Nail-Patella Syndrome is also known as Iliac Horn Syndrome, Hereditary Onychoostedysplasia, Fong Disease or Turner-Kiser Syndrome. It is a rare multisystem genetic disorder.
Incidence, Epidemiology, and Genetic
The incidence of NPS is about 2-3/100.000 births and it haven’t any ethnic prevalence. Inheritance occurs as an autossomal dominant trait linked to ABO blood group locus. The risk of transmitting the disorder from affected parent to offspring is 50% , regardless of the sex of the child, with females being affected 10% more often.
It is already determined that an abnormality on chromosome 9q34 is involved with NPS , but the exact gene is not identified yet.
The complete pathophysiology underlying NPS is not known. Probably, the musculoskeletal abnormalities are involved with synthesis, assembly, or degradation collagen disorder.
Renal histology changes by light microscopy are nonspecific, with localized thickening of the capillary wall. Focal glomerular deposits of IgM and C3 may occur. The characteristic ultrastructural changes are localized areas of rarefaction of the glomerular basement membrane, with intramembranous deposits having the appearance and periodicity of collagen.
Signs & Symptoms
There isn’t a exact period to presentation of NPS signs and symptoms, although it is much more common during childhood. They can be identify in two different systems :
Nails. They are dystrophic in 80-90% of all NPS. Frequently , nails are absent , but when they are present some abnormalities can be found: discolored nails, koilonychia, longitudinal ridges, triangular lunulae. Changes are often symmetric. Fingernails are the most frequently affected, specially the thumbnails.
Knees Patella is absent or hypoplastic in 60% of all NPS. A lateral displacement on knee flexion (knock-knee deformity) can be found. Often it is associated with osteoarthritis , osteoarthrosis, and knee effusions.
Elbows Abnormalities aren’t so common , but aplasia , hypoplasia, posterior process at distal ends of humerus with a increased carrying angle with limited extension and suppination.
Pelvis Iliac bone may also have horns or spurs, only detected by x-ray, which are pathognomonic of NPS.
Renal problems were thought to be present in 50% of all NPS. Due to the high incidence of renal diseases, like renal stones, in general population this number was possibly over calculated. Latter studies shown that about 10% of all NPS have actually renal disease.
Major Renal Manifestations are microscopic hematuria, minimal or nephrotic proteinuria, edema ,and hypertension.
Minor Renal Manifestations are renal stones and congenital malformations as vesicoureteral reflux, atrophy, hypoplasia, and duplications.
Complications from renal manifestations include nephrotic and nephritic syndrome , and chronic renal failure.
It must include:
Urinalysis - Hematuria, proteinuria. Microscopy with a glomerular pattern : damage RBC’s and RBC casts.
Renal Biopsy - On light microscopy, variable from normal to basement membrane thickening to complete or segmental glomerulosclerosis. On Electronic microscopy the "moth-eaten" appearance is pathognomonic.
Skeletal X-ray- Iliac Horns, hypoplastic or absent patella, abnormal radio-ulnar articulation, and hypoplastic radial heads.
Treatment and Prognosis
There isn’t treatment for underlying disorder. Management must be done in order to prevent and treat the renal complications. A multidisciplinary approach must be done , including Pediatrics, Nephrology, Orthopedics, Rheumatology, and Psychology. Prognosis is usually benign although 10% of all NPS develop end-stage renal failure and the introduction of dialysis and renal transplantation is necessary.