Isolated unilateral tuberous sclerosis-associated renal cystic disease in a neonate

Diagnosis of tuberous sclerosis complex in the fetus

Tuberous sclerosis complex is a dominantly inherited genetic disorder of striking clinical variability. It is caused by mutations in either TSC1 or TSC2 gene, which regulate cell growth and proliferation by inhibition of mTORC1 signaling. TS is characterized by the development of benign tumors in many tissues and organs and its neurological manifestations include epilepsy, autism, cognitive and behavioral dysfunction, and giant cell tumors. With mechanism-based mTOR inhibitors therapy now available for many of its manifestations, early diagnosis of TSC is very important in order to offer appropriate care, long-term surveillance and parental counseling. Fetal ultrasound and MRI imaging techniques have evolved and may capture even earlier the following TSC-associated lesions: cardiac rhabdomyomas, subependymal nodules, cortical tubers and renal cysts. Often these represent an incidental finding during a routine ultrasound. Furthermore, in the past decades prenatal molecular diagnosis of TSC has emerged as an important option for families with a known affected member; however, the existing evidence with regards to the clinical characteristics and long-term outcome of babies diagnosed prenatally with TSC is yet limited and the path that follows early TSC detection merits further research.

The concept of type 2 segmental mosaicism, expanding from dermatology to general medicine

In autosomal dominant skin disorders, the well-known type 1 segmental mosaicism reflects heterozygosity for a postzygotic new mutation. By contrast, type 2 segmental mosaicism originates in a heterozygous embryo from an early postzygotic mutational event giving rise to loss of the corresponding wild-type allele, which results in a pronounced segmental involvement being superimposed on the ordinary, non-segmental phenotype. Today, this concept has been proven by molecular analysis in many cutaneous traits. The purpose of this review was to seek publications of cases suggesting an extracutaneous manifestation of type 2 segmental mosaicism. Case reports documenting a pronounced extracutaneous segmental involvement were collected from the literature available in PubMed and from personal communications to the author. Pertinent cases are compared to the description of cutaneous segmental mosaicism of type 1 or type 2 as reported in a given trait. In total, reports suggesting extracutaneous type 2 segmental mosaicism were found in 14 different autosomal dominant skin disorders. In this way, clinical evidence is accumulated that extracutaneous type 2 segmental mosaicism does likewise occur in many autosomal dominant skin disorders. So far, however, molecular proof of this particular form of mosaicism is lacking. The present review may stimulate readers to inform colleagues of other specialties on this new concept, in order to initiate further research in this particular field of knowledge that has important implications for diagnosis, treatment and genetic counselling.

Fetal and Postnatal Magnetic Resonance Imaging of Unilateral Cystic Renal Dysplasia in a Neonate with Tuberous Sclerosis

Tuberous sclerosis (TS) is an autosomal dominant condition associated with mutations in the TSC1 and/or TSC2 genes. Clinical manifestations are multisystemic, and they often include lesions in the brain, skin, heart, kidneys, and bones. TSC2 gene mutations can be seen concomitantly with autosomal dominant polycystic kidney disease gene mutations. We present a case of a fetus with prenatal diagnosis of TS that had unique asymmetrical distribution of renal cystic disease. We describe the extensive work up with both fetal and neonatal magnetic resonance imaging with correlating images of the unilateral polycystic renal disease in addition to typical TS brain findings.

Imaging features of tuberous sclerosis complex with autosomal-dominant polycystic kidney disease: a contiguous gene syndrome

BACKGROUND

Genes for tuberous sclerosis complex (TSC) type 2 and autosomal-dominant polycystic kidney disease (ADPKD) type 1 are both encoded over a short segment of chromosome 16. When deletions involve both genes, an entity known as the TSC2/ADPKD1 contiguous gene syndrome, variable phenotypes of TSC and ADPKD are exhibited. This syndrome has not been reviewed in the radiology literature. Unlike renal cysts in TSC, cystic disease in TSC2/ADPKD1 contiguous gene syndrome results in hypertension and renal failure. A radiologist might demonstrate polycystic kidney disease before the patient develops other stigmata of TSC. Conversely, in patients with known TSC, enlarged and polycystic kidneys should signal the possibility of the TSC2/ADPKD1 contiguous gene syndrome and not simply TSC. Distinguishing these diagnoses has implications in prognosis, treatment and genetic counseling.

OBJECTIVE

To describe the clinical and imaging findings of tuberous sclerosis complex and polycystic kidney disease in seven pediatric patients.

MATERIALS AND METHODS

We retrospectively reviewed renal and brain imaging of children and young adults with genetically proven or high clinical suspicion for TSC2/ADPKD1 contiguous gene syndrome.

RESULTS

We included seven pediatric patients from two referral institutions. Ages ranged from birth to 21 years over the course of imaging. The mean follow-up period was 9 years 8 months (4 years 6 months to 20 years 6 months). No child progressed to end-stage renal disease during this period. Three patients were initially imaged for stigmata of TSC, three for abdominal distension and one for elevated serum creatinine concentration. All patients developed enlarged, polycystic kidneys. The latest available imaging studies demonstrated that in 12 of the 14 kidneys 50% or more of the parenchyma was ultimately replaced by >15 cysts, resulting in significant cortical thinning. The largest cysts in each kidney ranged from 2.4 cm to 9.3 cm. Echogenic lesions were present in 13 of the 14 kidneys, in keeping with angiomyolipomas (ranging from 0.4 cm to 7.8 cm). Compared to the latest imaging studies, the initial studies only demonstrated 64% of kidneys to be borderline or enlarged; the majority had 10 or more cysts and 0-5 echogenic foci in each kidney, measuring 0.8 cm maximally, which were possible angiomyolipomas. Increased cortical echogenicity was observed in eight kidneys, and decreased corticomedullary differentiation was demonstrated in six kidneys. Cortical thinning varied with size and number of cysts.

CONCLUSION

The sonographic renal findings in TSC2/ADPKD1 contiguous gene syndrome progress over time and demonstrate a specific pattern of renal disease different from typical tuberous sclerosis complex. There are multiple cysts at presentation and there is progressive enlargement of the kidneys and of the renal cysts. Because clinical or imaging findings of TSC may not manifest in the young child, the radiologist can be the first to suggest a diagnosis of TSC2/ADPKD1 contiguous gene syndrome and recommend thorough skin examination and imaging in search of TSC findings. The radiologist should be able to suggest the diagnosis of TSC2/ADPKD1 contiguous gene syndrome in children with TSC who have large cysts occupying a large portion of an enlarged kidney. This should not be dismissed as renal cystic disease of TSC or as ADPKD because the diagnosis of TSC2/ADPKD1 contiguous gene syndrome has implications for patient management and prognosis.