Welcome to the HHRH Community: A Starting Guide

Receiving a diagnosis of Hereditary Hypophosphatemic Rickets with Hypercalciuria (HHRH) often marks the end of a long “diagnostic odyssey” for many families. Because this condition is an ultra-rare disease—with an estimated prevalence of roughly 1 in 250,000 people—most local doctors and even many specialists may have never seen a case before ^[1][2]. You may find yourself becoming the resident expert on the condition, navigating a complex path that involves both bone health and kidney function. While primarily diagnosed in childhood, some individuals are not correctly diagnosed until adulthood when they experience recurrent fractures or kidney stones.

Understanding HHRH

HHRH is a genetic disorder that affects how the body manages phosphate and calcium. It is caused by changes (mutations) in the SLC34A3 gene, which provides instructions for a “transporter” protein in the kidneys ^[3]. This transporter is responsible for reclaiming phosphate from the urine and putting it back into the bloodstream.

In HHRH, this transporter does not work correctly, leading to two primary issues:

1. Phosphate Wasting: The kidneys lose too much phosphate in the urine (phosphaturia). Without enough phosphate in the blood (hypophosphatemia), bones cannot harden properly, leading to rickets (softening and weakening of bones in children) or osteomalacia (bone softening in adults) ^[1][4].
2. Calcium Excretion: Due to the way the body tries to compensate for low phosphate, it produces high levels of its own active vitamin D (1,25-dihydroxyvitamin D). This causes the gut to absorb extra calcium, and the kidneys to release more calcium into the urine (hypercalciuria) ^[1][3].

A Dual-System Challenge

HHRH is unique because it is a “dual-system” disease. While many forms of rickets only require focusing on the bones, HHRH families must carefully balance the health of the skeleton with the health of the kidneys.

• Bone Health: Symptoms often include leg bowing, bone pain, slow growth, and an increased risk of fractures ^[5][6].
• Kidney Health: High levels of calcium in the urine put patients at increased risk for nephrolithiasis (kidney stones) and nephrocalcinosis (calcium deposits in the kidney tissue). In some study cohorts, approximately half of individuals with HHRH developed one of these kidney complications over time, though individual risk varies ^[1][4].

Managing HHRH requires a delicate dance: providing enough phosphate to heal the bones without worsening the calcium levels in the urine, which could stress the kidneys.

Navigating the Emotional Impact

Caring for a child—or living as an adult—with an ultra-rare disease brings significant practical and emotional weight. It is normal to feel:

• Isolation: Because the disease is so rare, finding other families who truly understand your daily reality can be difficult ^[7].
• Genetic Guilt: Since HHRH is an autosomal recessive condition (meaning a child usually inherits one mutated gene from each parent), parents sometimes experience guilt. It is vital to remember that this is nobody’s fault; we cannot control the genes we pass down ^[8][9]. A genetic counselor can help explain recurrence risks for future pregnancies.
• Healthcare Fatigue: Coordinating between multiple specialists—such as endocrinologists (hormone and bone specialists) and nephrologists (kidney specialists)—can feel like a full-time job ^[10][11].

What to Expect After Diagnosis

Once HHRH is confirmed through genetic testing, care will shift toward stabilizing chemistry and protecting growth.

• Specialized Care: You will likely work with a multidisciplinary team. It is common to have regular appointments for blood work and urine tests to monitor phosphate, calcium, and vitamin D levels ^[5][12].
• Imaging: Periodic renal ultrasounds are utilized to check for kidney stones or calcium deposits ^[5][13].
• Treatment Differences: It is crucial to know that HHRH is treated differently than more common types of rickets. For example, in HHRH, active vitamin D analogs (like calcitriol) are avoided because they can dangerously increase calcium in the urine ^[1][14].
• Family Screening: Because HHRH is genetic, doctors may recommend testing siblings or checking parents, as carriers of a single mutation can sometimes still be prone to kidney stones ^[15][16].

Everyday Lifestyle Note
Do not attempt to restrict dietary calcium to prevent kidney stones unless specifically instructed by your nephrologist; doing so can actually harm the bones further. Aim for a normal, age-appropriate calcium intake. Maintaining excellent daily hydration (drinking plenty of water) is one of the most effective ways to reduce the risk of kidney stones. Never alter phosphate doses on your own.

You are your own (or your child’s) most important advocate. A clear understanding of this bone-kidney connection is the first step in protecting long-term health.