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PubMed This is a summary of 17 peer-reviewed journal articles Updated
Pediatrics

Recognizing the Symptoms and Warning Signs of LPI

At a Glance

Lysinuric protein intolerance (LPI) symptoms typically begin when a baby transitions to solid, high-protein foods. The classic warning signs include failure to thrive, a strong aversion to eating protein, and an enlarged liver and spleen. Eating protein can trigger a dangerous buildup of ammonia.

Recognizing the symptoms of Lysinuric protein intolerance (LPI) can be challenging because they often mimic common childhood illnesses. However, the timing and combination of these symptoms create a specific pattern. For many families, the “Aha!” moment comes when they realize their child’s health changed precisely when their diet changed.

The Timeline: Why Weaning is a Turning Point

In most cases, infants with LPI appear healthy at birth and grow normally while they are exclusively breastfed or on standard infant formula [1]. This is because the protein content in these early foods is relatively low.

The symptoms typically begin during weaning—the transition to solid foods—or when high-protein foods like cow’s milk, eggs, or meat are introduced [2]. At this stage, the body’s inability to transport specific amino acids (lysine, arginine, and ornithine) causes the urea cycle to struggle [3][4]. This results in a buildup of ammonia, a toxic waste product, leading to the first noticeable signs of the condition [5].

Common Early Symptoms

If you are wondering if LPI explains your child’s experience, look for this “triad” of classic findings:

  • Failure to Thrive and Growth Retardation: This is often the most visible sign. Despite having an appetite, children may struggle to gain weight or grow in height at the expected rate [6][7]. This occurs because the body is not getting the “building blocks” (amino acids) it needs to grow [2].
  • Protein Aversion: This is a unique behavioral symptom. Children with LPI often develop a deep, natural dislike for protein-rich foods [1]. They may “act out,” refuse to eat meat or dairy, or seem much happier eating only starches, fruits, and vegetables [2]. This is the body’s way of protecting itself from the sickness caused by protein ingestion.
  • Organ Enlargement (Hepatosplenomegaly): Doctors may find that the liver (hepatomegaly) and the spleen (splenomegaly) are enlarged during a physical exam [2][8].

Other common symptoms include chronic diarrhea, severe gastrointestinal distress, and anemia (low red blood cell count) [6][9].

Red Flags: Understanding Hyperammonemia

The most dangerous aspect of LPI is hyperammonemia, or high levels of ammonia in the blood [10]. When a child with LPI eats more protein than their body can handle, ammonia levels can spike. This is a medical emergency that requires immediate attention [11].

Behavioral and Physical Signs of an Ammonia Spike:

  • Vomiting and Nausea: Often occurring shortly after a meal containing protein [12].
  • Altered Behavior: Irritability, extreme fussiness, “brain fog”, unusual inconsolability, a “glassy-eyed” stare, or a sudden loss of recent developmental milestones [12].
  • Lethargy and Confusion: The child may seem unusually sleepy, difficult to wake up, or disoriented [13].
  • Loss of Consciousness or Seizures: These are severe signs of a metabolic crisis and require an immediate call to emergency services [14].

The Road to Diagnosis: Common Misdiagnoses

Because LPI is so rare, it is frequently confused with other conditions before the correct diagnosis is made [15]. It is common for children to first be tested for:

  1. Celiac Disease: Due to the failure to thrive and chronic diarrhea [6].
  2. Milk Protein Allergy: Because symptoms often start when cow’s milk is introduced [6].
  3. General Malnutrition: If laboratory tests are done while a child is severely malnourished, the typical LPI “markers” in the blood and urine might actually look normal, masking the disease [6].
  4. Urea Cycle Disorders: LPI shares many symptoms with other disorders that cause high ammonia, but the specific pattern of amino acids in the urine helps specialists tell them apart [6][16].

If your child has been treated for these conditions but isn’t getting better, a metabolic evaluation for LPI may be an important next step [17].

Common questions in this guide

Why do LPI symptoms usually start when a baby transitions to solid foods?
Infants with LPI often grow normally while breastfeeding or drinking standard formula because the protein content is low. Symptoms usually begin when they are weaned onto high-protein foods like cow's milk, eggs, or meat, which their bodies cannot properly process.
What is protein aversion in children with LPI?
Protein aversion is a behavioral symptom where children naturally dislike and refuse protein-rich foods like meat or dairy, preferring fruits, vegetables, and starches instead. This is the body's way of protecting itself from the sickness caused by a toxic buildup of ammonia when digesting protein.
How do I recognize an ammonia spike in my child?
A dangerous spike in ammonia, known as hyperammonemia, can cause vomiting, extreme fussiness, lethargy, or confusion shortly after eating protein. In severe cases, it can lead to a loss of consciousness or seizures, which requires immediate emergency medical attention.
Can LPI be misdiagnosed as other childhood illnesses?
Yes, because it is so rare, LPI is frequently misdiagnosed as celiac disease, a milk protein allergy, or general malnutrition. The combination of chronic diarrhea and failure to thrive often leads doctors to suspect these more common conditions first before conducting a metabolic evaluation.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.My child seems to refuse meat and eggs—is this a typical 'protein aversion' seen in LPI?
  2. 2.Could my child's history of being diagnosed with 'celiac disease' or 'malnutrition' actually have been undiagnosed LPI?
  3. 3.What specific signs of confusion or behavioral changes should I look for that indicate an ammonia spike?
  4. 4.If my child starts vomiting and becomes lethargic, what is the exact step-by-step emergency protocol we should follow?
  5. 5.Is the enlargement of my child's liver and spleen directly related to how their body is processing amino acids?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (17)
  1. 1

    [Enteral nutrition support for lysinuric protein intolerance: a case report and literature review].

    Quan J, Liu XF, Hu K, Hou Q

    Zhongguo dang dai er ke za zhi = Chinese journal of contemporary pediatrics 2023; (25(12)):1270-1275 doi:10.7499/j.issn.1008-8830.2306148.

    PMID: 38112146
  2. 2

    [Clinical features of children with lysinuric protein intolerance and SLC7A7 gene mutation: an analysis of 3 cases].

    Cui D, Hu YH, Tang G, et al.

    Zhongguo dang dai er ke za zhi = Chinese journal of contemporary pediatrics 2019; (21(4)):375-380.

    PMID: 31014432
  3. 3

    Dual pathogenic mechanisms in lysinuric protein intolerance: Interplay between hyperammonemia and cellular metabolic dysregulation in astrocyte injury.

    Kakisaka K, Sato T, Wada Y, et al.

    Molecular genetics and metabolism 2025; (145(2)):109134 doi:10.1016/j.ymgme.2025.109134.

    PMID: 40349487
  4. 4

    y+LAT1 and y+LAT2 contribution to arginine uptake in different human cell models: Implications in the pathophysiology of Lysinuric Protein Intolerance.

    Rotoli BM, Barilli A, Visigalli R, et al.

    Journal of cellular and molecular medicine 2020; (24(1)):921-929 doi:10.1111/jcmm.14801.

    PMID: 31705628
  5. 5

    Hyperammonemia in a Child Presenting with Growth Delay, Short Stature, and Diarrhea.

    Almontashiri NAM, Demirbas D, Berry GT, Peake RWA

    Clinical chemistry 2018; (64(8)):1260-1262 doi:10.1373/clinchem.2018.291146.

    PMID: 30054302
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    Lysinuric protein intolerance: Pearls to detect this otherwise easily missed diagnosis.

    Alqarajeh F, Omorodion J, Bosfield K, et al.

    Translational science of rare diseases 2020; (5(1-2)):81-86 doi:10.3233/TRD-190035.

    PMID: 33134088
  7. 7

    Delayed skeletal development and IGF-1 deficiency in a mouse model of lysinuric protein intolerance.

    Stroup BM, Li X, Ho S, et al.

    Disease models & mechanisms 2023; (16(8)) doi:10.1242/dmm.050118.

    PMID: 37486182
  8. 8

    Lysinuric protein intolerance presenting as pancytopenia and splenomegaly mimicking acute leukaemia: a case report.

    Lokuhewage C, Pathiraja H, Madawala P, et al.

    BMC pediatrics 2023; (23(1)):382 doi:10.1186/s12887-023-04207-7.

    PMID: 37528333
  9. 9

    Imbalance of plasma amino acids, metabolites and lipids in patients with lysinuric protein intolerance (LPI).

    Kurko J, Tringham M, Tanner L, et al.

    Metabolism: clinical and experimental 2016; (65(9)):1361-75.

    PMID: 27506743
  10. 10

    Lysinuric protein intolerance: Unusual clinical manifestations in a compound heterozygote with a novel pathogenic variant.

    Pascual López JR, Wu W, Konczal L

    Biochemistry and biophysics reports 2025; (44()):102229 doi:10.1016/j.bbrep.2025.102229.

    PMID: 41189639
  11. 11

    Acute Presentation and Management of the Encephalopathic Child With an Undiagnosed Inborn Error of Metabolism.

    Bennett EE, Hummel K, Smith AG, Longo N

    The Journal of emergency medicine 2019; (56(1)):e5-e8 doi:10.1016/j.jemermed.2018.09.037.

    PMID: 30420308
  12. 12

    Lysinuric Protein Intolerance Presenting with Recurrent Hyperammonemic Encephalopathy.

    Bijarnia-Mahay S, Jain V, Bansal RK, et al.

    Indian pediatrics 2016; (53(8)):732-4 doi:10.1007/s13312-016-0920-2.

    PMID: 27567650
  13. 13

    The utility of EEG monitoring in neonates with hyperammonemia due to inborn errors of metabolism.

    Wiwattanadittakul N, Prust M, Gaillard WD, et al.

    Molecular genetics and metabolism 2018; (125(3)):235-240 doi:10.1016/j.ymgme.2018.08.011.

    PMID: 30197275
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    Pearls & Oy-sters: Chemotherapy-associated hyperammonemic encephalopathy.

    Neves Briard J, Lezaic N, Keezer MR

    Neurology 2020; (94(8)):e874-e877 doi:10.1212/WNL.0000000000009004.

    PMID: 31992681
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    Lysinuric protein intolerance caused by a homozygous SLC7A7 deletion and presented with hyperferritinemia and osteoporosis in two siblings.

    Kalay I, Aykut H, Caliskan Z, et al.

    Molecular genetics and metabolism reports 2023; (37()):101022 doi:10.1016/j.ymgmr.2023.101022.

    PMID: 38053936
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    Improving a Rare Metabolic Disorder Through Kidney Transplantation: A Case Report of a Patient With Lysinuric Protein Intolerance.

    IJzermans T, van der Meijden W, Hoeks M, et al.

    American journal of kidney diseases : the official journal of the National Kidney Foundation 2023; (81(4)):493-496 doi:10.1053/j.ajkd.2022.08.019.

    PMID: 36223829
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    The utility of reverse phenotyping: a case of lysinuric protein intolerance presented with childhood osteoporosis.

    Avci Durmusalioglu E, Isik E, Ayyildiz Emecen D, et al.

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    PMID: 33823103

This page provides educational information on the symptoms and warning signs of Lysinuric protein intolerance (LPI). It is not a substitute for professional medical evaluation. If you suspect your child is experiencing a metabolic crisis or ammonia spike, seek emergency medical care immediately.

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