Usually only males have the disorder. A few affected females with the clinical manifestations of Lowe syndrome have been reported [Cau et al 2006].
The major clinical manifestations found in males with Lowe syndrome involve the eyes, central nervous system, and kidneys. Nearly all post-pubertal heterozygous females have lens opacities; a few will have additional findings. With the wide availability of molecular genetic testing, phenotypic heterogeneity appears to be substantially greater than previously suspected, such that individuals who lack certain features of Lowe syndrome can still have pathogenic variants in OCRL.
Males
Eyes. Dense congenital cataracts, formed as a result of abnormal metabolism or migration of the embryonic lens epithelium, are found in all affected boys. Although present at birth, the cataracts may not be detected until a few weeks of life. Rarely, the lens opacities are so mild that they do not affect visual development, even into the teen years.
All boys have impaired vision; corrected acuity is rarely better than 20/100 [McSpadden 2000, Nussbaum & Suchy 2001]. With decreased visual acuity, nystagmus develops early in life, even with early and uncomplicated surgery. Self-stimulatory activity also increases, i.e., rhythmic flapping of the hands, eye rubbing, and repetitive rocking movements. Despite aggressive intervention, visual disability may progress to blindness.
Central nervous system. Generalized infantile hypotonia is noted soon after birth and is of central origin. Deep tendon reflexes are usually absent. Hypotonia may slowly improve with age, but neither normal motor tone nor strength is ever achieved.
Approximately 50% of affected boys have seizure disorders, most often of the generalized type and usually starting before age six years [McSpadden 2000].
Behavior problems (i.e., self-stimulation or stereotypic and obsessive-compulsive behaviors) are frequent and include many problems common to visually and intellectually handicapped individuals. Occasionally, violent tantrums or aggressive and self-abusive behaviors occur [Charnas & Gahl 1991, Kenworthy et al 1993].
Almost all affected males have some degree of intellectual impairment. Between 10% and 25% of affected males function in the low-normal or borderline range, approximately 25% function in the mild-to-moderate range, and 50%-65% function in the severe-to-profound range of intellectual disability [Kenworthy et al 1993]. Delayed language development is evident in early childhood. Most individuals learn to communicate verbally to some extent by age seven years; some eventually become quite verbal [McSpadden 2000]. Love of music and rhythm are notable.
As adults, most affected men reside with their families. A few are functional enough to live in a group home or even independently with appropriate assistance and guidance.
Kidneys. Affected boys have varying degrees of proximal renal tubular dysfunction of the renal Fanconi type. The features of symptomatic Fanconi syndrome do not usually become manifest until after the first few months of life, except for low molecular-weight (LMW) proteinuria.
The molecular size of albumin is at the upper end of the size range for LMW proteins, so the small percentage of albumin that is normally filtered by the glomerulus is also reabsorbed and metabolized by the proximal tubule via the LMW protein transport process.
In Lowe syndrome, proximal renal tubular dysfunction often leads to clinically apparent albuminuria (urine dipstick albumin 1-4+; nephrotic range proteinuria >1 g/m2/day in more than half), while serum albumin remains normal [Bökenkamp & Ludwig 2016]. Albuminuria is better known as a marker of glomerular injury in other diseases such as diabetes mellitus; in Lowe syndrome it likely reflects proximal tubular dysfunction, especially early in life before chronic renal failure occurs.
All boys have LMW proteinuria and albuminuria, likely due to downstream disordered endocytosis and postendocytic membrane trafficking in the proximal tubular cell [Cui et al 2010, De Matteis et al 2017]. Most boys have aminoaciduria [Bökenkamp & Ludwig 2016]. Some boys develop full-blown renal Fanconi syndrome with bicarbonaturia and renal tubular acidosis, phosphaturia with hypophosphatemia and renal rickets, sodium and potassium wasting, and polyuria with an apparent urine-concentrating defect from the massive solute loss in the urine. Few of these boys have renal glucose wasting, which is frequently observed in other diseases with full-spectrum renal Fanconi syndrome [Bockenhauer et al 2008, Bökenkamp & Ludwig 2016, Zaniew et al 2018]. Other boys have little or no bicarbonaturia and phosphaturia, but LMW proteinuria and hypercalciuria with nephrocalcinosis and nephrolithiasis (calcium oxalate and calcium phosphate stones) similar to Dent disease [Bockenhauer et al 2008, Bökenkamp & Ludwig 2016].
Progressive glomerulosclerosis likely results from progressive renal tubular injury, which eventually may lead to chronic kidney disease (CKD) and end-stage renal disease (ESRD) between the second and fourth decades of life [McSpadden 2000, Nussbaum & Suchy 2001, Zaniew et al 2018].
Life span. Most males do not live past age 40 years. In older individuals, death has been related to progressive renal failure or scoliosis. Death from dehydration, pneumonia, and infections occurs at all ages [McSpadden 2000].
Short stature. Although birth length is usually normal, linear growth velocity is below normal and short stature becomes evident by age one year. The average adult height is approximately 155 cm [McSpadden 2000]. CKD and acidosis along with renal rickets or other bone disease may contribute to the short stature. Some boys have been treated with growth hormone, resulting in an increase in height but persistence of short stature for age [Zaniew et al 2018].
Feeding and gastrointestinal concerns
Slow weight gain may occur because of insufficient caloric intake.
Gastroesophageal reflux, most common in infancy, may be seen at any age.
Aspiration of food along with a decreased ability to cough effectively to clear lung fields may lead to atelectasis, pneumonia, or chronic lung disease.
Poor abdominal muscle tone increases the risk for chronic constipation and the development of (predominantly inguinal) hernias.
Bone disease in affected boys may be related to Fanconi syndrome with phosphaturia, inadequate renal production of 1,25-dihydroxyvitamin D, and chronic acidosis as well as CKD. The bone disease may appear as classic changes of rickets on bone radiographs.
However, even in the presence of well-corrected Fanconi syndrome and no findings of rickets, some boys have repeat pathologic bone fractures with poor healing and bone demineralization on radiographs or bone densitometry [E Brewer, personal observation].
Whether some of the bone disease is related to inactivity resulting from muscle hypotonia and immobilization in severely affected boys or to a primary defect in bone mineralization/molecular transport requires further study.
Other musculoskeletal concerns
Genitourinary issues
Teeth and skin findings. Dental malformations and generalized mobility of primary teeth with decreased or dysplastic dentin formation may also be related to a primary dental abnormality in Lowe syndrome [Harrison et al 1999].
Superficial cysts may occur in the mouth and on the skin, especially the scalp, lower back and buttocks.The skin cysts may become painful and occasionally infected. Histologic examination revealed epidermal cysts in which the dermis was lined by several layers of stratified squamous epithelium with a granular layer and filled with keratin flakes [Ikehara & Utani 2017]. Cysts have also been found in imaging studies of the kidneys and brain. These findings suggest that an abnormality in connective tissue may also be involved in the pathogenesis of the disorder [McSpadden 2000, Kim et al 2014, Murakami et al 2018].
Coagulation disorder. The OCRL-1 protein is found in human platelets. Prolonged or delayed bleeding following surgery, such as cataract extraction has been reported. An intrinsic platelet defect in these individuals that can be detected using a platelet function analyzer (PFA-100) was identified; other coagulation profile related tests, including platelet counts, gave normal results [Lasne et al 2010]. In another study, thrombocytopenia/low normal platelets were found in about 20% [Recker et al 2015].
Females
Approximately 95% of postpubertal heterozygous females have characteristic findings in the lens of each eye on slit lamp examination through a dilated pupil by an experienced ophthalmologist. The lens findings have correlated with the results of molecular genetic studies in predicting heterozygosity for the pathogenic variant in OCRL in postpubertal females [Lin et al 1999, McSpadden 2000, Röschinger et al 2000, Nussbaum & Suchy 2001]. While the lens findings may appear in prepubertal females as well (especially the less common axial posterior central opacity), their absence does not exclude the possibility of heterozygosity.
Most heterozygous females show numerous irregular, punctate, smooth, off-white (white to gray) opacities, present in the lens cortex, more in the anterior cortex than the posterior cortex, and distributed in radial bands that wrap around the lens equator. Classically, the nucleus is spared. On retroillumination, the opacities are distributed in a radial, spoke-like pattern and can be relatively dense in a wedge shape comparable to an hour or two on the face of a clock, alternating with a similar-sized wedge with few to no opacities.
A few heterozygous females (~10%) have a dense central precapsular dead-white cataract at the posterior pole of the lens that may be visually significant if it is large. Similarly, the cataracts in some heterozygous females may become visually significant by the fourth decade and require surgery without the diagnostic importance being recognized.
The manifestations of Lowe syndrome besides those seen in the lens are not observed in heterozygous females unless there is either rare X;autosome translocation with the X chromosome breakpoint at OCRL or extremely skewed X inactivation. In an example of the latter, a female with two structurally normal X chromosomes showed classic, severe Lowe syndrome as a result of a familial defect in X inactivation inherited from her father. The paternally derived X chromosome containing a normal OCRL gene remained inactive in 100% of cells, while the maternally derived X chromosome carrying a pathogenic variant of ORCL was active in 100% of cells tested [Cau et al 2006].