Okamoto syndrome (OS), also known as Au–Kline syndrome (AKS), is a very rare autosomal dominant genetic condition characterised by congenital hydronephrosis, low muscle tone, heart defects, intellectual disability and characteristic facial features. Those affected often have neurological and skeletal abnormalities, as well as frequent urinary tract infections. Language and walking are usually delayed. Facial features include prominent, downturned ears, an open, downturned mouth and drooping eyelids (ptosis).The syndrome is caused by mutations in the HNRNPK gene, which codes for heterogeneous nuclear ribonucleoprotein K. This protein is involved in the process of DNA transcription and translation into proteins. A mutation in this gene impairs DNA transcription, disrupting some developmental processes. As an autosomal dominant disorder, only one faulty copy of the gene is required for the condition to occur. The syndrome is typically diagnosed based on the physical symptoms and then confirmed by genetic testing.Treatment has centred around the symptoms. Sign language and assistive language technology can aid communication. The prognosis is not yet fully known, due to the lack of patients in literature, however most of the patients have at least lived through childhood. The urinary system defects have been the most significant contributors to mortality. As of May 2019, 26 individuals worldwide were known to be affected. The syndrome was first described in 1997 by Nobuhiko Okamoto et al., and the gene responsible was first identified in 2015 by Ping-Yee Billie Au, Antonie D. Kline et al. In 2019, Okamoto proposed that Au–Kline syndrome and Okamoto syndrome were synonymous.
Signs and symptoms
Kidneys
Individuals with Okamoto syndrome are usually born with hydronephrosis, or dilation of the internal structures of the kidneys, due to narrowing (stenosis) of the passage between the kidneys and the ureters (the ureteropelvic junction), leading to a build-up of urine. There is also often vesicoureteral reflux, in which urine passes backwards from the bladder to the ureters, and frequent urinary tract infections. Heart
Individuals with Okamoto syndrome are typically born with heart defects, which can include aortic valve stenosis, atrial or ventricular septal defect, bicuspid aortic valve or patent ductus arteriosus. Physical features
The syndrome has a characteristic facial appearance which is similar to that of Kabuki syndrome, including prominent, downward-displaced ears that are underdeveloped, long eyelids, epicanthic folds, a short, broad nose, an open, downturned mouth and a deep groove in the midline of the tongue. Cleft palate occurs in about half of those affected. There is sometimes webbing of the neck or bulging eyes, and less commonly there is excessive hair on the forehead or other parts of the body or a unibrow. Individuals with the syndrome may also have a broad first toe and crowding of the toes, and at least two affected individuals have had polydactyly of the fifth digit (postaxial polydactyly). Some of those affected have had undescended testicles (cryptorchidism). A small minority of those affected have had congenital joint contractures such as club foot. Neurological
Those with Okamoto syndrome typically have severe mental disability and are usually born with microcephaly.