Novel Compound Heterozygous Mutations in the Cathepsin K Gene in Japanese Female Siblings with Pyknodysostosis

Pycnodysostosis: Novel Variants in CTSK and Occurrence of Giant Cell Tumor

Pycnodysostosis is an autosomal recessive skeletal dysplasia caused by pathogenic variants in the cathepsin K ( CTSK ) gene. We report seven patients from four unrelated families with this condition in whom we have identified three novel pathogenic variants, c.120 + 1G > T in intron 2, c.399 + 1G > A in intron 4, and c.148T > G (p.W50G) in exon 2, and a known variant, c.568C > T (p.Q190*) in exon 5 of CTSK . We present the clinical, radiographic, and molecular findings of all individuals with molecularly proven pycnodysostosis from the present cohort. We also report the occurrence of giant cell tumor in the skull of a patient with this condition.

Molecular analysis of the CTSK gene in a cohort of 33 Brazilian families with pycnodysostosis from a cluster in a Brazilian Northeast region

Background

Pycnodysostosis is an autosomal recessive skeletal dysplasia, the prevalence of which is estimated to be low (1 per million). Nevertheless, in recent years we have found 27 affected individuals from 22 families in Ceará State, a region of the Brazilian Northeast, giving a local prevalence of 3 per million. This local prevalence associated with a high parental consanguinity, suggesting a possible founder effect, prompted us to perform a molecular investigation of these families to test this hypothesis.

Methods

The CTSK gene was sequenced by the Sanger method in the patients and their parents. In addition to 18 families from Ceará, this study also included 15 families from other Brazilian regions. We also investigated the origin of each family from the birthplace of the parents and/or grandparents.

Results

We have studied 39 patients, including 33 probands and 6 sibs, from 33 families with pycnodysostosis and identified six mutations, five previously described (c.436G>C, c.580G>A, c.721C>T, c.830C>T and c.953G>A) and one novel frameshift (c.83dupT). This frameshift variant seems to have a single origin in Ceará State, since the haplotype study using the polymorphic markers D1S2344, D1S442, D1S498 and D1S2715 suggested a common origin. Most of the mutations were found in homozygosity in the patients from Ceará (83.3 %) while in other states the mutations were found in homozygosity in half of patients. We have also shown that most of the families currently living outside of Ceará have northeastern ancestors, suggesting a dispersion of these mutations from the Brazilian Northeast.

Conclusions

The high frequency of pycnodysostosis in Ceará State is the consequence of the high inbreeding in that region. Several mutations, probably introduced a long time ago in Ceará, must have spread due to consanguineous marriages and internal population migration. However, the novel mutation seems to have a single origin in Ceará, suggestive of a founder effect.

Electronic supplementary material

The online version of this article (doi:10.1186/s40001-016-0228-7) contains supplementary material, which is available to authorized users.

Molecular and clinical analysis in a series of patients with Pyknodysostosis reveals some uncommon phenotypic findings

Pyknodysostosis is a rare autosomal recessive skeletal dysplasia characterized by short stature, deformity of the skull, osteosclerosis, hypoplasia of the clavicle, and bone fragility. Radiographs show increased bone density, osteosclerosis, and acroosteolysis of the terminal phalanges. The pycnodysostosis gene is located on chromosome 1q21 and encodes an enzyme called Cathepsin K. Cathepsin K is a cysteine protease lysosomal protein associated with the degradation of bone and cartilage. In the current study, the authors described the clinical, radiological and molecular features of a group of six Mexican patients, including two familial and two sporadic cases, with Pyknodysostosis. One of the patients presented hypoacusia, an unusual finding in this disease.