly type E is a congenital abnormality characterized by small hands and feet, which is a consequence of shortened metacarpals and metatarsals. We recently encountered a young gentleman exhibiting shortening of 4th and 5th fingers and toes. Initially, we suspected him having pseudopseudohypoparathyroidism (PPHP) because of normal biochemical parameters, including electrolyte, Ca, P, and parathyroid hormone (PTH) levels; however, his mother and maternal grandmother had the same conditions in their hands and feet. Furthermore, his mother showed normal biochemical parameters. To the best of our knowledge, PPHP is inherited via a mutated paternal allele, owing to the paternal imprinting of GNAS (guanine nucleotide binding protein, alpha stimulating) in the renal proximal tubule. Therefore, we decided to further analyze the genetic background in this family. METHODS: Whole exome sequencing was performed using genomic DNA from the affected mother, son, and the unaffected father as a negative control. RESULTS: We selected the intersection between 45,490 variants from the mother and 45,646 variants from the son and excluded 27,512 overlapping variants identified from the father. By excluding homogenous and compound heterozygous variants and removing all previously reported variants, 147 variants were identified to be shared by the mother and son. Variants that had least proximities among species were excluded and finally 23 variants remained. CONCLUSION: Among them, we identified a defect in parathyroid hormone like hormone (PTHLH), encoding the PTH-related protein, to be disease-causative. Herein, we report a family affected with brachydactyly type E2 caused by a novel PTHLH mutation, which was confused with PPHP with unclassical genetic penetrance.