Longitudinal changes in height, weight and physical performance were studied in 33 Flemish male youth soccer players from the Ghent Youth Soccer Project. The players' ages at the start of the study ranged from 10.4 to 13.7 years, with a mean age of 12.2 +/- 0.7 years. Longitudinal changes were studied over a 5 year period. Peak height velocity and peak weight velocity were determined using non-smoothed polynomials. The estimations of peak height velocity, peak weight velocity and age at peak height velocity were 9.7 +/- 1.5 cm x year-1, 8.4 +/- 3.0 kg x year-1 and 13.8 +/- 0.8 years, respectively. Peak weight velocity occurred, on average, at the same age as peak height velocity. Balance, speed of limb movement, trunk strength, upper-body muscular endurance, explosive strength, running speed and agility, cardiorespiratory endurance and anaerobic capacity showed peak development at peak height velocity. A plateau in the velocity curves was observed after peak height velocity for upper-body muscular endurance, explosive strength and running speed. Flexibility exhibited peak development during the tear after peak height velocity. Trainers and coaches should be aware of the individual characteristics of the adolescent growth spurt and the training load should also be individualized at this time.

Data on six patients with a Pseudoxanthoma Elasticum (PXE)-like phenotype, characterized by excessive skin folding (resembling cutis laxa) and a deficiency of the vitamin K-dependent clotting factors (II, VII, IX, and X) are presented. A comparison is made between the clinical, ultrastructural, and molecular findings in these patients and those seen in classic PXE and cutis laxa, respectively. Clinical overlap with PXE is obvious from the skin manifestations of yellowish papules or leathery plaques with dot-like depressions at presentation, angioid streaks and/or ocular peau d'orange, and fragmentation and calcification of elastic fibers in the dermis. Important phenotypic differences with PXE include much more severe skin laxity with spreading toward the trunk and limbs with thick, leathery skin folds rather than confinement to flexural areas, and no decrease in visual acuity. Moreover, detailed electron microscopic analyses revealed that alterations of elastic fibers as well as their mineralization were slightly different from those in classic PXE. Molecular analysis revealed neither causal mutations in the ABCC6 gene (ATP-binding cassette subfamily C member 6), which is responsible for PXE, nor in VKORC1 (vitamin K 2,3 epoxide reductase), known to be involved in vitamin K-dependent factor deficiency. However, the GGCX gene (gamma-glutamyl carboxylase), encoding an enzyme important for gamma-carboxylation of gla-proteins, harbored mutations in six out of seven patients analyzed. These findings all support the hypothesis that the disorder indeed represents a separate clinical and genetic entity, the molecular background of which remains to be unraveled.

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Pseudoxanthoma elasticum (PXE) is a heritable connective tissue disorder characterized by ocular, cutaneous and cardiovascular manifestations. It is caused by mutations in the ABCC6 gene (chr. 16p13.1), encoding a transmembrane transporter protein, the substrate and biological function of which are currently unknown. A comprehensive clinical and molecular study of 38 Belgian PXE probands and 21 relatives (4 affected and 17 carriers) was performed. An extensive clinical evaluation protocol was implemented with serial fundus, skin and cardiovascular evaluation. We report on 14 novel mutations in the ABCC6 gene. We observed extensive variability in severity of both cutaneous and ocular lesions. The type of skin lesion however usually remained identical throughout the evolution of the disorder, while ophthalmological progression was mainly due to functional decline. Peripheral artery disease (53%) and stroke (15%) were significantly more prevalent than in the general population (10-30% and 0.3-0.5% respectively). Interestingly, we also observed a relatively high incidence of subclinical peripheral artery disease (41%) in our carrier population. We highlight the significance of peripheral artery disease and stroke in PXE patients as well as the subclinical manifestations in carriers. Through follow-up data we gained insight into the natural history of PXE. We propose a cost- and time-efficient two-step method of ABCC6 analysis which can be used in different populations. Additionally, we created a diagnostic flowchart and attempted to define the role of molecular analysis of ABCC6 in the work-up of a PXE patient.