Nail-Patella syndrome (NPS) also known as hereditary osteo-onychodysplasia is a rare genetic disorder inherited through autosomal dominance that causes abnormalities of bone, joints, fingernails and kidneys mainly involving organs of both ectodermal and mesodermal origin.The diagnostic tetrad includes fingernail dysplasia, absent or hypoplastic patellae, the presence of posterior conical iliac horns, and deformation or luxation (ie, hypoplasia) of the radial heads. Kidney disease and glaucoma are now recognized as part of the syndrome. The most serious complication associated with nail-patella syndrome is nephropathy.

Causes 

• The Nail-Patella syndrome is inherited via autosomal dominancy that is linked to Mutations in the gene encoding transcription factor LMX1B, mapped on the long arm of chromosome 9 (9q34).
• The frequency of the occurrence is 1/50,000.
• The disorder is linked to the ABO blood group locus and the enzyme adenylate kinase.
• There is an indirect evidence that glaucoma-related genetic material is located at that same
• A genetic abnormality is believed to lead to altered connective tissue metabolism with widespread structural defects in collagen.
• Abnormal collagen deposition in the glomeruli probably causes the nephropathy associated with Nail-patella syndrome.
• There is no racial predominance and preferable age of onset, both sexes are equally effected.

 

Symptoms and Signs

Nails

• Patients have different degrees of nail dysplasia. The nails, especially those on the thumbs, are typically absent or short and never reach the free edge of the finger, is more severe on the ulnar side than on the radial side. The toenails are rarely affected.
• Other nail abnormalities  include splitting, longitudinal ridging, koilonychia, poor lunula formation, and discoloration.
• V-shaped triangular lunulae with a distal peak in the midline are pathognomonic for nail-patella syndrome.

    

Bones and joints

• Patellae are smaller or luxated, the knees may be unstable.
• The elbows may have limited motion (eg, limited pronation, supination, extension).
• Subluxation of the radial head may occur.
• Arthrodysplasia of the elbows.
• General hyperextension of the joints can be present.
• Exostoses arising from the posterior aspect of the iliac bones.
• Other reported bone changes include scoliosis, scapular hypoplasia, and the presence of cervical ribs.

    

Kidneys

• Renal disorders may result in only asymptomatic proteinuria, although hematuria, nephrotic syndrome, and progression to renal failure have been observed.
• Ankle edema and recurrent urinary tract infections can also be manifestations of renal involvement.
• Nephropathy is the only manifestation of nail-patella syndrome in some cases.

    

Eyes

• Hyperpigmentation of the pupillary margin of the iris.
• Other abnormalities, such as heterochromia of the iris with cloverleaf deformity, cataracts, microcornea, and glaucoma, have also been reported.

 

Other

• Skin laxity may be present.
• Webbing of the elbows and absent skin creases in the distal parts of the fingers are described in some patients.

Treatment

Medical Care

• No treatment is available for the cutaneous findings of nail-patella syndrome (NPS), also known as hereditary osteo-onychodysplasia (HOOD).
• Associated abnormalities require appropriate care from specialists-orthopedist, nephrologist, ophthalmologist and a genetic counsellor.    

Surgical Care

• Although more than 90% of patients with nail-patella syndrome have patellar involvement, most patients are asymptomatic and rarely require surgical treatment.
• However, congenital permanent dislocation of the patella (CPDP) should be treated with surgical procedures. Preferably, orthopedic correction should be performed when the patient is aged approximately 2-3 years to prevent secondary deformities and growth-related disability.