Further delineation of spondylometaphyseal dysplasia with cone-rod dystrophy

Mutations in PCYT1A cause spondylometaphyseal dysplasia with cone-rod dystrophy

Spondylometaphyseal dysplasia with cone-rod dystrophy is a rare autosomal-recessive disorder characterized by severe short stature, progressive lower-limb bowing, flattened vertebral bodies, metaphyseal involvement, and visual impairment caused by cone-rod dystrophy. Whole-exome sequencing of four individuals affected by this disorder from two Brazilian families identified two previously unreported homozygous mutations in PCYT1A. This gene encodes the alpha isoform of the phosphate cytidylyltransferase 1 choline enzyme, which is responsible for converting phosphocholine into cytidine diphosphate-choline, a key intermediate step in the phosphatidylcholine biosynthesis pathway. A different enzymatic defect in this pathway has been previously associated with a muscular dystrophy with mitochondrial structural abnormalities that does not have cartilage and/or bone or retinal involvement. Thus, the deregulation of the phosphatidylcholine pathway may play a role in multiple genetic diseases in humans, and further studies are necessary to uncover its precise pathogenic mechanisms and the entirety of its phenotypic spectrum.

Axial spondylometaphyseal dysplasia: additional reports

Axial spondylometaphyseal dysplasia (SMD) (OMIM 602271) is an uncommon skeletal dysplasia characterized by metaphyseal changes of truncal-juxtatruncal bones, including the proximal femora, and retinal abnormalities. The disorder has not attracted much attention since initially reported; however, it has been included in the nosology of genetic skeletal disorders [Warman et al. (2011); Am J Med Genet Part A 155A:943-968] in part because of a recent publication of two additional cases [Isidor et al. (2010); Am J Med Genet Part A 152A:1550-1554]. We report here on the clinical and radiological manifestations in seven affected individuals from five families (three sporadic cases and two familial cases). Based on our observations and Isidor's report, the clinical and radiological hallmarks of axial SMD can be defined: The main clinical findings are postnatal growth failure, rhizomelic short stature in early childhood evolving into short trunk in late childhood, and thoracic hypoplasia that may cause mild to moderate respiratory problems in the neonatal period and later susceptibility to airway infection. Impaired visual acuity comes to medical attention in early life and function rapidly deteriorates. Retinal changes are diagnosed as retinitis pigmentosa or pigmentary retinal degeneration on fundoscopic examination and cone-rod dystrophy on electroretinogram. The radiological hallmarks include short ribs with flared, cupped anterior ends, mild spondylar dysplasia, lacy iliac crests, and metaphyseal irregularities essentially confined to the proximal femora. Equally affected sibling pairs of opposite gender and parental consanguinity are strongly suggestive of autosomal recessive inheritance.

Spondylometaphyseal dysplasia with cone-rod dystrophy

The co-occurrence of skeletal dysplasia and ophthalmologic abnormality is extremely rare. We report on a boy of a unique form of spondylometaphyseal dysplasia associated with cone-rod dystrophy. He presented with postnatal severe short stature, progressive lower limb deformity with rhizomelic shortening of the long bones, prominent joints with limited mobility in knees and elbows, mild thoracic scoliosis, and vision impairment due to cone dystrophy. Correction of deformity and simultaneous limb lengthening was performed in bilateral femora and tibiae without major complications. Skeletal manifestations in addition to comprehensive ophthalmologic examinations were described in this patient who had been followed from infancy to 16 years of age.

Spondylometaphyseal dysplasia with cone-rod dystrophy

PURPOSE

To report on the clinical ophthalmologic and radiographic findings in spondylometaphyseal dysplasia with cone-rod dystrophy.

BACKGROUND

The spondylometaphyseal dysplasias are a rare and heterogeneous group of disorders characterized by skeletal abnormalities of the spine and the metaphyses of long bones. In rare instances, spondylometaphyseal dysplasia can occur concomitantly with ocular abnormalities including a retinal degeneration of the cone-rod dystrophy type.

METHODS

Retrospective review of affected twin females with serial radiographic imaging, comprehensive ophthalmologic examination, fundus photography, and electroretinography.

RESULTS

The major radiographic findings involved bony abnormalities of the spine, metaphyses of the long bones and a distinctive shape to the bony pelvis. Both twins had a fine nystagmus that was present by 10 months of age. Dilated ocular fundus examination revealed similar appearing bilateral, large, excavated, well-circumscribed oval areas of chorioretinal atrophy occupying the macula between the aracades. Electroretinography showed a significant reduction in the photopic responses and slight reduction in the scotopic component of the waveforms consistent with cone-rod dystrophy.

CONCLUSIONS

Spondylometaphyseal dysplasia with cone-rod dystrophy is a rare congenital disorder of unknown inheritance pattern and pathophysiolgy. The ocular manifestations appear to stabilize in early adolescence whereas the skeletal abnormalities are progressive with age.